IGT PhD Projects 2017

Contents

Dynamics of mantle convection with realistic material properties ........................................ 1

Observing volcanic eruption dynamics from satellite radar intensity data ............................. 5

Active Tectonics & Fault Geomorphology around Major Cities of the Northern Tien Shan .... 9

Magmatic volatile contents and storage time-scales for rift-related volcanism in Ethiopia .. 13

Constructing geochemical analogues of the asthenosphere: Earth's largest geochemical

reservoir ............................................................................................................................. 17

Observing and modelling transient slip events on creeping faults ....................................... 21

Probing magma plumbing systems beneath volcanic calderas in the Galapagos Islands ...... 25

Tracking and measuring volcanic plumes using drones ........................................................ 28

Building a realistic model of Earth's magnetic field using constrained dynamics.................. 32

The evolution of porphyry-epithermal gold systems using trace element mobility and

concentration...................................................................................................................... 35

Fixing the fossil record! Experimentally decrypting the altered isotope archive preserved in

ancient carbonates.............................................................................................................. 38

Seismic detection of hidden primordial regions in the Earth's lowermost mantle................ 43

Magmatic mass transfer through deep crust ....................................................................... 47

Towards an understanding of Earth's structure - The development of adaptive optics

approaches for Seismology ................................................................................................. 52

Petrological & geochemical insights into subduction initiation- the case of Izu-Bonin-Mariana

volcanic arc ......................................................................................................................... 57

Anisotropy and anelasticity of HCP metals: a key to the dynamics of Earth's inner core ...... 61

The relationship between short-term tectonics and mountain building in New Zealand ..... 65

1

Dynamics of mantle convection with realistic material properties

Supervisors: Dr Chris Davies and Dr Andrew Walker

School of Earth and Environment, University of Leeds

Contact email: c.davies@leeds.ac.uk

Convection in rocky or icy planetary mantles controls the long-term evolution of the terrestrial

planets and many of the moons in the solar system. The style of mantle convection is intimately

linked to planetary habitability: it determines whether surface material participates in the global-

scale dynamics (as on Earth) or remains isolated (as on Venus) and also determines the viability of

magnetic field generation in the liquid core. The rich and complex dynamics exhibited by the

terrestrial planets arise since the physical properties that characterise mantle material are

enormously sensitive to small changes in temperature, pressure and composition. The nonlinear

feedbacks between transport properties (e.g. thermal conductivity and viscosity) and flow dynamics

are most prevalent in the upper and lower regions of the mantle, the so-called boundary layers, and

it is the behaviour in these regions that is largely responsible for the diversity of planetary behaviour

and evolution. The overall aim of this project is to quantitatively analyse the boundary layer

dynamics of mantle convection using computer simulations that couple fluid dynamics with state-of-

the-art transport properties obtained from mineral physics.

Boundary layers are thin regions at the top and bottom of a convecting system where temperature,

composition and flow change dramatically in order to meet externally-imposed conditions (Figure 1).

These regions are thought to control the efficiency of heat transfer into and out of the mantle and

therefore dictate the long-term thermal evolution of terrestrial planets [1]–[3]. There have been

extensive efforts to build physical models of heat transfer in mantle boundary layers using results

from numerical simulations of varying complexity [4]–[6], but the results are extremely varied and

lead to dramatically different predictions when applied to planets. The discrepancy centres on the

treatment of material properties, specifically thermal conductivity and viscosity. Most studies that

focus on boundary layer dynamics assume that these properties vary with depth and/or with

temperature [6]–[9]. However, the reality is that mantle properties will depend strongly on chemical

composition as well as the stable mineral phase at a given location (Figure 2). These dependencies

are now being revealed by mineral physics calculations constrained by seismic observations of deep

Earth structure. The time is ripe to use this information in fluid dynamical models to elucidate the

role of realistic material properties in determining the dynamics and evolution of mantle convection.

2

Figure 1. Time evolution of temperature (top) and composition (bottom) in an example mantle convection

model [10]. Note the remarkable spatial and temporal variations that occur near the lower boundary.

Figure 2. Cartoon illustrating the complex nature of the lowermost mantle [11]. Two large low shear velocity

provinces (LLSVP’s) encompass ~30% of the core-mantle boundary (CMB) at the present-day. These regions are

thought to be hotter (shown by background colour), chemically distinct from surrounding mantle material and

contain small-scale heterogeneity of their own, including the ultra-low velocity zones (ULVZ’s).

The project

You will undertake numerical simulations of mantle convection with spatially-varying thermal

conductivity and viscosity. You will use these models to quantify heat transfer and flow dynamics

with a view to developing simplified models of the fundamental physics. The first stage is to begin

with 2D models and simple parameterizations of the material properties since this is the

configuration used by most previous studies. Using the 2D model you will systematically add more

3

complex dependencies between material and thermodynamic properties, approaching the

predictions made by mineral physics calculations. This understanding will permit a numerical study

of the 3D case where statistical measures of boundary layer behaviour can be compared with

observations of the Earth, and boundary layer heat-flux can be used to explore the long-term

evolution of the terrestrial planets.

Training environment

You will receive training in skills tailored to the project but also useful to help secure a future career

as a research scientist in academia or elsewhere. To allow you to complete the project you will learn

the principles and practice of computational fluid dynamics with focus on the specifics pertaining to

mantle convection. You will need to understand the physics of convection and become skilled in

some of the mathematical and computational techniques needed to analyse the simulation results.

These advanced methods have obvious utility in a wide range of academic and industrial settings

such as the automotive and aerospace industries, climate and ocean simulation, and finance. You

will also learn how to confidently develop software for the analysis of results and to use large-scale

high performance computing resources such as those available at the University of Leeds and the

ARCHER national capability computing facility. Alongside the transferable skills in communication

and management this can open a wide range of career pathways. These skills will be developed by a

mixture of hands on experience, attending external training courses, and by participating in the

Leeds – York NERC doctoral training partnership programme

Student profile

You will have a good first degree in the physical or mathematical sciences (e.g. physics, geophysics,

chemistry, mathematics or computer science) that included modules on fluid dynamics or Earth

dynamics. The ideal candidate will also have experience of basic scientific programming and

computation possibly derived from the completion of an undergraduate research project.

References and further reading

1. J. Korenaga, “Urey ratio and the structure and evolution of Earth’s mantle,” Rev. Geophys.,

vol. 46, p. 2007RG000241, 2008.

2. C. Jaupart, S. Labrosse, and J. C. Mareschal, “Temperatures, Heat and Energy in the Mantle

of the Earth,” Treatise Geophys., vol. 7, no. February, pp. 253–303, 2007.

3. P. Driscoll and D. Bercovici, “On the thermal and magnetic histories of Earth and Venus:

Influences of melting, radioactivity, and conductivity,” Phys. Earth Planet. Int., vol. 236, pp.

36–51, 2014.

4. C. Grigne and S. Labrosse, “Convective heat transfer as a function of wavelength :

Implications for the cooling of the Earth,” J. Geophys. Res., vol. 110, pp. 1–16, 2005.

5. G. F. Davies, “Mantle regulation of core cooling: A geodynamo without core radioactivity?,”

Phys. Earth Planet. Int., vol. 160, pp. 215–229, 2007.

6. J. Korenaga, “Scaling of stagnant-lid convection with Arrhenius rheology and the effects of

mantle melting,” Geophys. J. Int., pp. 154–170, 2009.

7. L. Moresi and V. Solomatov, “Mantle convection with a brittle lithosphere : thoughts on the

global tectonic styles of the Earth and Venus,” J. Geophys. Res., pp. 669–682, 1998.

4

8. S. A. Hunt, D. R. Davies, A. M. Walker, R. J. Mccormack, A. S. Wills, D. P. Dobson, and L. Li,

“On the increase in thermal diffusivity caused by the perovskite to post-perovskite phase

transition and its implications for mantle dynamics,” vol. 320, pp. 96–103, 2012.

9. N. Tosi, D. A. Yuen, N. De Koker, and R. M. Wentzcovitch, “Mantle dynamics with pressure-

and temperature-dependent thermal expansivity and conductivity,” Phys. Earth Planet.

Inter., vol. 217, pp. 48–58, 2013.

T. Nakagawa and P. J. Tackley, “Implications of high core thermal conductivity on {E}arth’s

coupled mantle and core evolution,” Geophys. Res. Lett., vol. 40, pp. 1–5, 2013.

E. J. Garnero, A. K. McNamara, and S.-H. Shim, “Continent-sized anomalous zones with low

seismic velocity at the base of Earth’s mantle,” Nat. Geosci., vol. 9, no. June, p. 481, 2016.

5

Observing volcanic eruption dynamics from satellite radar intensity data

Supervisors: Dr Susanna Ebmeier1, Dr Mike Poland2, Professor Tim Wright1 1School of Earth and Environment, University of Leeds 2 United States Geological Survey (USGS)

Project partner: CEOS Volcano Pilot project

Contact email: s.k.ebmeier@leeds.ac.uk

Volcanic eruptions cause major changes to the topography and surface properties of the Earth that

can be detected from space. This project will lead to advances in our ability to monitor the dynamics

of ongoing eruptions using satellite data, by measuring changes in backscattered microwave

radiation intensity caused by the emplacement of eruptive products. The volume, physical

properties and temporal variability in the deposition of lavas, pyroclastic flows and ash are linked to

conditions within the volcano and subsurface. For example, tracking individual lava flows provide

insight into changes in magma supply rate through a conduit (e.g. Wadge et al., 2012) and

observations of changes at the surface of a lava dome caused by high extrusion rates provides

information about the ascent of magma (e.g., Goitom et al., 2015). Variations in backscattered

radiation intensity can therefore provide information about the state of an erupting volcano,

important for hazard assessment and forecasts.

The student will begin this project by examining the archive of high-resolution satellite radar imagery

acquired over Kīlauea volcano, Hawai’i, as part of the Group on Earth Observations supersite

programme (http://supersites.earthobservations.org/hawaii.php). This dataset spans both Kīlauea

summit and Puʻu ʻŌʻō vents during extended periods of lava effusion and major transitions in the

character of activity that resulted in significant changes to the Earth’s surface. The high density and

quality of in situ and remote geophysical measurements at Kīlauea mean that long term magma

supply rate and recent shallow magma dynamics have been well characterised (e.g., Anderson &

Poland, 2016; Poland & Carbone, 2016). Kīlauea is therefore an ideal location to examine the

potential of intensity data for linking surface intensity changes to the underlying subsurface

processes.

Synthetic Aperture Radar (SAR) images capture the intensity of radiation backscattered from the

Earth’s surface. After corrections to allow images with different geometries to be compared (e.g.,

radiometric terrain normalisation, Small, 2011), time series of the intensity of backscattered

radiation may be constructed. These can be used to map ashfall, the emplacement of flows, and

changes to lava domes during an eruption – particularly important for remote volcanoes with limited

ground-based infrastructure. Simple ratio-based change detection (e.g., Ebmeier et al., 2014) can be

improved upon by methods such as multiscale decomposition (Bovolo & Bruzzone, 2005) or

automatic thresholding using Bayesian inference (e.g., Meyer et al., 2015) to reliably identify fresh

eruption deposits. Information about the character of individual flow deposits (or about dome

growth) can then be understood in terms of changes to surface roughness, and volumes estimated

from radar shadow (e.g., Wadge et al., 2012; Arnold et al., 2016). Observations of transient stages of

flow-field and dome growth are particularly valuable, as these are otherwise only obtainable at a

few volcanoes worldwide where ground-based monitoring infrastructure is particularly extensive.

6

SAR has significant advantages for monitoring applications, especially as observations do not rely on

cloud free conditions or solar radiation. However, such data have not yet been widely integrated

into monitoring streams, in part due to high data costs. The usefulness of commercial radar intensity

imagery for monitoring was shown during the 2010 eruption of Merapi, when rates of lava dome

growth were estimated in near real time and used to forecast the development of the eruption

(Pallister et al., 2013). The student will use the insights from the examination of archive imagery over

Hawai’i to investigate the potential of the near-global, freely available Sentinel-1 SAR data for

monitoring eruptions.

Figure 1: Image of Kīlauea

volcano, Hawai’i, USA from

GoogleEarth. Both lava

effusion on the Eastern Rift

Zone from Puʻu ʻŌʻō vents

and activity at the relatively

young Halema’uma’u crater

at the summit have

produced topographic and

surface property changes.

Objectives

The student will work with scientists in Leeds and at the United States Geological Survey (USGS) to

investigate surface changes during volcanic unrest and eruption.

The student will start by using archive SAR imagery over Kīlauea, Hawai’i to examine the potential of

SAR intensity data for characterising eruption dynamics. This will involve developing novel tools

using approaches such as change detection, time series of radar intensity or phase correlation and

the integration of radar and optical satellite data.

As the student’s own research interests develop, further objectives could include multiple of:

• Using insights from research in Hawai’i to investigate lava flow dynamics using radar

backscatter intensity at other, less thoroughly monitored volcanoes. Additional test cases

will be selected in collaboration with the Centre for Earth Observations Satellite’s Volcano

Pilot Project in Latin America, to allow comparison of various radar instruments and

contribute to building remote sensing monitoring capacity in volcano observatories.

• Creating a module for the LICSAR processing software being developed at the University of

Leeds capable of producing radiometrically calibrated intensity images useful for volcano

monitoring. This would have the impact of making intensity data more accessible and useful

for volcano observatories all around the world.

• Mapping land use change and variations in vegetation in response to volcanic activity during

long-lived historical and ongoing eruptions. This may include the consequences of migration

7

away from volcanic areas, the adaptation of infrastructure, or changes to agricultural

practices.

Potential for high impact outcome

Analysis of SAR imagery, especially in combination with other remote sensing methods, has the

potential to provide data not available from other sources, which is useful to volcanologists, civil

protection authorities and disaster risk reduction practitioners. Publications arising from this project

will be published in international journals, and are expected to result in high impact publications. A

LiCSAR module that produces automatically generated SAR images suitable for change detection

would potentially be widely used by the remote sensing community with broad interests in

geohazards and other causes of land use change. It would also allow backscatter intensity

observations to be made routinely at thousands of sub-aerial volcanoes around the world.

Training

The student will work under the supervision of Dr Susanna Ebmeier in the Institute of Geophysics

and Tectonics volcanology group, Dr Mike Poland at the USGS and Prof Tim Wright (tectonics group

and head of COMET). The student will be trained in processing and analysing SAR intensity data

from a range of historical and current satellites as well as measuring deformation and topographic

change using interferometric methods. The student will be encouraged to expand their scientific

horizons by participating in training programmes supported by international volcanological and

geophysics networks such as IAVCEI and UNAVCO. The successful PhD student will have access to a

broad spectrum of training workshops put on by the Faculty of the Environment at Leeds

(http://www.emeskillstraining.leeds.ac.uk/).

Student profile

The student should be interested in remote sensing and volcanic hazard assessment, have good

quantitative data handling skills and be enthusiastic about learning and developing novel analysis

methods. An interest in communicating scientific results and international collaboration is also

desirable. The student should have a background in a quantitative science with some experience

and interest in scientific computing.

References

• Anderson, K. R., & Poland, M. P. (2016). Bayesian estimation of magma supply, storage, and

eruption rates using a multiphysical volcano model: Kīlauea Volcano, 2000–2012. Earth and

Planetary Science Letters, 447, 161-171.

• Arnold, D. W. D., Biggs, J., Wadge, G., Ebmeier, S. K., Odbert, H. M., & Poland, M. P. (2016).

Dome growth, collapse, and valley fill at Soufrière Hills Volcano, Montserrat, from 1995 to

2013: Contributions from satellite radar measurements of topographic change. Geosphere,

GES01291-1.

• Bovolo, F., & Bruzzone, L. (2005). A detail-preserving scale-driven approach to change

detection in multitemporal SAR images. IEEE Transactions on Geoscience and Remote

Sensing, 43(12), 2963-2972.

• Ebmeier, S. K., Biggs, J., Muller, C., & Avard, G. (2014). Thin-skinned mass-wasting

responsible for widespread deformation at Arenal volcano. Frontiers in Earth Science, 2, 35.

8

• Goitom, B, C. Oppenheimer, J. O. S. Hammond, R. Grandin, T. Barnie, A. Donovan, G.

Ogubazghi et al. "First recorded eruption of Nabro volcano, Eritrea, 2011." Bulletin of

volcanology 77, no. 10 (2015): 1-21.

• Meyer, F. J., McAlpin, D. B., Gong, W., Ajadi, O., Arko, S., Webley, P. W., & Dehn, J. (2015).

Integrating SAR and derived products into operational volcano monitoring and decision

support systems. ISPRS Journal of Photogrammetry and Remote Sensing, 100, 106-117.

• Pallister, J. S., D. J. Schneider, J. P. Griswold, R. H. Keeler, W. C. Burton, C. Noyles, C. G.

Newhall, and A. Ratdomopurbo. "Merapi 2010 eruption—Chronology and extrusion rates

monitored with satellite radar and used in eruption forecasting." Journal of Volcanology and

Geothermal Research 261 (2013): 144-152.

• Poland, M. P., & Carbone, D. (2016). Insights into shallow magmatic processes at Kīlauea

Volcano, Hawaiʻi, from a multiyear continuous gravity time series. Journal of Geophysical

Research: Solid Earth, 121(7), 5477-5492.

• Small, D. (2011). Flattening gamma: Radiometric terrain correction for SAR imagery. IEEE

Transactions on Geoscience and Remote Sensing, 49(8), 3081-3093.

• Wadge, G., Saunders, S., & Itikarai, I. (2012). Pulsatory andesite lava flow at Bagana

Volcano. Geochemistry, Geophysics, Geosystems, 13(11).

9

Active Tectonics & Fault Geomorphology around Major Cities of the Northern

Tien Shan

Supervisors: Dr John Elliott and Prof Tim Wright

School of Earth and Environment, University of Leeds

Project partner: Professor Richard Walker (University of Oxford)

Contact email: j.elliott@leeds.ac.uk

Mountains are created when continents collide, causing tectonic faults to move. Most faults are locked in the upper crust, slipping suddenly and catastrophically in earthquakes, and are part of the cycle of mountain growth (e.g. 2015 Gorkha earthquake, Nepal - Elliott et al. [2016]). An open question in the deformation of the continents is how strain (and therefore earthquake hazard) is distributed through the crust. Earthquakes are a natural hazard that are killing an increasing number of people, in part because populations are growing and densifying into urban centres (Crowley & Elliott, 2012). The recurrence time between earthquakes may be hundreds of years; many cities that are large today were small towns or did not yet exist when the last big earthquake struck (Campbell et al. 2015). Population centres are often clustered along mountain ranges, with cities lying next to faults that cause significant damage when they rupture due to the proximity of vulnerable buildings (Elliott et al. 2012). Over 50 capital cities of the Least Developed Countries in the world lie on top of faults in regions that are building up significant stresses within the crust (Figure 1). Furthermore, urban development in the intervening years has often hidden the expressions of the active earthquake faults beneath and around a city, making them harder to identify today (Mackenzie et al. 2016). By targeting cities along the Northern Tien Shan, this project will better characterise the active faulting and seismic hazard in this collision zone, and develop approaches that will be applicable to interpreting faulting geomorphology globally. This particular collision zone has had major earthquakes in the past, but is less well studied than many orogens.

Figure 1: The capital city of Kyrgyzstan (Bishkek, population 0.9 million), lies in the shadow of the Tien Shan mountains. It and similarly large cities along the Northern Tien Shan are exposed to the hazard posed by large

earthquakes. (image width 20 km, looking south, note mountains are vertically exaggerated 3x, rising over 4000 m above Bishkek). Image from GoogleEarth.

A recent explosion in the number of optical and radar satellite based platforms over the past decade, and their systematic acquisition strategies has provided a wealth of high resolution data with near-global coverage (Elliott et al., 2016b), which is available for tackling problems concerning

10

active tectonics, continental deformation, faulting and earthquake hazard (Wright et al. 2012). The launches of the Sentinel-1A and 1B radar satellites by the European Space Agency in 2014 and 2016, with an open access data policy, has provided the opportunity for earthquake monitoring and measurements of crustal deformation over wide areas (Elliott et al, 2015). Commercially operated optical imagery satellites can be tasked to acquire stereo images over fault zones from which we can generate high resolution topographic images at the metre scale for geomorphic analysis of fault scarps and quantitative derivation of fault offsets (Zhou et al. 2015), something not possible with the current openly available 30 metre resolution topography in many parts of the world. This project will make use of these latest satellite technologies to better characterise the faulting and strain accumulation along the northern Tien Shan.

Figure 2: Hillshaded Digital Elevation Model (1 metre) of the 2013 Balochistan (Mw 7.8 Pakistan) earthquake rupture (the rupture is unannotated on the left and marked by red lines on the right) derived from Pleiades

stereo satellite imagery (Zhou et al. 2015). Using these observations it is possible to derive quantitative measurements of the fault offsets and remotely interpret the rupture geomorphology and fault trace.

Objectives

In this project, the student will work with leading scientists at Leeds (John Elliott & Tim Wright) and the University of Oxford (Richard Walker) to apply the latest techniques in measuring active tectonics, faulting and landscape evolution to the northern extent of the Tien Shan orogen of central Asia. In particular, according to your particular research interests, the studentship could be initiated with analysis of:

1. Remote Sensing (DEMs and High Resolution Imagery) of the active tectonics of the northern Tien Shan: You will derive digital elevation models (DEMs) of parts of the faults around cities in the northern Tien Shan and produce orthorectified imagery using modern photogrammetry techniques applied to the latest high resolution optical satellite imagery (Zhou et al. 2015). From these data the student will identify potentially active faults in the landscape geomorphology both around and within cities. To aid this identification and additionally provide the workflow to potentially automate this with future global topographic datasets, you will implement strategies for the systematic estimation of landscape indices of fault activity based upon topographic slope and surface roughness. You will augment your findings with existing seismicity datasets and past earthquakes.

2. Strain Accumulation (InSAR Velocity Mapping) of faults around the large cities: regional scale velocity fields for the continental regions will be produced as part of the Looking inside the Continents from Space (LiCS) project with the Centre for the Observation and Modelling of

11

Earthquakes, Volcanoes and Tectonics (COMET http://comet.nerc.ac.uk/). This project will provide the opportunity to build upon these preliminary velocity fields by undertaking a more detailed study of strain accumulation in the immediate vicinity of cities along the Northern Tien Shan. This will make use of the Sentinel-1 data acquired since 2014 and throughout the timescale of the project to build up a long time series of deformation. This will enable estimation of current fault slip rates, and will involve analysis of Sentinel-1 InSAR data, mitigation of atmospheric noise (Walters et al., 2013) and potentially anthropogenic sources as well. The velocity fields will be augmented by the relatively sparse GPS for this region.

3. Fieldwork (Corroborate remotely-derived observations): There is the potential to undertake short periods of fieldwork to the northern Tien Shan, in order to verify the remotely derived observations of fault scarps on the ground, make higher resolution measurements with GPS and Structure from Motion (SfM) techniques (Mackenzie et al. 2016) and sample fault offsets for chronological dating (Campbell et al., 2015). This will enable comparison of long-term slip rates with those derived geodetically, as well as establish whether fault structures are active.

Potential for high impact outcome

Earthquake hazard is a pressing issue facing many developing nations. We are in a unique position at Leeds to bring together a range of observational approaches to answer important unresolved questions about the relative activity of faulting around cities distributed in major collisional orogens. The research topic has immediate relevance to improving estimations of seismic hazard in these less well studied regions, and we anticipate the project generating several papers. There will be ample opportunities to deliver the results of the project at international conferences in addition to UK meetings. Through in-country collaborators, there will be the opportunity to communicate the earthquake hazard to local authorities and civil protection planners.

Training

The student will work under the supervision of Dr John Elliott and Prof Tim Wright within the Tectonics group of the Institute of Geophysics & Tectonics in the School of Earth & Environment at Leeds. This project provides a high level of specialist scientific training in: (i) Satellite optical data, (ii) Data processing (iii) Landscape interpretation. Co-supervision will involve regular meetings with our Oxford partner through joint supervision by Prof Richard Walker, who has undertaken a number of field campaigns in this region (Abdrakhmatov et al. (2016), Campbell et al. (2015, 2013)), in addition to other active faulting zones. The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range from scientific computing through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). The student will also have the opportunity to engage with scientists within the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET http://comet.nerc.ac.uk/) at a range of other UK institutions who have a broad interest in problems of active tectonics and earthquakes.

Student profile

The student should have a strong interest in active tectonics problems, a strong background in a quantitative science (geophysics, earth sciences, physics), and a familiarity and willingness to develop their skills in scientific computing.

References

Abdrakhmatov, K. E., R. T. Walker, G. E. Campbell, A. S. Carr, A. Elliott, C. Hillemann, J. Hollingsworth et al. (2016) Multisegment rupture in the 11 July 1889 Chilik earthquake (Mw 8.0–8.3), Kazakh Tien Shan,

12

interpreted from remote sensing, field survey, and paleoseismic trenching, Journal of Geophysical Research, 121, 4615-4640, doi:10.1002/2015JB012763.

Campbell, G. E., R. T. Walker, K. Abdrakhmatov, J. L. Schwenninger, J. A. Jackson, J. R. Elliott & A. C. Copley (2013) Quaternary slip-rate, seismogenic potential and the role of strike-slip faulting in the northern Tien Shan region, Journal Geophysical Research, 118, 5681-5698, doi:10.1002/jgrb.50367

Campbell, G. E., R. T. Walker, K. Abdrakhmatov, J. A. Jackson, J. R. Elliott, D. Mackenzie, T. Middleton & J. L. Schwenninger (2015) Great earthquakes in low strain rate continental interiors: An example from SE Kazakhstan, Journal Geophysical Research, 120, 5507-5534, doi:10.1002/2015JB011925.

Crowley, K. & J. R. Elliott (2012) Earthquake disasters and resilience in the global North: lessons from New Zealand and Japan, The Geographical Journal, 178, 208-215, doi:10.1111/j.1475-4959.2011.00453.x.

Elliott, J. R., R. Jolivet, P. Gonzalez, J.-P. Avouac, J. Hollingsworth, M. Searle & V. Stevens (2016) Himalayan Megathrust Geometry and Relation to Topography Revealed by the Gorkha Earthquake, Nature Geoscience, 9, 174-180, doi:10.1038/NGEO2623.

Elliott, J. R., A. Copley, R. Holley, K. Scharer & B. Parsons (2013) The 2011 Mw 7.1 Van (Eastern Turkey) Earthquake, Journal Geophysical Research, 118, 1619-1637,doi:10.1002/jgrb.50117.

Elliott, J. R., R. J. Walters & T. J. Wright (2016) The role of space-based observation in understanding and responding to active tectonics and earthquakes, Nature Communications.

Mackenzie, D., J. R. Elliott, E. Altunel, R. T. Walker, Y. C. Kurban, J. L. Schwenninger & B. Parsons (2016) Seismotectonics and rupture process of the Mw 7.1 2011 Van reverse faulting earthquake, Eastern Turkey, and implications for hazard in regions of distributed shortening, Geophysical Journal International, 206, 501-524, doi:10.1093/gji/ggw158

Walters, R. J., J. R. Elliott, Z. Li, & B. Parsons (2013) Rapid strain accumulation on the Ashkabad fault (Turkmenistan): a robust slip rate estimate from MERIS-corrected InSAR data, Journal Geophysical Research, 118, 3674-3690, doi:10.1002/jgrb.50236.

Wright, T. J., J. R. Elliott, H. Wang & I. Ryder (2013) Earthquake cycle deformation and the Moho: Implications for the rheology of continental lithosphere, Tectonophysics,609, 504-523, doi:10.1016/j.tecto.2013.07.029.

Zhou, Y., J. R. Elliott, R. T. Walker & B. Parsons (2015) The 2013 Balochistan earthquake: an extraordinary or completely ordinary event?, Geophysical Research Letters, 42, 6236-6243, doi:10.1002/2015GL065096.

13

Magmatic volatile contents and storage time-scales for rift-related volcanism

in Ethiopia

Supervisors: Dr David Ferguson1, Dr Dan Morgan1, Dr Marie Edmonds2, Dr Tyrone Rooney3, Prof

Gezahegn Yirgu4 1School of Earth and Environment, University of Leeds 2University of Cambridge 3Michigan State University 4Addis Ababa University

Contact email: d.j.ferguson@leeds.ac.uk

This project will combine field-work at several volcanic centres in Ethiopia with state-of-the-art

geochemical analysis to better understand the generation, ascent and eruption of basaltic magmas

in the East African rift. Continental rifting in Ethiopia is accompanied by extensive magmatic and

volcanic activity, fuelled by melts generated in the sub-rift mantle. In addition to feeding numerous

volcanoes along the rift system, these magmas also play an important role in facilitating tectonic

extension of the lithosphere (e.g. Buck, 2006). In the Main Ethiopian Rift (MER), where rifting is

relatively advanced, there is a clear spatial link between the ascent and eruption of melts and

lithospheric tectonics, with volcanism and magma intrusion focussed along discrete zones of

extensional faulting (Hayward and Ebinger, 1996). Magma production here reflects the interplay

between asthenospheric dynamics (temperature, composition etc.) and decompression due to

lithospheric thinning, with the relative importance of these factors remaining a matter of debate

(e.g. Armitage et al., 2013). Following partial melting, these magmas travel upwards into the

lithosphere where the conditions of pre-eruptive storage and spatial patterns of volcanism at the rift

surface reflect the interaction of the ascending melts with lithospheric structures and stress fields

(Rooney et al., 2007, 2011).

A major gap in the current understanding of magmatic activity in Ethiopia is the lack of constraints

on the volatile contents of the magmas and their mantle source. Since the presence of volatile

components, such as H2O and CO2, strongly affects the melting behaviour of the mantle, constraints

on magmatic volatiles is essential to refining models of magma generation (e.g. Ferguson et al.,

2013) and ultimately for modelling the chemical and physical structure of the Ethiopian mantle (e.g.

Rooney et al., 2012) and the cycling of volatiles from the mantle to the crust/atmosphere. Variations

in the composition of magmas between different intra-rift zones of magmatic-tectonic extension

have been previously linked to changes in the local tectonics, influencing the maturity of magmatic

pathways and depths of crustal reservoirs (Rooney et al., 2007). However, thus far no detailed

studies have been undertaken to quantify the time-scales and depths of magma storage beneath

basaltic volcanoes in the MER and how this vary with local tectonic setting.

This project, through the development of exciting novel geochemical datasets for Ethiopian basalts,

will provide important new insights into the production and ascent of magmas erupted at

monogenetic cones in the MER. This will be done using the record of magmatic processes available

from melt inclusions trapped within olivine crystals and also from analysis of the olivine phenocrysts

themselves. The melt inclusion data will provide important information on the pre-eruptive volatile

contents and compositional diversity of basaltic magmas, illuminating the range of primary melt

compositions and allowing for an estimation of the concentrations of volatile elements in the mantle

source and the volcanic flux of volatiles from the mantle to the atmosphere. This will be combined

14

with studies of intra-crystal Fe-Mg diffusion to quantify residence timescales within crustal

reservoirs (e.g., Hartley et al., 2016), constraining the pre-eruptive histories of magmas and testing

whether these vary significantly in different part of the rift. Using these datasets, you will develop an

integrated ‘source-to-surface’ model of basaltic magmatism in the MER. You will receive experience

and training in a variety of field, laboratory and data analysis skills relevant to the study of volcanic

rocks and magmatic processes. This work will benefit from engagement with a large community of

multi-disciplinary scientists in the UK and elsewhere who are actively conducting research on

magmatism and rifting in Ethiopia, including the on-going NERC funded RiftVolc project.

Objectives

You will undertake fieldwork in Ethiopia to sample scoria deposits from several groups of

monogenetic volcanoes within the Main Ethiopian Rift. These will primarily target regions where

previous studies have indicated that variations in magmatic processes exist due to differences in the

local tectonic setting (e.g. Rooney et al., 2007). Olivine crystals separated from the scoria will be

assessed to identify those containing melt inclusions suitable for geochemical analysis and those

with intra-crystal Fe-Mg zonation suitable for diffusion modelling. The analytical/work programme

will involve:

1. Analysis of melt inclusions by secondary ion mass spectrometry (SIMS) to measure

concentrations of trace and volatile elements in the melt inclusion glass (most likely using

the NERC Ion Micro-Probe facility in Edinburgh).

2. Raman spectroscopy of melt inclusion bubbles to accurately quantify CO2 contents (e.g.

Moore et al., 2015).

3. Electron microprobe (EMPA) and electron back-scatter diffraction (EBSD) imaging and

analysis of olivine crystals to quantify intra-crystal Fe-Mg variations.

4. Diffusion modelling of the Fe-Mg data in the olivine crystals to extract quantitative time-

scale information for magma residence in the lithosphere.

5. Develop models for magma generation, ascent and storage at the study sites. This will

include new constraints on the flux of volatiles associated with basaltic magmatism in the

MER and can be integrated with other on-going geophysical and geochemical studies.

15

Figure 1: Basaltic fissure eruption in Ethiopia (Afar) in 2009. Scoria deposits formed around the vent during

explosive lava-fountaining activity contain loose olivine crystals, some of which contain melt inclusions. This

project will sample similar deposits from monogenetic cones in the MER (see Rooney et al., 2011).

Potential for high impact outcome

This project will increase understanding of volcanic processes in a region of extensive volcanic

activity where the development of new infrastructure (cities, roads etc.) is occurring at an often

rapid pace. This includes data on the timescales over which magmas feeding explosive basaltic

volcanoes reside in the crust prior to eruption. In scientific terms it will provide a significant

contribution to understanding magmatic processes in the MER, which is a natural laboratory for

studies of continental rifting. It will provide robust constraints on the volatile budget of MER

magmas, a vital parameter for understanding asthenosphere dynamics and to quantify volatile fluxes

from the rift zone. The results will have important implications for various on-going interdisciplinary

studies on continental rifting and have the potential to generate high-impact publications.

Training

The student will work under the supervision of Dr David Ferguson and Dr Dan Morgan in Leeds and

Dr Marie Edmonds in Cambridge. They will also interact with international co-supervisors from the

USA (Prof Tyrone Rooney, Michigan State University) and Ethiopia (Prof Gezahegn Yirgu, University

of Addis Ababa). They will gain high-level experience and expertise in: i) field sampling in volcanic

terrains; ii) preparation of samples for geochemical analysis; iii) data collection using a variety of

analytical instrumentation; and iv) diffusion modelling to extract quantitative timescale information.

Within SEE they will have the opportunity to engage with researchers in the volcanology, high-T

geochemistry and tectonics/geodynamics research groups, many of whom will have overlapping

interests with aspects of this work. They will also benefit from membership of NERC’s Centre for the

Observation and Modelling of Earthquakes and Tectonics (COMET), a collaboration between several

UK universities, and from interaction with the NERC funded RiftVolc project, which is focused on

volcanism in the MER and also involves researchers at several UK institutions. In addition, the

student will also have access to a broad range of Faculty- and University-led training courses and

workshops at Leeds (http://www.emeskillstraining.leeds.ac.uk/).

16

References

• Armitage, J. J., Ferguson, D. J., Goes, S., Hammond, J. O., Calais, E., Rychert, C. A., & Harmon,

N. (2015). Upper mantle temperature and the onset of extension and break-up in Afar,

Africa. Earth and Planetary Science Letters, 418, 78-90.

• Buck, W.R., 2006. The role of magma in the development of the Afro-Arabian Rift

System. Geological Society, London, Special Publications, 259(1), pp.43-54.

• Ferguson, D. J., Maclennan, J., Bastow, I. D., Pyle, D. M., Jones, S. M., Keir, D., ... & Yirgu, G.

(2013). Melting during late-stage rifting in Afar is hot and deep. Nature, 499(7456), 70-73.

• Hartley, M. E., Morgan, D. J., Maclennan, J., Edmonds, M., & Thordarson, T. (2016). Tracking

timescales of short-term precursors to large basaltic fissure eruptions through Fe–Mg

diffusion in olivine. Earth and Planetary Science Letters, 439, 58-70.

• Hayward, N. J., & Ebinger, C. J. (1996). Variations in the along‐axis segmentation of the Afar

Rift system. Tectonics, 15(2), 244-257.

• Moore, L. R., Gazel, E., Tuohy, R., Lloyd, A., Esposito, R., Steele-MacInnis, M., ... & Bodnar, R.

J. (2015). Bubbles matter: An assessment of the contribution of vapor bubbles to melt

inclusion volatile budgets. American Mineralogist, 100(4), 806-823.

• Rooney, T., Furman, T., Bastow, I., Ayalew, D., & Yirgu, G. (2007). Lithospheric modification

during crustal extension in the Main Ethiopian Rift.Journal of Geophysical Research: Solid

Earth, 112(B10).

• Rooney, T. O., Bastow, I. D., & Keir, D. (2011). Insights into extensional processes during

magma assisted rifting: Evidence from aligned scoria cones. Journal of Volcanology and

Geothermal Research, 201(1), 83-96.

• Rooney, T. O., Herzberg, C., & Bastow, I. D. (2012). Elevated mantle temperature beneath

East Africa. Geology, 40(1), 27-30.

17

Constructing geochemical analogues of the asthenosphere: Earth's largest

geochemical reservoir

Supervisors: Dr Jason Harvey , Dr Dan Morgan and Dr Thomas Mueller

School of Earth and Environment, University of Leeds

Contact email: feejh@leeds.ac.uk

Project synopsis

Figure 1. Serpentinized oceanic lithospheric mantle. But how representative is abyssal

peridotite like this of the convecting mantle as a whole, before it is hydrated? (from Bach et al.,

2004)

It is becoming increasingly clear that the study of basalt composition does not always lead to an accurate assessment of the isotopic and chemical composition of its mantle source. Therefore, in order to understand mantle composition better, it is more prudent to collect direct evidence from the mantle itself. However, obtaining representative samples of the modern-day convecting mantle is problematic because it is overlain by the lithosphere, yet lithospheric mantle samples are the only examples of the mantle available. Drilled or dredged abyssal peridotite is often heavily altered by interaction with seawater and hydrothermal fluids. On the other hand, peridotite xenoliths, while exposed at the surface of the Earth, are often affected by metasomatism, melt-rock interaction and / or refertilization processes. This project will examine the various processes that have affected the composition of peridotites recovered from the Mid-Atlantic ridge, the Iberian passive margin and the Cape Verde Islands in order to (i) better understand the processes that can overprint the chemical and isotopic signatures preserved in the upper mantle at different tectonic settings, and (ii) assess peridotite from each of these provinces for its suitability as a chemical and isotopic proxy for the more voluminous, yet unreachable, asthenospheric mantle. The project will employ a combination of petrology and isotope geochemistry in order to achieve these objectives. Critically, lithophile (Sr-Nd-Pb) and siderophile (Re-Os) element isotope systems will be used to untangle the effects of metasomatism, melt-rock interaction and refertilization.

Objectives

Two key questions can be posed: (i) Which of the chemical and isotopic heterogeneities observed in lithospheric mantle samples are representative of all of the mantle (i.e. the lithosphere and

18

asthenosphere) and which are only present in the lithosphere (i.e. are unlikely to contribute to the composition of asthenosphere-derived basalts) and (ii) in which source of lithospheric peridotite (abyssal peridotite vs. peridotite xenoliths) is it easiest to “see through” secondary chemical and isotopic “smudging” and provide a realistic representation of the composition of the asthenospheric mantle and the heterogeneities that are preserved within it?

Background

Figure 2. Peridotite from oceanic basins (abyssal peridotite) while only recently separated from the asthenosphere is often extensively altered by seawater – peridotite interaction, obscuring the composition of primitive melt depleted mantle (from Bach et al., 2004)

For over half a century the composition of the Earth’s mantle has been determined largely by indirect methods. These range from geophysical measurements, which identify large volumes of the mantle that have distinctly different physical properties to their immediate surroundings, to the composition of basalts, which traditionally have been assumed to be representative of the mantle domains that produced them through partial melting. Apart from fortuitous instances where the mantle is exposed, for example in orogenic massifs, in ophiolites and as peridotite xenoliths (accidently transported to the surface in alkali basalts), the majority of what we think we know about the composition of the mantle has, to date, been derived indirectly. Experimental petrology and geochemical modelling tell us about the behaviour of incompatible trace elements during partial melting in the mantle, allowing the prediction that peridotite and the lavas that it produces have complimentary elemental compositions. Moreover, because isotope ratios of elements are not fractionated during high temperature processes, it is assumed that the isotopic fingerprint of a mantle reservoir is reproduced in the melts that it produces. However, there is increasing evidence to suggest that it is not necessarily safe to make the assumption that these fingerprints are faithfully transferred from mantle source to basalt – the fingerprint is somewhat “smudged” as there are domains of varying sizes (cm to km) in the mantle that do not correspond to the composition of basalts they are inferred to have produced. Unfortunately, the mantle samples that we have to work with are exclusively from the lithospheric mantle – the asthenosphere, which contributes to the majority of intra-plate basalt petrogenesis is not accessible for direct sampling. Dredged or drilled abyssal peridotite is often heavily hydrated and its composition drastically altered through interaction with seawater and / or hydrothermal fluids, whereas peridotite xenoliths can be affected by cryptic metasomatism, melt infiltration and refertilization – all of which potentially obscure the primary nature of the original peridotite that it represented when melt was first extracted from it.

19

Samples

Figure 3. Melt-rock interaction in peridotite from the sub-continental lithospheric mantle overprints primary geochemical and isotopic melt depletion signatures. Only by “looking through” these secondary processes can we gain insight into the composition of Earth’s asthenosphere (from Harvey et al. (2010).

For this project Mid-Atlantic Ridge peridotites will be sampled from the extensive collections available to Harvey at Woods Hole Oceanographic Institution, Massachusetts and Scripps Institution of Oceanography, California. In addition, peridotite samples from the Iberian passive margin (Ocean Drilling Program Leg 173) will be also be selected from the IODP core repository in Bremen. These will be supplemented by field sampling of peridotite xenoliths from the Cape Verde Islands (in which the student will be involved), where primitive basalts have erupted through similar oceanic mantle to the other sample suites. The majority of the project will concern high-precision isotope geochemistry (Sr-Nd-Pb, Re-Os) to be performed in a clean laboratory environment at the University of Leeds. We are developing cutting edge techniques for the measurement of mantle sulphide grains and mantle minerals for e.g. Os and Pb isotopes in individual sulphide grains and high precision Sr and Nd isotope measurements on single clinopyroxene grains, and measurements of this nature will be a key element of the project. This work will complement ongoing work in this field already being undertaken at the University of Leeds by Harvey, Morgan and Mueller who have a strong track record in publishing high quality geochemistry research.

The ideal candidate

You will have a good degree in geology or a closely related area and have a strong interest in “hard-rock” sub-disciplines (igneous and metamorphic petrology, mineralogy, geochemistry) and preferably an interest in analytical techniques. Previous analytical experience would be an advantage, but is not essential. The project will mostly be laboratory based, but you will be expected to participate in fieldwork in the Cape Verde Islands

Training

The successful applicant will be trained in a wide range of cutting edge geochemical techniques involving sample preparation, purification and analytical methods. The measurements made will make full use of the facilities available within the School of Earth and Environment (secondary

20

electron microscope, electron probe microanalyser, inductively coupled plasma mass spectrometry (both with and without laser ablation) and thermal ionization mass spectrometry

Potential for high impact outputs

Challenging the fundamental tenet that mantle composition cannot be accurately assessed through the composition of the basalts that it produces has enormous potential to yield high impact outputs. Over the last few years the lead supervisor and co-workers have demonstrated that the Earth’s mantle is chemically and isotopically heterogeneous at cm to km scales and that this variability is not always expressed in the composition of basalt. The next stage of this research is to unequivocally separate the processes that introduce heterogeneity into lithospheric mantle from those that are likely affecting the inaccessible asthenospheric mantle i.e. which processes are the real control on geochemical and isotopic signatures during basalt petrogenesis and which, although clearly present in the lithospheric mantle, simply mask asthenosphere composition.

Further reading

• Bach et al. (2004) Geochem, Geophys, Geosys 5 (9). • Burton et al. (2012) Nat Geosci 5, 570-573. • Harvey et al. (2011) Geochim Cosmochim Acta 75, 5574-5596. • Harvey et al. (2012) J. Petrol 53, 1709-1742. • Harvey et al. (2015) Geochim Cosmochim Acta 166, 210-233.

21

Observing and modelling transient slip events on creeping faults

Supervisors: Dr Jessica Hawthorne1, Dr John Elliott1, Dr Richard Walters2, ProfessorTim Wright1

1School of Earth and Environment, University of Leeds 2University of Durham

Contact email: J.C.Hawthorne@leeds.ac.uk

Creeping faults accommodate most of their slip aseismically, often at average rates of a few cm per year, comparable to the speeds of plate motion. Friction on creeping faults is thought to be broadly velocity-strengthening---resistant to large increases in slip speed. And indeed, creeping faults are so far observed to host few to no large earthquakes (e.g., Johanson and Bürgmann, 2005; Lienkaemper et al, 2012). From a hazard perspective, creeping faults would then seem ideal, as they gradually slip to allow for large-scale plate motion.

However, there is at least one important aspect of creeping faults that we do not understand: transient slip events, or surface creep events (e.g., Gladwin et al, 1994; Rousset et al, 2016). In these intervals, the slip rates on portions of creeping faults increases by a factor of 10 to 1000 and remains high for a few minutes to a few days before decreasing back to rates smaller than the rate of plate motion. For instance, on the northern portion of the creeping section of the San Andreas Fault, highly periodic several-hour long surface creep occur every few months. These events account for most of the slip accumulated at this location, as seen in Figure 1 (e.g., Gladwin et al, 1994).

Figure 1: Creep events recorded at USGS creepmeter CWN, which records the surface displacement across the

fault. CWN is located near the northern end of the creeping section of the San Andreas Fault.

22

Figure 2: The creeping (red) and locked (orange) portions of the central San Andreas Fault. The creeping section hosts numerous small earthquakes and creep events but few large earthquakes.

Despite accounting for large fractions of the total slip, creep events have sometimes been considered relatively unimportant in the scheme of large-scale slip on creeping faults. Individual creep events are mostly small, and they occur at the surface, so one hypothesis is that creep events are just a small-scale phenomenon occurring in response to rainfall or atmospheric pressure variations. However, recent observations have shown that many creep events extend 4 or 5 km along the strike of the fault and to depths of 4 or 5 km---well into the seismogenic zone (e.g., Mencin, 2016). The apparently large extent of repeated creep events also forces us to reconsider physical models of their behaviour. What frictional property allows portions of the fault to accelerate to speeds well above plate rate but then stall long before into an earthquake? This question is a topic of vigorous debate in the context of slow slip events---much larger (several 100-km-long) creep events that occur at depth, on the plate interface below the seismogenic zone. A range of possible physical mechanisms have been put forward, including changes in pore pressure that restrict acceleration or constraints associated with the limited size of slipping patches (e.g., Segall et al, 2010; Wei et al, 2013). However, it remains unknown whether the physical processes allowing for transient slip events are the same for deep slow slip as for shallow creep events.

Creep events are of particular interest today because of the increasing availability of high-resolution GPS and InSAR data, which make it possible to identify, observe, and understand the behaviour of creep events.

Objectives

In this project you will

1. Explore several possible models of creep events,

2. Test and develop the models with existing creepmeter data, and

3. Constrain and compare more predicted properties of creep events using InSAR data.

23

Numerical and Conceptual Modelling

You will consider several frictional models of the evolution of slip in creep events. You may begin with a “standard” frictional model, often used to reproduce steady creep or earthquakes. However, the relatively slow slip rates in creep events suggest that you may quickly decide that a more complex frictional model is necessary. For instance, it has been hypothesized that fault zones expand as they shear. This expansion could reduce the pore pressure in the fault zone, which in turn can increase the effective normal stress and clamp the fault together, keeping it from slipping further (e.g., Segall et al, 2010).

Of particular importance in the models is the importance of asperities: portions of the fault that may be especially prone to episodic creep. We want to know whether the entire fault is somewhat unstable, or whether it's just a few locations that initiate the episodic slip. To test the importance of asperities, you may consider a range of questions, including:

1. whether creep events start quickly and decay, or grow at a steady rate,

2. whether the slip rate in creep events is simply related to the propagation rate,

3. whether events persistently start at the same place,

4. how often creep events are influenced by external loading.

Observations

Some of these questions can be addressed by comparing the models' propagation and slip rates with creepmeter and strainmeter observations. However, creepmeters measure slip only at a single location, so they provide limited information about the spatial extent of creep events. To better constrain the spatial extent and depth of creep events, you may use InSAR data to see the distributed deformation produced by the slip. Better constraints on the depth extent can feed back into the models and allow you to determine how much of the large-scale fault slip is influenced by creep events. In addition, the observations maypermit you to identify creep events at locations where creepmeters are unavailable, and thus to constrain the behaviour of a larger range of faults.

Training

In addition to specialist training, through Leeds and COMET you would be able to interact with a large number of scientists with expertise in a range of aspects of fault mechanics, including modelling and geophysical and geological observations. You will also have access to courses organized by the faculty and university (http://www.emeskillstraining.leeds.ac.uk).

Student profile

This project would be suited for a student with a background in geology, physical sciences, computer science, or engineering.

References

Johanson, I. A., and R. Bürgmann. 2005. “Creep and Quakes on the Northern Transition Zone of the San Andreas Fault from GPS and InSAR Data.” Geophysical Research Letters 32 (July): 14306.

Lienkaemper, James J, Forrest S McFarland, Robert W Simpson, Roger G Bilham, David A Ponce, John J Boatwright, and S. John Caskey. 2012. “Long-Term Creep Rates on the Hayward Fault: Evidence for Controls on the Size and Frequency of Large Earthquakes.” Bulletin of the Seismological Society of America 102 (1): 31–41. doi:10.1785/0120110033.

24

Mencin. 2016. “Shallow and deep creep events observed and quantified with strainmeters along the SAF in Parkfield and the NAF in the Maramara.” FaultLab workshop.

Rousset, Baptiste, Romain Jolivet, Mark Simons, Cécile Lasserre, Bryan Riel, Pietro Milillo, Ziyadin Çakir, and François Renard. 2016. “An Aseismic Slip Transient on the North Anatolian Fault.” Geophysical Research Letters 43 (7): 2016GL068250. doi:10.1002/2016GL068250.

Segall, Paul, Allan M. Rubin, Andrew M. Bradley, and James R. Rice. 2010. “Dilatant Strengthening as a Mechanism for Slow Slip Events.” Journal of Geophysical Research 115 (December): B12305. doi:201010.1029/2010JB007449.

Wei, Meng, Yoshihiro Kaneko, Yajing Liu, and Jeffrey J. McGuire. 2013. “Episodic Fault Creep Events in California Controlled by Shallow Frictional Heterogeneity.” Nature Geoscience 6 (7): 566–70. doi:10.1038/ngeo1835.

25

Probing magma plumbing systems beneath volcanic calderas in the

Galapagos Islands

Supervisors: Professor Andy Hooper, Dr Marco Bagnardi and Dr Susanna Ebmeier

School of Earth and Environment, University of Leeds

Contact email: a.hooper@leeds.ac.uk

Volcanic calderas are surface depressions that form by collapse of overburden into a subterranean magma reservoir during volcanic eruptions. They exist on the scale of kilometres to tens of kilometres and are associated with the largest eruptions ever to have occurred on Earth. Collapses are rare, with only seven cases ever having been documented. However, we can learn much about the current state of magma chambers beneath calderas systems by measuring deformation at the surface; pressure changes within magmatic systems lead to displacements of the surface, which can be measurable using techniques such as GPS and radar interferometry (InSAR) (Pinel et al, 2014).

Figure 1: Map of the western islands of the Galapagos Archipelago. Six volcanoes on Isabela and Fernandina islands have been actively deforming during the last decade, and three of them erupted. For each volcano, dates of the latest eruptions are reported. (Bagnardi and Amelung, 2012)

In the Galapagos Islands there are six volcanoes with calderas that have actively deformed in the last two decades. Fernandina volcano was the site of one of the largest caldera collapses in recent history (1968), with 350 m of subsidence of the caldera floor in a few days. This event, however, remains enigmatic because no large eruption was associated with the collapse.

Various studies have concluded the existence of shallow magma reservoirs a few kilometres beneath Fernandina and other Galapagos volcanoes with similar geometries to the calderas themselves (e.g. Bagnardi and Amelung, 2012). On the other hand, the most recent caldera collapse episode to have been observed, the 2014-2015 eruption/collapse at Bardarbunga volcano in Iceland, was associated with withdrawal of magma from much deeper, at around 12 km depth (Gudmundsson et al, 2016). However, deformation measurements in and around the caldera at Bardarbunga could equally well

26

be explained by withdrawal of magma from a shallow chamber at only a few kilometres depth; caldera ring faults effectively transfer the source of deformation upwards. This raises the question of whether other caldera systems, such as those in the Galapagos, may not be as shallow as previously thought.

In this project you will test the hypothesis that magma reservoirs in the Galapagos may be deeper than currently thought using a combination of deformation measurements and gravity measurements. Inflow of magma at deeper depths will have a smaller gravity signal than the magma inflow required at shallow depths to give the same deformation signal, allowing us to distinguish between the two. Based on this new understanding, you will then go on to develop and test models for the caldera collapse that occurred at Fernadina last century.

Figure 2: Schematic cross-section across Fernandina Islands and the underlying oceanic crust showing the inferred structure of the shallow magmatic system (Bagnardi and Amelung, 2012)

Objectives

You will work with leading scientists at Leeds and Ecuador to:

1. Measure deformation at Fernandina Volcano using radar interferometry (InSAR) and a repeated GNSS field campaign.

2. Measure gravity changes Fernandina Volcano in the Galapagos by means of a repeated gravity field campaign.

3. Model the magma plumbing systems constrained by both deformation and gravity data and test the hypothesis of deeper magma chambers than implied by deformation data alone.

4. Develop and test models for the caldera collapse event at Fernadina in 1968.

Potential for high impact outcome

Caldera collapses are associated with the largest of all volcanic eruptions, but are poorly understood due to the fact that they are rare. Constraints on the present-day plumbing systems beneath volcanoes with caldera systems, will contribute to our understanding of the causes of collapse and we expect at least one high impact publication from this research.

Training

You will work under the supervision of Prof Andy Hooper and Dr Marco Bagnardi within the Institute of Geophysics and Tectonics in the School of Earth and Environmental Sciences. You will also

27

become a member of the Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), which brings together experts from the Universities of Oxford, Cambridge, Leeds, Bristol, Reading, Liverpool and Newcastle and University College London (http://comet.nerc.ac.uk). Through COMET, you will have access to a range of training opportunities related to deformation monitoring and modelling, in addition to a broad spectrum of training workshops provided by the Faculty, from training in numerical modelling through to managing your degree and preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). You will also be actively encouraged to present work at conferences and to publish papers.

Student profile

The student should have a strong interest in earth sciences and a strong background in a quantitative science (e.g. earth sciences, maths, physics, engineering). Enthusiasm to carry out fieldwork in tough volcanic environments is also essential.

References

• Bagnardi, M., and F. Amelung (2012), Space-geodetic evidence for multiple magma reservoirs and subvolcanic lateral intrusions at Fernandina Volcano, Galápagos Islands, J. Geophys. Res., 117(B10), B10406.

• Gudmundsson MT; Jónsdóttir K; Hooper A; et al (2016) Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow, Science, 353.

• Pinel V; Poland MP; Hooper A (2014) Volcanology: Lessons learned from Synthetic Aperture Radar imagery, Journal of Volcanology and Geothermal Research, 289, pp.81-113.

28

Tracking and measuring volcanic plumes using drones

Supervisors: Dr Evgenia Ilyinskaya1, Dr Tjarda Roberts2, Dr Melissa Pfeffer3, Dr Barbara Brooks4, Dr Anja Schmidt1

1School of Earth and Environment, University of Leeds 2CNRS Orleans 3Icelandic Meteorological Office 4NCAS, University of Leeds

Project partner: Icelandic Meteorological Office (CASE), CNRS Orleans

Contact email: e.ilyinskaya@leeds.ac.uk

Volcanic plumes are very complex mixtures of volcanic and atmospheric gases and small aerosol particles, such as sulphate. Knowing the aerosol size distributions and its chemical composition (e.g. Ilyinskaya et al. 2010) are key requirements for assessing the environmental, climatic and human health impacts of volcanic emissions (e.g. Schmidt et al. 2011). The aim of this PhD project is to develop a new type of drone capable of measuring aerosol (mass and size distributions) in plumes from active volcanoes in order to better understand how volcanic plumes form and disperse in the atmosphere.

At many volcanoes the plume is very difficult to sample due to safety issues (Fig 1). Using drones is therefore an exciting new field of research, which is opening up important scientific opportunities. Airborne measurements allow several things that a ground-based set up does not, for example, measurements very close to the degassing vent (Fig 2), and vertical and longitudinal profiling of the plume. The longitudinal profiles are of particular interest as they can give new insights into how the plume composition changes between the volcanic vent and locations further downwind, in particular inhabited areas. Drone work on volcanic plumes has so far focussed predominantly on gas measurements (e.g. Fig 2), with relatively few attempts to measure aerosol particles.

Figure 1: The 2014-2015 Holuhraun eruption in Iceland was the largest gas-and-aerosol-rich eruption in Europe since the devastating Laki eruption in 1783-1784. In spite of its long duration, only a handful of aerosol measurements were collected due to the difficulties with reaching the plume: the hot plume was lofted high over ground, and the crater rim was inaccessible due to the flowing lava. The photo shows measurements being done using a helicopter hovering over the active vent. Photo: E Ilyinskaya

29

Aim of this project

In this project the student will equip a drone (fixed wing and/or copter) with a lightweight aerosol sensor, for example LOAC (Vignelles et al. 2016) or Alphasense. The project will involve testing of both the aerosol sensor and the drone. As part of the CASE studentship, the student will spend at least 3 months in Iceland at the Icelandic Met Office (the national volcano observatory). Actively degassing volcanoes in other parts of the world, such as Etna in Italy or Masaya in Nicaragua, will also be visited.

Figure 2: Drone testing at a volcanic geothermal area in Iceland. The drone is used to carry gas sensors into a high-temperature gas fumarole. Photo: Icelandic Meteorological Office

While aerosol measurements will be the primary focus of this work, the drone will also carry sensors for volcanic gases (e.g. SO2, CO2, H2S) as well as sensors for atmospheric temperature, pressure and humidity (which allows measurement of H2O). Combining aerosol and gas sensors on one drone platform allows to quantify the fractionation between the gas and aerosol phase inside the volcanic plume.

The field data from the drone will be interpreted in terms of both volcano and atmospheric processes. The aim will be to produce a highly novel plume ‘cross-section’ map of aerosol size distribution (which is not possible through ground-based or balloon-borne measurements). Combined with wind speed measurements, these observations can be used to estimate the aerosol emission flux, which is a key source parameter for dispersion models. The plume will also be tracked by the drone as it travels away from the volcanic vent, and the results will be interpreted in order to understand how plume composition changes with time, including the very important process of conversion of SO2 gas to sulphate particles.

The student will also have the opportunity to set-up and run dispersion and aerosol microphysics models to calculate the plume dispersion and predict the atmospheric and climatic effects of the volcanic emissions (e.g. Schmidt et al., 2011).

30

Objectives

The main objective of this project is to develop and evaluate a new instrument and methods that will allow measurements inside volcanic plumes that are otherwise inaccessible, and to track plumes as they move away from the volcanic vent. The project will be subdivided into four main parts:

1. Development of a suitable drone platform for carrying the aerosol and gas sensors, including selection and testing of sensors

2. Drone testing. First tests will be done in volcanic geothermal areas in Iceland at non-eruptive gas fumaroles. Fieldtrips will also be undertaken to other active volcanoes: in Iceland if an eruption occurs; in Sicily (e.g. Etna, Vulcano, Stromboli), and Nicaragua (e.g. Masaya).

3. Data analysis. Comparison of the 3D observations made by the drone to more ‘traditional’ methods (e.g. direct sampling, remote sensing). Use of relevant models (e.g. dispersion and aerosol microphysics) to simulate the field data.

4. Interpretation of the field data and modelling results to understand how the volcanic plume(s) move and change in time and space. Assess the implications for environmental impacts.

Potential for high impact outcome

Volcanic gas and aerosol pollution can cause huge impact on the environment and climate and this hazard has recently been included in the UK National Risk Register. However, there are still many uncertainties about the ‘source term’, i.e. what the emissions of volcanoes are actually like, and how they spread in the atmosphere. New and innovative measurements of volcanic plumes are needed to address these uncertainties.

This project directly addresses some of these unknown factors as it will develop a new ability to rapidly probe different parts of the volcanic plume and thereby provide new insights into how the volcanic plume behaves and evolves with time. This new technology is anticipated to become widely used, and to yield new insights into emissions and atmospheric dispersion of volcanic aerosol. When combined with atmospheric modelling, it will be possible to assess health hazards and climatic effects arising from volcanic plumes (e.g. Schmidt et al. 2011).

The facilities at the University of Leeds/NCAS, CNRS-LPC2E (Orleans, France) and the Icelandic Met Office (Reykjavik, Iceland) are very well equipped to carry out the proposed work on drone development. The Icelandic Met Office has already done successful work on equipping drones for gas measurements (Fig 2) and will provide an environment where drones can be flight-tested with little air space restrictions, which is vital for this project.

We anticipate the project generating at least three peer-reviewed papers (3* and 4*), as well as the above-mentioned new technology to become widely used to monitor volcanic plumes.

Training

The student will be based at the University of Leeds but will spend at least three months at the Icelandic Met Office (Reykjavik, Iceland) as part of the CASE partnership. They will also make research visits to CNRS-LPC2E (Orleans, France) several times during the project. The student is expected to undertake extensive fieldwork for flight-testing the drone - primarily in Iceland, but also at other actively degassing volcanoes worldwide.

The student will greatly benefit from the CASE partnership with the Icelandic Met Office as they will be experiencing the practical applications of volcanological research. Drone flight-testing can be done in Iceland with relatively little air control restrictions, which is essential for this project. In addition, at the Icelandic Met Office the student will have the opportunity to take part in real-time volcano monitoring and multiple fieldtrips to Iceland’s active volcanoes.

31

The project supervisors are a wide-ranging team of experts assembled to fully support the interdisciplinary nature of this project. E. Ilyinskaya (IGT Leeds) is an expert in volcanic aerosol chemistry and in-situ sampling techniques with an extensive field experience from volcanoes worldwide, in particular in Iceland. T. Roberts (CNRS-LPC2E Orleans) is an expert in in-situ real-time volcanic gas and aerosol sensing and volcano plume chemistry processing. M. Pfeffer (IMO, Iceland) is the leading scientist for volcanic gas monitoring, including drone work, in Iceland. B. Brooks (NCAS Leeds) will provide leading expertise in development of drones for near-volcano measurements and draw on the extensive experience within NCAS in field measurement and the operation of drones in extreme conditions. A. Schmidt (ICAS Leeds) is an expert in volcanic gas and aerosol modelling using a wide range of numerical models.

Specialist training will be provided in: (i) Drone engineering, and flight controls; (ii) Techniques of gas and aerosol measurements (optical and direct sampling); (iii) Field work at active volcanic sites; (iv) complex 4D (3D space plus time) analysis of the real-time measurement data; (v) numerical modelling and data analysis. The student will become a member of the Volcanology group at Leeds. For the numerical modelling, further training and support will be provided by the newly founded Centre of Excellence in Atmospheric Modelling and the student has the opportunity to spend time at the UK Met Office who are responsible for operational forecasting of volcanic plumes in the UK air space.

The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of training workshops in numerical modelling, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

References

Ilyinskaya, E., C. Oppenheimer, T.A. Mather, R.S. Martin and P.R. Kyle (2010), Size-resolved chemical composition of aerosol emitted by Erebus volcano, Antarctica, Geochemistry Geophysics Geosystems, 11, Q03017, doi:10.1029/2009GC002855

Schmidt, A. et al. (2011): Excess mortality in Europe following a future Laki-style Icelandic eruption, Proceedings of the National Academy of Sciences, 108, 38, 15710-15715.

Vignelles D, Roberts TJ, Carboni E, Ilyinskaya E, Pfeffer M, Dagsson Waldhauserova P, Schmidt A, et al. (2016) Balloon-borne measurement of the aerosol size distribution from an Icelandic flood basalt eruption, Earth and Planetary Science Letters, 453, 252-259

32

Building a realistic model of Earth's magnetic field using constrained

dynamics

Supervisors: Dr Phil Livermore1and Dr Jitse Niesen2

1School of Earth and Environment, University of Leeds 2School of Mathematics, University of Leeds

Contact email: p.w.livermore@leeds.ac.uk

Background

A proper understanding of how the geomagnetic field is generated in Earth’s liquid core, by the so-called geodynamo, remains one of the greatest outstanding problems in Earth science. The principal difficulty is that the core is far too remote to be probed directly; scientific knowledge has advanced through exploiting the limited set of observations and computer simulations of the Earth’s core. Of significant importance is that observations from Earth’s surface can only constrain the structure of the magnetic field at the edge of the source region: the structure of the field within the core is unknown.

Figure 1: Observations of the Earth’s internal field taken from the surface and above constrain the structure of the field at the edge of the source region (the core-mantle boundary), shown by selected field lines. The sign of the outwards pointing magnetic field on the core-mantle boundary is shown as red/blue. The structure of the magnetic field inside the core is unknown, and is the focus of this project.

From a mathematical standpoint, on medium to long time scales, the core can be realistically modelled as a constrained dynamical system. Such an idea may be more familiar in mechanical systems such as (industrial) robots, which are often modelled as constrained dynamical systems: the parts move under the force exerted by motors according to the laws of mechanics under the constraint that the rods and other elements do not extend or compress. The rods in such systems can also be considered as springs in the limit that the stiffness constant goes to infinity. Specialized numerical methods are required when simulating such systems. The focus of this project is to consider the Earth's core as evolving under the control of a system of constraints, called the Taylor constraints (Taylor, 1963), which stem from the dominance of the rotational forces inside the core. In addition, recent evidence from seismology alongside studies of the material conditions thought to prevail within the core, further suggest the outermost part of the core is stratified (Davies et al, 2015). This leads to a further set of Malkus constraints, that add to the Taylor constraints, which the internal magnetic field must satisfy (Malkus, 1979). The goal of this project is to construct both static and dynamical models of the Earth’s magnetic field that satisfy this large set of constraints.

33

Realistic modelling of the large-scale background structure of the internal magnetic field may shed light on fundamental features which are still unexplained, such as why the Earth’s field is predominantly aligned with the rotation axis, and how the magnetic field undergoes global reversals.

Objectives

The goal of the project is to create realistic models of the magnetic field inside the Earth’s core, by exploiting the large family of the Taylor and Malkus constraints taken together. This project will involve both theoretical and computational aspects in modelling the Earth’s geodynamo as a constrained dynamical system. The project will be undertaken in two phases: observational snapshots models, and dynamical modelling.

1. In the first phase, the student will reproduce existing work on the mathematical structure of the Taylor constraints within a discretised model. Coupled with observations of the magnetic field, these can be used to infer the structure of the internal field inside the core (Livermore et al, 2011). A new analysis of the mathematical structure of the Malkus constraints will then allow the whole problem to be formulated. The main task will then be to find solutions of these nonlinear constraints which are also compatible with magnetic observations. This will allow us to image the magnetic field structure inside the core assuming stratification. The student will then compare such images to those deduced from other means (e.g. data assimilation).

2. The student will investigate magnetic field evolution within the stratified layer by constructing models that evolve subject to the Malkus constraints. These models will be compared to observation-derived models, as well as the state-of-the-art supercomputer models of Earth’s core.

Milestones

Year 1: Familiarisation with geomagnetic data and theory of the dynamics within Earth’s core. Formulation of the Taylor constraints within a discretised model. Benchmarking against existing results.

Year 2: Formulation of the new Malkus constraints. Using these alongside the Taylor constraints to image the magnetic field inside Earth’s core. Comparison to other models.

Year 3: Dynamical modelling and comparison to observations and simulations.

Potential for high impact outcome

Explaining important features in the Earth’s magnetic field is an international endeavour and of wide interest. Studies of models of the dynamics of Earth’s core date back to the 1950's and have been published in high impact journals such as Nature and Science. Imaging inside the Earth’s core would be paradigm changing.

Training

The student will learn both the theory and computational techniques required to model the Earth’s core, and will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of workshops in numerical modelling, through to managing your degree, to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

The student will be a part of the deep Earth research group, a vibrant part of the Institute of Geophysics and Tectonics, comprising staff members, postdocs and PhD students. The deep Earth group has a strong portfolio of international collaborators which the student will benefit from.

Although the project will be based at Leeds, there will be opportunities to attend international conferences (UK, Europe, US and elsewhere), and potentially collaborative visits within Europe.

34

Requirements

We seek a highly motivated candidate with a strong background in mathematics, physics, computation, geophysics or another highly numerate discipline. Knowledge of geomagnetism is not required, and training will be given in all aspects of the PhD. For further information please contact Phil Livermore (p.w.livermore@leeds.ac.uk) or Jitse Niesen (jitse@maths.leeds.ac.uk).

Other opportunities

The Deep Earth Research Group in Leeds (http://www.see.leeds.ac.uk/research/igt/deep-earth-research/) is one of the largest groups of scientists studying the structure and dynamics of Earth’s core and mantle in the world. Research topics include the dynamics and structure of the Earth’s magnetic field and convection in the outer core, material properties under high pressure and temperature and Global Seismology. The Group collaborates closely with the Department of Applied Mathematics in Leeds and Deep Earth research groups worldwide. Dr Livermore is interested in the dynamics of the core and geomagnetism. Please contact him (p.w.livermore@leeds.ac.uk) to discuss further PhD opportunities.

References

• Davies, C., Pozzo, M., GUBBINS, D., and Alfè, D. (2015). Constraints from material properties on the dynamics and evolution of Earth’s core. Nature Geoscience, 8(9), 678–685. http://doi.org/10.1038/ngeo2492

• Hulot, G., Sabaka, T. J., Olsen, N. and Fournier, A. (2015) The Present and Future Geomagnetic Field. Treatise on Geophysics, Vol 5.02, Elsevier.

• Livermore, P. W, Ierley, G. and Jackson, A. (2009). The construction of exact Taylor states. I: The full sphere. Geophysical Journal International, 179(2), 923–928. http://doi.org/10.1111/j.1365-246X.2009.04340.x

• Malkus, W. (1979). Dynamo macrodynamics in rotating stratified fluids. Physics of the Earth and Planetary Interiors, 20(2-4), 181–184.

• Stern, D. A Millennium of Geomagnetism, online material: http://www.phy6.org/earthmag/mill_1.htm

• Taylor, J. (1963). The Magneto-Hydrodynamics of a Rotating Fluid and the Earth's Dynamo Problem. Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 274, 274–283.

35

The evolution of porphyry-epithermal gold systems using trace element

mobility and concentration

Supervisors: Dr Dan Morgan, Dr David Banks, Dr Rob Chapman, Dr Steven Stackhouse

School of Earth and Environment, University of Leeds

Contact email: d.j.morgan@leeds.ac.uk

There is a significant amount of effort associated with understanding the genesis and evolution of copper- gold (Cu-Au) porphyry systems and their associated epithermal expressions, due to their commercial importance based on dual commodities, (e.g. Halter et al. 2002, Kessler et al. 2002, Williams-Jones and Heinrich, 2005)) . Consequently, this mineralisation is frequently well characterised at a regional and deposit scale. However, the strong association of critical elements such as Palladium (Pd), (Tarkian and Strybny, (1998), Thompson et al., (2002)), Selenium, (Se) or Tellurium (Te)) in parts of the mineralised system, (Fig 1) is poorly understood. Variability of trace elements and ligands may point to variability in the physico-chemical state of the mineralising system which affects transport and deposition of the economic metals. The trace element composition of Cu-Au porphyry-epithermal systems may also be related to the tectonic environment and initial state of the intrusions. This project provides an opportunity to address questions of trace element mobility and concentration within evolving magmatic hydrothermal systems. A key principle underpinning this study is that much as minor and trace elemental analysis has revolutionised the interpretation of igneous geological systems since the 1960's, such analysis has not yet been applied to mineralised systems such as Cu-Au porphyries.

Figure 1, Examples of minor element assovciations in Cu-Au porphyries. left: temagamite (Pd3HgTe3) (white) in chalcopyrite, Afton alkalic Cu-Au porphyry, BC, Canada. right: Gold particle coated with Bi telluride, Nucleus

porphyry, Yukon, Canada.

Objectives

This project focuses on three questions:

1. What are the trace elemental signatures associated with magmatic hydrothermal gold mineralisation?

2. What can they tell us about the evolving chemical environment during ore genesis?

3. Which other (often critical) metals can be co-genetic with gold, and what are the controlling factors in their enrichment?

36

Approach

This study will investigate a suite of samples of in-situ gold mineralisation across the porphyry-epithermal transition. Specific case studies could include Canadian alkalic and calc-alkalic porphyry systems such as Copper Mountain, BC Canada, (e.g. Fig 2), the Klaza porphyry-epithermal transition (Yukon, Canada) or porphyry-epithermal systems in Europe. Studied systems will be characterised in terms of fluid evolution and associated mineralisation using a raft of techniques including petrography, electron microscopy, electron beam microanalysis, fluid inclusion analysis and trace elemental analysis. In addition, the project will apply laser ablation ICP-MS to Au grains to inform trace element partitioning in the first systematic study of its kind. Questions of elemental mobility, speciation, partitioning and the sequence of enrichment, mobilisation and deposition events within the porphyry systems will be addressed, to establish the physico-chemical controls of both ore and trace element distribution.

Figure 2 Copper Mountain Cu-Au porphyry, British Columbia

This project in particular considers a broad-spectrum analysis of trace element abundances in natural gold particles forming from hydrothermal fluids. In examining changes in trace element abundances from field and fluid perspectives, a P-T-X view of the mineralising system will be attained. The study of trace element behaviour provides opportunity to develop new insights into the fluid evolution and associated mineralisation of complex but economically important hydrothermal systems, and to create powerful tools for understanding their origins. There exists a further possibility to use some ab-initio modelling to gain a different perspective on the behaviour and speciation of ions in solution.

Potential for high impact

The project addresses the fundamental behaviour of elements within porphyry hydrothermal systems and as such will generate new understanding which may find application in many areas;

1. Improved targeting of mineralised environments which have the potential to yield critical metals as by products,

2. Development of analytical expertise applying LA-ICP-MS to Au alloy within implications for enhanced ‘fingerprinting’ of gold from different environments, This expertise could find application in diverse fields including gold provenancing (for ethical or archaeological

37

purposes), and exploration, where the detailed trace geochemistry of gold specific to particular environments could aid exploration. This aspect builds on an existing large body of work undertaken at Leeds.

3. New understanding of trace element partitioning will aid interpretation of surficial samples routinely collected during reconnaissance exploration

Training

Candidates will benefit from a range of academic expertise in analytical techniques, ore deposit geology, geochemistry and igneous petrology. Specifically the student will gain:

1. Analytical skills, (LA-ICP-MS, SEM, EMP, fluid inclusion studies)

2. Core geological skills: (RL and TL microscopy,)

3. Field skills, (sample collection, logging)

4. IT skills: (ARC-GIS, Iogas, Leapfrog).

The candidate will undertake field studies in Canada and possibly Turkey, with all the associated implications for future employability. A field season of two summer months is standard for such work.

In addition, a wide range of training will be provided by the Faculty of Environment (http://www.emeskillstraining.leeds.ac.uk/). The broad spectrum of geological sciences represented in the project will provide the student with various possibilities to develop teaching skills through contribution to teaching as a demonstrator in both lab-based classes and on field courses. Research findings will be disseminated through presentations at both national conferences (e.g..MDSG) and international conferences, some of which are industry facing, such as the Vancouver Exploration Roundup. In this way the student will have access to first class networking opportunities in both academia and industry during their postgraduate career. The publishable outputs will include contributions to the flagship ore deposits literature (Economic Geology, Mineralium Deposita) , but the multidisciplinary nature and novelty of the research will also generate outputs for high impact journals such as Nature Geoscience and Geology.

The student will join a small team of ore deposits facing postgraduate students whose interests span critical metals, and Au formation in mineralisation associated with orogens. He/she will play a full role within the Ores and Minerals Group in IAG which holds regular in house academic seminars and benefits form a strong association with the SEG Chapter.

References

• Halter, W. E., Pettke, T., Heinrich, C.A 2002 The Origin of Cu/Au Ratios in Porphyry-Type Ore Deposit Science, v. 296 no. 5574, pp. 1844 1846

• Kesler, S. E., Chryssoulis, S. L. , Simon, G., 2002. Gold in porphyry copper deposits: its abundance and fate. Ore Geol Rev 21: p103–124

• Tarkian, M. and Stribrny, B., 1999. Platinum-group elements in porphyry copper deposits: a reconnaissance study. Mineralogy and Petrology, v.65 p. 161-183

• Thompson, J.F.H., Lang, J.R., and Stanley, C.R., 2002, Platinum group elements in alkaline porphyry deposits, British Columbia: British Columbia Ministry of Energy, Mines and Petroleum Resources, Exploration and Mining in British Columbia-2001, p. 57–64.

• Williams –Jones, and A.E., Heinrich, C.A., 2005. Vapor Transport of Metals and the Formation

of Magmatic-Hydrothermal Ore Deposits. Economic Geology 100, 7, p. 1287-1312.

38

Fixing the fossil record! Experimentally decrypting the altered isotope archive

preserved in ancient carbonates

Supervisors: Dr Thomas Mueller, Dr Tracy Aze, Dr Sandra Piazolo

School of Earth and Environment, University of Leeds

Contact email: t.mueller@leeds.ac.uk

This intriguing PhD project will experimentally explore the effects of chemical alteration processes experienced by the fossil and surrounding rock matrix during sedimentation. This geological record provides a direct source of information about the Earth system during greenhouse climates, which

can be used to better constrain future predictions of climate change. The student will use a combination of various experimental techniques, state-of-the-art analytical methods and numerical

modelling to quantify rates and mechanisms of the chemical alteration processes.

The geological record provides a direct source of information about the Earth system during greenhouse climates, which can be used to better constrain future predictions of climate change. The ratios between different elements and stable isotopes recorded in the shells of planktonic foraminifera have been demonstrated to reflect ambient water chemistry and temperature (Fig. 1). One of the most important tools for generating records of past climate is the oxygen isotope ratio (δ18O) of foraminiferal calcite. The δ18O is primarily controlled by the isotopic ratio of the water in which the calcite is precipitated and the temperature in which precipitation occurs with more negative δ18O values indicating warmer temperatures for calcite growth. Consequently chemical analysis of fossilised foraminifera provides a direct source information about ancient climates as far back as 100 million years ago. However, the robustness and accuracy of these key records can be compromised by alteration of sediments limiting their application to a restricted number of well-preserved samples (Fig. 1).

Similarly, magnesium isotopes in carbonate minerals were proposed as sensitive geochemical tracers for possible sources and sinks in low temperature aqueous systems (Higgins & Schrag 2010) as well as potential tracers for seawater chemistry through the Earth’s history (Eisenhauer et al. 2009). Stable Mg-isotopes may also be a sensitive tracer of the diagenetic history of hydrothermal dolomites that form in the early diagenetic and deep burial environment (Lavoie et al. 2014; Geske et al. 2012). However, due to the effects of dissolution, precipitation, diagenetic resetting and non-equilibrium fractionation processes, hydrothermal dolomites show a wide range of Mg-isotopic values, and there is still a lack of experimental data on Mg-isotope fractionation behaviour under reaction conditions representative of the burial diagenetic environment.

The major problem in using the isotope archive measured in ancient carbonates is that there is currently no quantitative assessment of the mechanisms and rates modifying the geochemical records in carbonates.

The motivation of this project is therefore to experimentally quantify the post-depositional mechanisms and rates of change of the chemical signatures recorded in fossil calcite that are used to generate records of past climates. The results will improve the accuracy of geochemical data interpretation and will provide a framework of predicted isotopic alteration of marine fossils based on depositional environments, burial histories and sediment composition by addressing three main questions:

1. What are the mechanism and rates of element and isotope exchange of structure forming (Ca-Fe-Mg-Ba-C-O) and trace elements (Fe, Mn, Ba, Sr) in carbonates?

2. What parameters are controlling element and isotope transport in carbonates under various conditions?

39

3. Which are the most suitable elements or isotopes to be used as palaeo-proxies and which are useful to extract kinetic, i.e. time information of geological processes?

Figure 1: Cross plots of multiple-specimen carbon and oxygen stable isotope data from planktonic foraminifera. A) The coloured ovals represent the average carbon and oxygen isotopic signatures of planktonic foraminifera

calcite from different tropical ecologies. B) Multiple-specimen carbon and oxygen isotopic values of tropical Eocene planktonic foraminifera. Above the dashed line are data from “glassy” specimens and below the dashed line are data from altered “frosty” specimens. The different symbols represent the same species, from the same

time period but with the different preservation histories which show a clear shift in oxygen isotope values between the two data sets. Figure modified from: A) (Pearson et al. 2007) and B) (Edgar et al. 2015)

Objectives

In a recent studies of our group, we presented the first results investigating the replacement reaction of single calcite crystals to form Mg-carbonates aiming to simulate dolomitization processes during burial diagenesis (Fig. 2). We have shown that rates of carbonate reactions depend on the effective element flux and control both the phase petrology and the spatial chemical composition of the reaction product. The same experimental approach can now be used to test, whether isotope exchange is coupled to the reaction front or whether isotope exchange is independent of the reaction progress. Detailed knowledge on these parameters allows to predict the element and isotope signatures preserved in natural geological settings and allow thus to reconstruct the temporal evolution more accurately (see review of (Müller et al. 2010) for details). We firmly believe that the next challenge to read the mineral archive preserved in its spatial chemical composition is to quantitatively investigate element and isotope exchange processes.

Figure 2: BSE and schematic model of calcite replacement by layered reaction rims (Jonas et al. 2015). The replacement reaction mechanism is dissolution-precipitation, but the reaction progress is controlled by diffusion of elements in the pore fluid resulting in a compositional zoning of the reaction rim.

The isotope exchange reaction accompanying the recrystallization process will be experimentally simulated by parameter variation to extract quantitative information on the chemistry and

40

microstructural evolution, i.e., transformation from a pristine “glassy” to an altered “frosty” textures and the isotope exchange between foraminifera, carbonate matrix and fluids. The diagenetic recrystallization process is mainly controlled by: 1) temperature, 2) composition of the sediment, 3) composition of the pore fluids, and 4) the rate at which the fluid is flowing through the rock. Therefore, the student will conduct experiments using synthetic rocks composed of selected fossil species with distinct isotope composition being embedded in a calcite ±clay matrix to systematically study the effect and dependence of these four parameters.

In this project, the student will work with experienced scientists at Leeds and their international collaborators to experimentally investigate carbonate reactions under diagenetic conditions.

The successful student will:

Carry out experiments to establish quantitative relationships between temperature, salinity, pH and redox conditions describing the kinetically controlled isotope exchange between carbonates (of different type/composition) and surrounding fluid phase in a polyphase setting (foraminifera and carbonate matrix in the presence of fluids).

Determine the microscopic processes governing the textural alteration of foraminifer shells.

Assess whether the rate of isotope exchange is independent of, or coupled to the textural replacement process.

Test whether presence/absence of clay minerals only affects the amount of available pore fluid or whether they enhance or retard the carbonate recrystallization process.

The School of Earth and Environment at Leeds has all the lab facilities needed for this project and the proposed experiments will build on our previous studies on carbonate replacement (Jonas et al. 2015). This setup investigates mineral/rock-water interaction at diagenetic conditions using 1-atm furnaces (with or without controlled fO2) and rapid-quench cold seal apparatus. The setup has been successfully proven to allow for a temporal monitoring of the reaction progress combining analysis of the fluid and solid phases using various state-of-the-science techniques.

Potential for high impact outcome

The project will focus on oxygen and, partly, carbon isotope systems to produce a comprehensive set of quantitative data describing the rate isotope exchange as a function of temperature, fluid composition, the flow rate and matrix composition. The results will provide the framework to extend the study to other commonly used geochemical proxies such as Ca, Mg, Sr, Nd, and B. Recent studies, partly driven by our group (Jonas et al. 2015; Müller et al. 2010; Müller et al. 2012; Mueller et al. 2014), emphasized the role of effective element fluxes on recorded compositional profiles. Likely, this will also affect isotope signatures which are typically used as environmental proxies given that reaction rates of minerals in the crust are, to a specific extent, directly linked to changes in the atmosphere and biosphere. This is in particular true for carbonates as they are a major source and sink of the Earth CO2 budget. A quantitative understanding on the effect of reaction and exchange kinetics on isotope composition of carbonates is crucial to evaluate the robustness of those isotope signatures for its correct interpretation.

The laboratory facilities at Leeds are extremely well equipped to carry out the proposed research, in particular due to the recent add-on of an experimental petrology laboratory. In combination with the superb analytical facilities of the low temperature geochemistry group (Cohen) and the high resolution TIMS and electron optics lab, this infrastructure provided by the School of Earth and Environmental Sciences, makes the University of Leeds one of the unique places at which this project can be successfully achieved. Given the high interest of using stable isotope composition of carbonates as tracer of paleo-conditions, we anticipate the project generating several publications being suitable for submission to a high impact journal with the potential of becoming 4* contributions.

41

Training & Framework of the project

In this interdisciplinary project the student will work under the supervision of Dr Thomas Müller (IGT), Dr Tracy Aze (ESSI) and Dr Sandra Piazolo (IGT) within the School of Earth and Environment. In addition, depending on the focus of interest of the PhD candidate the project offers and highly encourages the close collaboration with the Cohen research group being part of the ESSI within the School of Earth and Environmental Sciences. This project provides a high level of specialist scientific training in: (i) experimental techniques to study element/isotope transport including experiments with gas-mixing furnaces, cold seal and piston cylinder apparatus and flow-through reactor vessels; (ii) State-of-science analytical methods on the micro to nano-scale (SIMS, TIMS, LA-ICP-MS and RBS); (iii) numerical modelling (finite differences) in multiple programming environments.

The project provides possible interaction with the DFG funded “research priority group” CHARON working on mechanisms, rates and geological implications of carbonate proxies and alteration reactions.

In addition, the successful PhD student will have access to a broad spectrum of training in various analytical and experimental techniques, managing your degree, and preparing for your viva either by the Faculty (http://www.emeskillstraining.leeds.ac.uk/) or within collaborations in the UK and/or abroad. Moreover, research results will be presented at national & international meetings to integrate the student in the scientific community working in the field of paleo-proxies, and reactive mass transport.

Student profile

The student should have a minimum of an upper 2:1 degree (or international equivalent) and strong interest in experimental and analytical work, geochemical processes, and ideally paleoclimate research. A strong background in quantitative science (maths, physics and chemistry) and curiosity for interdisciplinary research is desired. Willingness to work within a research team is essential.

References

• Edgar, K.M. et al., 2015. Assessing the impact of diagenesis on δ11B, δ13C, δ18O, Sr/Ca and B/Ca values in fossil planktic foraminiferal calcite. Geochimica Et Cosmochimica Acta, 166, pp.189–209.

• Eisenhauer, A., Kisakürek, B. & Böhm, F., 2009. Marine calcification: an alkali earth metal isotope perspective. Elements, 5(6), pp.365–368.

• Geske, A. et al., 2012. Impact of diagenesis and low grade metamorphosis on isotope (?? 26Mg, ?? 13C, ?? 18O and 87Sr/ 86Sr) and elemental (Ca, Mg, Mn, Fe and Sr) signatures of Triassic sabkha dolomites. Chemical Geology, 332-333, pp.45–64.

• Higgins, J.A. & Schrag, D.P., 2010. Constraining magnesium cycling in marine sediments using magnesium isotopes. Geochimica et Cosmochimica Acta, 74(17), pp.5039–5053.

• Jonas, L. et al., 2015. Transport-controlled hydrothermal replacement of calcite by Mg-carbonates. Geology, 43(9), pp.779–783.

• Lavoie, D., Jackson, S. & Girard, I., 2014. Magnesium isotopes in high-temperature saddle dolomite cements in the lower Paleozoic of Canada. Sedimentary Geology, 305, pp.58–68.

• Mueller, T. et al., 2014. Diffusive fractionation of carbon isotopes in γ-Fe: Experiment, models and implications for early solar system processes. Geochimica et Cosmochimica Acta, 127, pp.57–66.

• Müller, T., Cherniak, D. & Bruce Watson, E., 2012. Interdiffusion of divalent cations in carbonates: Experimental measurements and implications for timescales of equilibration

42

and retention of compositional signatures. Geochimica et Cosmochimica Acta, 84, pp.90–103.

• Müller, T., Watson, E.B. & Harrison, T.M., 2010. Applications of Diffusion Data to High-Temperature Earth Systems. Reviews in Mineralogy and Geochemistry, 72(1), pp.997–1038.

• Pearson, P.N. et al., 2007. Stable warm tropical climate through the Eocene Epoch. Geology, 35(3), pp.211–214.

43

Seismic detection of hidden primordial regions in the Earth's lowermost

mantle

Supervisors: Dr Andy Nowacki1, Dr Sebastian Rost1 and Dr Mike Thorne2

1School of Earth and Environment, University of Leeds 2University of Utah, USA

Contact email: a.nowacki@leeds.ac.uk

The (proto-) Earth cooled from being in a completely molten state, to the current structure of a solid, convecting mantle overlying the liquid outer core. Since then, convection processes driving plate tectonics have homogenised the mantle. However, geochemical and geophysical data indicate that the mantle preserved pockets of unstirred material, and may even have remained molten for some time at the base of the mantle (Labrosse et al., 2007). This is an attractive idea because geochemical observations imply that part of the mantle must be capable of storing some ‘primordial’ material which is only occasionally brought to the surface and has otherwise remained ‘hidden’ for billions of years (Hofmann, 1997). Finding the source of the hidden material is perhaps the largest unsolved problem in deep Earth science: this PhD project will use novel seismic imaging techniques and simulations to detect and analyse candidate mantle structures.

Global seismic tomography has revealed that two continent-scale regions at the base of the mantle—known as the ‘Large Low-Shear Velocity Provinces’ (LLSVPs; Figure 1)—have anomalously low velocities (Garnero & McNamara, 2008), which could be caused by their being hotter than and/or chemically different to the rest of the lowermost mantle. The LLSVPs have been discussed as excellent candidates to be these ‘hidden reservoirs’ of primordial material, provided they do not dynamically interact with the rest of the mantle. A key indicator of their being distinct from the mantle would be the presence of chemically-induced strong changes in seismic velocity at their edges; however tomography is insensitive to this because of the inherent smoothing in the models it produces.

This project will use seismic observations to test if the LLSVPs could be stable, chemically-distinct features by examining waves which traverse the lowermost mantle for signs of ‘multipathing’ (Figure 2). This occurs when the velocity V varies strongly enough over a sufficiently short distance x (dV/dx ~ O(1) m/s/km), typically leading to multiple wave arrivals (when only one is expected in a smoothly-varying medium) which arrive at a different incidence angle or azimuth than usual (e.g., Ni et al., 2002). Such arrivals are excellent probes of the location, boundaries and nature of structures in the deep Earth because the presence of strong velocity gradients strongly suggests that chemical variations are the cause, which indicates that LLSVPs may be separate from convection processes.

The student will make observations of the horizontal and vertical incidence angles of multipathed arrivals of seismic phases sensitive to velocity gradients in the mantle (such as Sdiff, Pdiff, SKS and SKKS) within, around and away from the LLSVPs, using dedicated seismic arrays (e.g., the Yellowknife, Canada and Warramunga, Australia arrays) and collections of broadband seismic stations which can be grouped together for this purpose (e.g., USArray, Hi-net, F-net). By mapping the presence (and absence) of multipathing, we can create the first direct global picture of velocity gradients in the lowermost mantle, which can be compared to tomography and previous studies. Advanced 3D modelling of waveform features will be used to quantify the shape and sharpness of these features, and determine better than before whether the LLSVPs could be as ancient as is suspected.

44

Figure 1: (a) Seismic tomography of the lowermost mantle (Ritsema et al., 2010), showing the two Large Low-Shear Velocity Provinces (LLSVPs) as regions of low shear wave velocity (dVS). (b) Horizontal gradient (dVS/dx)

in velocity derived from (a). These values are underestimates due to smoothing in tomography, but suggest that strong gradients may exist near the LLSVPs.

Objectives

In this project, you will investigate the poorly-understood lowermost mantle using the study of seismic waveforms and array processing to determine how strongly heterogeneous the region is. Depending on your interests and strengths, you may choose to focus in a number of areas to develop the work and make a novel contribution to the study of the deep Earth.

1. Gather high-quality seismic datasets using seismic arrays and global broadband seismic networks, develop techniques to detect multipathing and measure discrepancies in incoming slowness and backazimuth between the data and 1D models (Rost & Thomas, 2009).

2. Examine correlations between your map of regions of strong velocity gradients and global tomography, small-scale scattering studies (Rost & Earle, 2010), core–mantle boundary topography, and other observables.

3. Use 3D, finite-frequency modelling to accurately determine the possible structures which are responsible for the seismic observations (e.g., Nowacki et al., 2016, and references therein).

4. Apply, develop and extend an automated method to detect multipathed waves using stacks of vespagrams and cluster analysis to identify true seismic arrivals.

5. Build a suite of models and the corresponding synthetic seismograms of the lowermost mantle against which seismic data can be compared automatically, again to seek out regions of high velocity gradients

45

Figure 2: Example of multipathing. (a) Path of Sdiff waves recorded at the Kaapvaal array (green triangles) from an event in Fiji (orange circle), traversing the edge of the African LLSVP. (b) Seismic data showing

multipathing Sdiff arrivals when sorted by the azimuth from the event to the station. (c) Frequency-wavenumber stack, with dark colours indicating strongest power, showing that energy arrives at the array with

deviations in backazimuth and slowness compared to the theoretical arrival (black cross, labelled) for a 1D Earth model.

Potential for high impact outcome

This work is placed to push forward our understanding of the dynamics of the whole Earth system: determining the nature of the LLSVPs is a fundamental outstanding question for all of deep Earth science. In addressing these questions you will be producing the highest-quality observations, models and hypotheses that will be published in the highest-impact journals.

Training

The student will work under the supervision of Dr Andy Nowacki and Dr Sebastian Rost, within the Institute of Geophysics and Tectonics in the School of Earth and Environment, and with Dr Mike Thorne at the Department of Geology and Geophysics, University of Utah. You will be an integral member of the Deep Earth research group in Leeds—one of the largest and most prestigious groups in the world examining how the Earth’s mantle and core behave—and have the opportunity to work with and learn from fellow researchers, both senior academics and fellow students, in a broad swathe of geophysics. You will also have the chance to visit Utah during your PhD.

You will have the chance to develop expertise in analysing data and scientific programming, including using the largest supercomputers in the country, alongside developing the core transferable skills of project management, team-working and communication. Opportunities to travel to international conferences will be part of the studentship alongside time spent in Utah. You will have access to the broad spectrum of training courses provided by the Faculty that include an extensive range of workshops from numerical modelling, managing your degree, through to preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/).

Student profile

A good applicant should have a strong background in physics or quantitative Earth science and a passion for studying how the Earth works. Interest and experience in seismology would be useful, as would some experience of programming, but not essential.

46

References

Garnero, E.J., McNamara, A.K., 2008. Structure and dynamics of Earth’s lower mantle. Science 320, 626–628. doi:10.1126/science.1148028

Hofmann, A., 1997. Mantle geochemistry: the message from oceanic volcanism. Nature 385, 219–229. doi:10.1038/385219a0

Labrosse, S., Hernlund, J., Coltice, N., 2007. A crystallizing dense magma ocean at the base of the Earth’s mantle. Nature 450, 866–869. doi:10.1038/nature06355

Ni, S., Tan, E., Gurnis, M., Helmberger, D., 2002. Sharp sides to the African superplume. Science 296, 1850–1852. doi:10.1126/science.1070698

Nowacki, A., Wookey, J., 2016. The limits of ray theory when measuring shear wave splitting in the lowermost mantle with ScS waves. Geophys J Int In press. doi:10.1093/gji/ggw358

Rost, S., Earle, P., 2010. Identifying regions of strong scattering at the core-mantle boundary from analysis of PKKP precursor energy. Earth Planet Sci Lett 297, 616–626. doi:10.1016/j.epsl.2010.07.014

Rost, S., Thomas, C., 2009. Improving seismic resolution through array processing techniques. Surv Geophys 30, 271–299. doi:10.1007/s10712-009-9070-6

47

Magmatic mass transfer through deep crust

Supervisors: Sandra Piazolo1, Dr Thomas Mueller1 , Associate Professor Nathan Daczko2

1School of Earth and Environment, University of Leeds 2 ARC Centre of Excellence CCFS, Macquarie University, Sydney, Australia)

Project partners: ARC Centre of Excellence “Core To Crust Fluid Systems”, Department of Earth and Planetary Sciences, Macquarie University, Australia (Potential CASE)

Contact email: sandra.piazolo@mq.edu.au, sandra.piazolo@leeds.ac.uk

This exciting project aims to shed light on the long standing problem of how melt is transferred through the crust by a combination of field studies in New Zealand and the European Alps, lab-based microstructural and geochemical analyses. Depending on student’s interests investigations will be augmented by a choice of high temperature or analogue experiments and/or numerical modelling.

Fluids are instrumental in the evolution of Earth’s crust and mantle; they facilitate chemical exchanges that change basic rock properties and are important for crustal differentiation at the large scale. Fluid advection of heat and mass is central to nuclear waste storage, CO2 sequestration, geothermal systems, and the formation of ore deposits. The motivation for examining transfer of melt is rooted in a fundamental gap in our knowledge. It is poorly understood how magmatic mass transfer occurs through deep crust. This project builds on observations that significant migration of melt and mass transfer at the kilometre-scale can occur in localized areas resulting in significant changes to both the melt and the host through which melt migrates (Daczko, Piazolo et al. 2016) (Fig. 1).

This project aims to achieve a new level of understanding and quantification of the underlying principles governing magmatic mass transfer through deep crust. Three main questions will be addressed:

1. Processes: What physiochemical processes are involved in magmatic mass transfer through deep crust?

2. Recognition: How can geologists recognize prior magmatic mass transfer in natural rocks? What is the physical and chemical fingerprint at micro- to meso-scales?

3. Effect: How does magmatic mass transfer affect the chemistry, geochronology, melt fertility and rheology (strength) of the crust it transfers through as well as the crust it forms at higher levels?

Figure 1. Field example of melt transfer zone in the lower crust, Fiordland, New Zealand. It shows a gabbroic gneiss (light grey) which has changed due to fluxing of a hydrous melt to an ultrabasic granofels rock

(hornblendite, dark) in a channel of melt-rock interaction (~40m wide). The melt channel is inferred to be a zone of significant mass transfer on the basis of the change in rock chemistry and mineral assemblage. For

scale see geologists in the foreground (modified after Daczko, Piazolo et al. 2016).

48

Objectives

In this project, you will work with leading scientists at Leeds, UK, and the Centre of Excellence, (Macquarie University, Australia), together with experts on the geology of the field areas to develop an in-depth understanding of how melt moves through the crust and how such melt flux influences the chemical make-up of both the transgressing melt and the material that the melt passes through. Special emphasis will be given to the feedback between deformation and melt migration. The studentship will involve

1. Field work in remote areas of Fiordland, South Island, New Zealand, and the Ivrea-Verbano zone, south part of the European Alps, northern Italy (Fig. 2).

2. In-depth analysis of samples from the two field areas. This will include chemical analysis including major and minor elements, bulk rock geochemical analysis, quantitative microstructural analysis (e.g. Smith et al. 2015) and high resolution trace element analysis using synchrotron analysis (Fig. 3).

Figure 2 Field relationships of melt related structures. (A) Melt flux zone in a high strain zone in the lower crust of Fiordland, New Zealand. (B) Melt rock interaction at Finero, Italy; note the reaction between clinopyroxene rich layers (cpx) and gabbro (former “melt”) where a hornblende-garnet- rich rim (hrbl) is formed.

In order to develop an in-depth understanding of the processes involved, the student will be able to utilize additional tools, the choice made depending on the student’s individual background and interests:

1. Numerical modelling of reactive flow

2. High temperature- high pressure experiments

3. Analogue modelling with real-time analysis (see for example Bons et al. 2001, 2008)

4. Trace element analysis using laser ablation and synchrotron techniques (e.g. Stuart et al. 2016, Fig. 3)

Potential for high impact outcome

Geochemical signatures in upper crustal magmatic and volcanic rocks suggest that they are sourced from lower crustal or even mantle environments (e.g. Bourdon et al. 2002; Gray and Kemp 2009; Vigneresse 2006). However, we do not fully understand the mechanisms responsible for magmatic mass transfer through the lower and middle crust; these are widely debated [Brown, 2004; Petford, 1996; Weinberg, 1996] and the recognition of these processes in the rock record is poor. We are in a unique position at Leeds in collaboration with the Australian Research Council Centre of Excellence “Core to Crust Fluid Systems” (CCFS, http://www.ccfs.mq.edu.au/, Macquarie University,Australia) to answer important unresolved questions about how magma moves through the crust. This knowledge is fundamental to our understanding of Earths’ evolution. At the same time, the understanding of reactive flow and tools to recognize, predict and model reactive flow is

49

fundamental to many problems facing society (e.g. CO2 sequestration, security of nuclear waste deposits, ore mineral formation). Hence, beside the advances in the fundamental understanding of crustal formation and evolution, the tools developed throughout this project have immediate policy-relevant implications. Consequently, we anticipate the project generating several papers being suitable for submission to high impact journals.

Figure 3: Example of the application of trace element analysis to melt flux related processes utilizing high end synchrotron analysis (modified after Stuart et al. 2016). (a) Overview photomicrograph of a gabbroic gneiss in plain polarized light showing pyroxenes with incipient coronas of hornblende and quartz intergrowths representing replacement microstructures. FOV = 18 mm. (c) Sr concentration in plagioclase derived by synchrotron based analysis (black low, white high concentrations) of same area as shown in (a); pyroxenes are marked in black. Note that Sr is enriched next to the replacement microstructures and in bands connecting individual coronas across samples. (e) Possible interpretation: Schematic diagram illustrating the interpreted flow of melt as highlighted by the high Sr concentrations; grey areas are plagioclase rich domains. Melt is interpreted to have moved along pyroxene/corona boundaries parallel to foliation (red), accumulated and reacted in embayments (green), and moved along plagioclase-plagioclase boundaries forming ‘bridges’ (blue).

Training & Framework of the project

The student will work under the supervision of Assoc. Prof Sandra Piazolo and Dr Thomas Mueller within the IGT metamorphic and structural geology group. This project provides a high level of specialist scientific training in: (i) Field work and targeted sampling in lower crustal sections, (ii) state-of-the-art analytical techniques with special emphasis on both chemical and structural analysis of geomaterials; along with a selection of other skills including numerical modelling of reactive flow, high temperature and pressure experiments and analogue modelling. Co-supervision will involve regular meetings between partners and extended visits for the student to the Centre of Excellence “Core to Crust Fluid Systems” (CCFS, Macquarie University, Australia), where the student will work under the supervision of Assoc. Prof Nathan Daczko.

The successful PhD student will have access to a broad spectrum of training workshops put on by the Faculty that include an extensive range of training workshops in numerical modelling, managing your degree, and preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). The student will not only benefit from the experts and facilities at Leeds University but also the ARC Centre of Excellence “Core to Crust Fluid Systems” located at Macquarie University.

50

The student will be part of a larger joint research effort currently under way both at Leeds University and CCFS (Macquarie University) involving at least 3 PhD students with collaborators within the School at Leeds and partners in Sydney and Padua. As such, the student will be part of an active group excited to unravel the processes and signatures involved in reactive fluid flow and mass transfer.

Student profile

The student should have a strong interest in structural geology/ metamorphic geology / igneous petrology and their combination, love for field work and thinking out of the box. A background (advanced high school level or undergraduate courses) in a quantitative science (maths, physics, chemistry) will be of advantage. Willingness to work within a research team is essential. A Masters of Research or similar in a relevant area will increase the chances to get a scholarship.

CASE Partner

The proposal has been agreed as a “Partnership Project” (a potential CASE project) with CCFS, Macquarie University providing extra funding additional to the NERC student stipend.

References

• Bons, P. D., Elburg, M. A. and Dougherty-Page, J. (2001). Analogue modelling of segregation and ascent of magma. In: Ailleres, L. and Rawling, T. 2001. Animations in Geology. Journal of the Virtual Explorer, 4.

• Bons, Paul D., et al. (2008) Finding what is now not there anymore: Recognizing missing fluid and magma volumes. Geology 36, 851-854.

• Bourdon, E., J.-P. Eissen, M. Monzier, C. Robin, H. Martin, J. Cotten, and M. L. Hall (2002), Adakite-like lavas from Antisana Volcano (Ecuador): Evidence for slab melt metasomatism beneath Andean Northern Volcanic Zone, Journal of Petrology, 43(2), 199-217.

• Brown, M. (2004), The mechanism of melt extraction from lower continental crust of orogens, Geological Society of America Special Papers, 389, 35-48.

• Daczko, N.R., Piazolo, S., Meek, U., Stuart, C.A. and Elliott, V. (2016), Hornblendite delineates zones of mass transfer through the lower crust, Scientific Reports, 6, 31369, doi:10.1038/srep31369.

• Gray, C. M., and A. I. S. Kemp (2009), The two-component model for the genesis of granitic rocks in southeastern Australia — Nature of the metasedimentary-derived and basaltic end members, Lithos, 111(3–4), 113-124.

• Klepeis, K. A., Schwartz, J., Stowell, H., & Tulloch, A. (2016), Gneiss domes, vertical and horizontal mass transfer, and the initiation of extension in the hot lower-crustal root of a continental arc, Fiordland, New Zealand, Lithosphere, 8(2), 116-140.

• Petford, N. (1996), Dykes or diapirs?, Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 87(1-2), 105-114.

• Stuart, C.A., Piazolo, S. and Daczko, N.R. (2016), Mass transfer in the lower crust: evidence for incipient melt assisted flow along grain boundaries in the deep arc granultes of Fiordland, New Zealand, Geochemistry, Geophysics, Geosystems (G3), doi: 10.1002/2015GC006236.

• Smith, J. R., Piazolo, S., Daczko, N. R., & Evans, L. (2015). The effect of pre‐tectonic reaction and annealing extent on behaviour during subsequent deformation: insights from paired shear zones in the lower crust of Fiordland, New Zealand. Journal of Metamorphic Geology, 33(6), 557-577.

51

• Vigneresse, J. L. (2006), Granitic batholiths: from pervasive and continuous melting in the lower crust to discontinuous and spaced plutonism in the upper crust, Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 97(04), 311-324.

• Weinberg, R. F. (1996), Ascent mechanism of felsic magmas: news and views, Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 87(1-2), 95-103.

52

Towards an understanding of Earth's structure - The development of

adaptive optics approaches for Seismology

Supervisors: Dr Sebastian Rost1, Dr Neil Selby2and Dr Andy Nowacki1

1School of Earth and Environment, University of Leeds 2 AWE Blacknest

Project partner: AWE Blacknest (CASE)

Contact email: s.rost@leeds.ac.uk

The Earth is heterogeneous on many scale-lengths - Pick up a crustal rock and you see the

heterogeneity on a grain scale, look at a geological map to see the heterogeneity of Earth’s crust and

look at the differences between oceans and continents to see evidence for the heterogeneity on a

global scale. This heterogeneity we see at the surface of the Earth can also be found in the interior of

our planet and is the expression of the dynamics and evolution of our planet. Imaging this expected

heterogeneity in the Earth’s interior is one of the grand challenges of Seismology.

Over the last few decades our understanding of the large-scale structure of the Earth’s interior, as

imaged e.g. with seismic tomography, has started to converge and our understanding of the

dynamics and origin of many features in the models has improved. On the other hand, the small-

scale structure (i.e. smaller than a few hundred kilometres) of Earth’s interior remains controversial

and ill-resolved. This is partly due to the limitations of seismology to resolve small-scale structure

due to the seismic wavelength. To understand the structure, evolution and dynamics of our planet

we require knowledge and understanding of structures across the full spectrum of heterogeneities

found in the Earth. This project aims to improve our understanding of the fine-scale structure of

the Earth and will contribute to a better understanding of Earth’s dynamics.

Earthquake seismology is one of the main remote sensing tools for the interior structure of the

Earth. Using information extracted from the seismic wavefield we are able to understand both the

source mechanisms and the structure along the propagation path. E.g. the large-scale structure

along the path can be resolved using seismic tomography and smaller scale structure and

information on the source mechanism can be resolved using waveform information. This project will

focus on extracting information on the Earth’s fine scale structure from the seismic wavefield by

using scattered seismic energy. The scattered wavefield contains structural information on the km

scale and allows insight into many processes at Earth’s surface and in its interior (Revenaugh, 1999).

Elastic waves scatter at heterogeneities with scale lengths on the same order as the seismic

wavefield and many sections of recorded seismograms are dominated by scattered energy (Rost et

al., 2015; Shearer, 2007; Shearer and Earle, 2008).

53

Figure 1: (top) Typical scale lengths

of Earth heterogeneity and seismic

probe to image the heterogeneity.

The largest scales are resolvable

using traveltime tomography with

shorter scales being imaged using

waveform inversions. The shortest

resolvable scales manifest in the

scattered seismic wavefield and will

be used here. After Rost et al.,

(2015). (Bottom) Geodynamic

simulation of Earth structure

showing the different scale

structures (e.g. LLSVPs, subduction,

plumes and crustal remnants)

imaged using these probes. After

(Van Keken et al., 2002)

The strongest seismic heterogeneities can typically be found in the Earth’s lithosphere (Korn, 1988,

1990). Since most seismic stations are located at the Earth’s surface (Figure 2), these heterogeneities

restrict our ability to image and understand Earth structure and source mechanisms further along

the seismic raypath. This project aims to develop a methodology similar to adaptive optics to

remove the effects of the shallow heterogeneities on the seismic waveform to improve imaging of

path structure and source mechanism.

Adaptive optics is a technology used to improve the performance of optical systems by reducing the

effect of wavefront distortions from atmospheric conditions and is commonly used with

astronomical telescopes. For seismology we will characterize the structure beneath a station using a

large database of seismic recordings and will use wavefront simulation techniques to predict the

influence of the structure on the waveform. The project will then develop methodology to remove

this influence from the incoming wave field, which will allow us to image structure along the path

and the source mechanism better. Similar approaches have recently been adopted in hydrocarbon

reservoir imaging (Etgen et al., 2014).

54

Figure 2: Schematics of the effect of scattering media of different thicknesses, scattering attenuation (Qs), and

anelastic attenuation (Qa) on a wavefront in terms of time (shape of wavefront) and amplitude (shading of

wavefront) for scenarios with (a) shallow scattering only and (b) shallow and deep scattering. In this case, the

effect of the known shallow structure on the wavefront (determined using shallowly penetrating waves) can be

taken into account to determine the effect of the deep structure along (image courtesy of D. Frost (UC

Berkeley)).

Objectives

The project can be divided in three parts that will roughly map onto the three years of the

candidature.

Part 1 will characterize the small-scale heterogeneities beneath the primary arrays of the

Comprehensive Test Ban Treaty (CTBT) Organization (https://www.ctbto.org) to monitor

underground nuclear explosions. These arrays are used to monitor underground nuclear explosions.

AWE Blacknest, the CASE partner, is the UK National Data Centre for the CTBT, and one of its roles is

to develop enhanced methods for the monitoring of the Treaty. The information on small-scale

structure beneath the arrays will be important for CTBTO scientists for better monitoring of

explosions globally. The CTBTO arrays are ideal for method development since they cover a wide

range of tectonic regions, are typically installed in seismically quiet regions, have large data

catalogues and allow 3D analysis of the incident seismic wavefield (Dainty and Toksoz, 1990).

The second part of the project will develop a methodology to remove the near-receiver structure

from the seismic wavefield – the adaptive optics process. This will include synthetic modelling of the

seismic wavefield in 3D media and theoretical development of the seismic adaptive optics.

The final part will test the feasibility to apply these methods to installation of seismometer e.g. as

part of USArray (http://www.earthscope.org) or using dense deployments in Europe. Using stations

deployed over a wide range of tectonic terranes will not only allow characterization of the

lithosphere in these regions but will also allow tests how widely the adaptive optics approach is

applicable to other seismic imaging techniques.

The work will be presented at international conferences such as the annual meeting of the American

Geophysical Union (San Francisco/New Orleans), the European Geosciences Union (Vienna) or the

Science and Technology Conference Series of the CTBTO (Vienna). Extended visits to CTBTO (Vienna)

or national institutions for explosion monitoring (e.g. NORSAR in Norway or the US Geological

Survey) are also possible.

55

Training

This project is suited for students with a background in geophysics, natural sciences, geosciences,

physics or mathematics with a strong interest in seismic data analysis, Earth structure and dynamics.

The successful candidate will develop a deep understanding of seismic wave propagation through

the analysis of seismic data and synthetic modelling of seismic wave propagation in heterogeneous

media. The project will entail several placements at AWE Blacknest allowing interaction with experts

in source localisation and characterization. The skills obtained in this project are transferrable to a

variety of fields including the hydrocarbon industry and global earthquake seismology. All three

objectives will lead to high quality publications and the methods developed in this project aim to be

applied within the CTBTO.

Potential for high impact outcome

The project will represent a significant contribution to our understanding of the effects of Earth

structure on the seismic wavefield. The adaptive optics approach will allow us to account for several

imaging errors and will sharpen our images of Earth structure elsewhere along the seismic raypath.

The work will be easily divisible into peer-reviewed publications that will form consecutive chapters

of a PhD thesis as described under Objectives.

Research Environment

The applicant will be located in the Institute of Geophysics and Tectonics

(http://www.see.leeds.ac.uk/research/igt/) at the contact point between the Deep Earth Research

Group (http://www.see.leeds.ac.uk/research/igt/deep-earth-research/) and the research group for

Geodynamics & Tectonics (http://www.see.leeds.ac.uk/research/igt/geodynamics-and-tectonics-

group/).

The Deep Earth Research Group is one of the world’s largest groups of scientists studying the

structure and dynamics of Earth’s core and mantle. Research topics include the dynamics and

structure of the Earth’s magnetic field and convection in the outer core, material properties under

high pressure and temperature and Global Seismology. The Group collaborates closely with the

Department of Applied Mathematics in Leeds and Deep Earth research groups worldwide.

The Geodynamics & Tectonics group aims to understand the processes that form and change the

surface of the Earth through remote sensing, seismology, structural geology and geodynamics.

The Institute of Geophysics and Tectonics comprises several research group including Geodynamics

& Tectonics, Volcanology, High Temperature Geochemistry as well as Deep Earth Research. Several

of the research groups use seismology as a research tool and the institute offers a diverse and

supportive research environment.

CASE Partner

This project is a potential CASE project in collaboration with AWE Blacknest and one of the

supervisors will be located there. Successful applicants will spend time at AWE Blacknest during

several placements. Blacknest’s roles include seismic monitoring of adherence to the Comprehensive

Test Ban Treaty (CTBT) designed to prevent nuclear explosions, such as the recent nuclear tests in

North Korea. AWE Blacknest will provide additional funding for research and travel expenses and will

provide access to the data of the CTBTO.

56

References and further reading

• Dainty, A., Toksoz, M., 1990. Array analysis of seismic scattering. Bull. Seismol. Soc. Am. 80,

2242–2260.

• Etgen, J.T., Ahmed, I., Zhou, M., 2014. Seismic Adaptive Optics. Presented at the 2014 SEG

Annual Meeting, Society of Exploration Geophysicists.

• Korn, M., 1990. A modified energy flux model for lithospheric scattering of teleseismic body

waves. Geophys. J. Int. 102, 165–175. doi:10.1111/j.1365-246X.1990.tb00538.x

• Korn, M., 1988. P-Wave Coda Analysis of Short-Period Array Data and the Scattering and

Absorptive Properties of the Lithosphere. Geophys. J.-Oxf. 93, 437–449. doi:10.1111/j.1365-

246X.1988.tb03871.x

• Revenaugh, J., 1999. Geologic applications of seismic scattering. Annu. Rev. Earth Planet. Sci.

27, 55–73.

• Rost, S., Earle, P.S., Shearer, P.M., Frost, D.A., Selby, N.D., 2015. Seismic Detections of small-

scale heterogeneities in the deep Earth, in: The Earth’s Heterogeneous Mantle, Springer

Geophysics. Springer, pp. 367–390.

• Shearer, P.M., 2007. Deep Earth Structure - Seismic Scattering in the Deep Earth, in: Treatise

on Geophysics. Elsevier, Amsterdam, pp. 695–729.

• Shearer, P.M., Earle, P.S., 2008. Chapter 6 Observing and Modeling Elastic Scattering in the

Deep Earth, in: Earth Heterogeneity and Scattering Effects on Seismic Waves. Elsevier, pp.

167–193.

• Van Keken, P.E., Hauri, E.H., Ballentine, C.J., 2002. Mantle Mixing: The Generation,

Preservation, and Destruction of Chemical Heterogeneity. Annu. Rev. Earth Planet. Sci. 30,

493–525. doi:10.1146/annurev.earth.30.091201.141236

57

Petrological & geochemical insights into subduction initiation- the case of Izu-

Bonin-Mariana volcanic arc

Supervisors: Dr Ivan Savov and Dr Jason Harvey

Project partners: Professor Rosemary Hickey-Vargas (FIU) and Gene Yogodzhinski (USC)

Contact email: i.savov@see.leeds.ac.uk

Convergent margins mark sites of plate destruction and are unique to Earth among the terrestrial

planets. However, currently we lack clear understanding of why and how they are initiated. Among a

number of hypotheses that have been proposed, the so-called “spontaneous subduction initiation”

model appears particularly relevant (Stern, 2004; Arculus et al, 2015) to the initiation of one of the

largest, nominally intra-oceanic subduction zones in the W. Pacific-the Izu-Bonin-Mariana (IBM)

system. Spontaneous subduction initiation occurs when a change in plate motion allows the

gravitationally unstable lithosphere to founder along an existing plate boundary. The IBM system

(Fig. 1A) represents an example of arc initiation wherein subsidence of relatively old Pacific

lithosphere began along a system of transform faults/fracture zones adjacent to relatively buoyant

lithosphere. The initial record on the overriding plate during the spontaneous subduction

commences with rifting, spreading, and formation of magmas such as highly depleted, low-K

tholeiites and boninites (Hickey-Vargas et al., 2007; Ishizuka et al., 2011; Arculus et al., 2015).

Figure 1A (left): Regional geology of the IBM arc-basin system south of Japan. Currently active volcanic arc

front (thick green solid line), back arc basin rifts (thick black solid lines) and remnant (early) arcs (thick green

stippled lines) are shown. Filled circles are ODP drill sites, and crosses are DSDP drill sites. The sites from which

fallout tephra is recovered are highlighted in blue. Also shown is the location of the IBM-1 cite (red circle; this

proposal). Figure 1B(right): 143Nd/144Nd trends for the IBM volcanics. The trend towards higher 143Nd/144Nd

at the Izu Bonin VF (and maybe in the Mariana VF) is interpreted as reflecting variations of the mantle

fertilization due to changes in the slab/sediment fluxes over time [Straub et al., 2004, 2009]. Note that for both

58

arcs the early (Paleogene) records are almost unknown, although the limited samples available (Site 1201;

Savov et al., 2006-see green and blue fields) show truly fascinating insights into the temporal evolution of the

subarc mantle feeding arc volcanism. Data sources after Schmidt [2001]; Straub [2003, 2004]; Savov et al.,

[2006].

Following subduction initiation, further igneous development is fundamental to the creation of arc

volcanic chains, which in turn is essential to the formation and evolution of continental crust. Testing

models of subduction initiation and subsequent arc evolution requires identification and exploration

of regions adjacent to an arc, where pre-arc crust (basement) is directly overlain by undisturbed arc-

derived materials. The IBM system is globally important because we have clear evidence for the age

(~52 Ma; Ishizuka et al., 2011) and exact site of inception, (Kyushu-Palau Ridge; Fig 1A), the duration

of arc activity, and changes in magmatic composition and volumes through time through extensive

drilling (ash & pyroclast records) and dredging (Fig. 1A).

Dr I. Savov sailed as shipboard scientist on IODP Exp. 351, which successfully drilled site IBM-1 at the

Amami Sankaku Basin (ASB), just west of the KPR proto-arc (Fig. 1A). The site penetrated the pre-arc

IBM basement (Early Eocene) and the overlying 1400m of volcaniclastic sediments. Studying the

sedimentary cover is crucial to decipher the geochemical and petrological evolution of the post-arc

inception volcanism in the entire IBM region. The primary target of this PhD studentship is to sample

and subsequently study the arc- derived sediments directly overlaying the basement at site IBM-1. In

analogy to the previously drilled site 1201 (where Dr. Savov also sailed as shipboard scientists and

studied extensively- see Savov et al., 2006; Hickey-Vargas et al., 2007), these sediments should

preserve the explosive ash and pyroclastic fragmental records for at least the first 25 M.yrs. of the

developing nearby volcanic arc (KPR). To date, the geochemical data available for such materials

recovered from the fore-arc regions of the IBM system (site 782, see also Fig. 1A) are concentrated

in the Neogene (e.g., Straub, 2003, 2004) and only limited Paleogene record of volcaniclastics and

ash material that is well-dated AND appropriate for geochemical study is available from any of the

existing DSDP/ODP Sites (incl. 291, 292, 294, 446-447 & 1201; Savov et al., 2006; Hickey-Vargas et

al., 2007; Ishizuka et al., 2011; see Fig. 1A&B). Increasing the resolution of the post-IBM arc inception

records will allow geochemical modelling aiding the quantification of the volumes of sediment, crust

and mantle involved in the early arc volcanism.

In detail, the PhD student will construct geochemical profiles across the entire Cenozoic, with

emphasis on the Paleogene volcaniclastics. The student will analyse the volcanic ash and the most

unaltered volcaniclasts for Sr, Nd, Pb and B isotopes in the TIMS Lab at the Univ. Leeds. These

isotope systems, in addition to major and trace element variations, have been shown to be a

powerful tool for resolving provenance (Pb, Sr), as well as uniquely trace the sedimentary and/or

crustal (slab) and mantle contributions (Sr, B and Nd) to arcs (Straub, 2004; Hickey-Vargas et al,

2007; see also Fig. 1B). Using a combination of elemental and isotope tracers will allow the PhD

student to uniquely quantify the volumes of fluids/melts involved in the sources of the earliest

volcanic eruptions that took place at the IBM (see Savov et al., 2006 and Hickey-Vargas et al., 2007).

This task is critical for the subduction initiation modelling and also for better understanding of the

causes of the modern along-IBM major element and isotope variations (Stern, 2004; Ishizuka et al.,

2011). After vigorous examination under polarized microscope and with the help of the state-of-the-

art SEM and EPMA Facility at Univ. Leeds, the student will be able to identify up to 20 unaltered

volcaniclasts and ash samples that are appropriate for Ar-Ar dating. In collaboration with the co-

chief scientist O. Ishizuka (Ar-Ar Lab at AIST, Japan) splits of these same samples will be dated. This,

59

in addition to the ages derived from the nanofossil record (shipboard data), will allow the student to

constrain very precisely the temporal intervals that the selected IBM-1 sediments represent. Once

this is known, the student will connect the anticipated results with the existing (mostly Neogene)

ash and volcaniclasts datasets from other parts of the IBM (see Fig 1B; Bryant et al., 1999; Straub,

2003; Straub et al., 2004) and other W. Pacific sites (Savov et al., 2006; Hickey-Vargas et al., 2007,

Ishizuka et al., 2011). Together, the combined age and isotope results are expected to be a major

step toward the more complete understanding of the temporal chemical and petrological evolution

of the arc volcanism after subduction initiation, which is an issue remaining largely unknown.

Desirable (but not required) background

Students with experience in the field of geochemistry and/or petrology are encouraged to apply.

Potential for high impact outcome

A recently published Nature Geoscience paper involving Dr. Savov (see Arculus et al., 2015) reported

only the limited shipboard major and minor element geochemical data from Exp. 351. Building an

insights from 3 additional radiogenic (Sr-Nd and Pb) and one novel stable isotope system (boron)

and their power to uniquely decipher high temperature processes such as magma sources and

volumes, is an excellent sign that the contributions from this studentship will be able to deliver

publications in high impact journals . The processes of subduction zone initiation are identified as

Challenge 11 of the Science Plan of IODP (www.iodp.org/ science-plan-for-2013-2023). As IODP is an

international scientific effort and major investment (multi-million £) and since IBM has been

repeatedly selected as a major target to understand subduction processes, the proposed

studentship will surely be on the spotlight for new and unique insights derived from carefully

selected tracers, which overall will be able to contribute to publications in the field of petrology,

geochemistry and volcanology.

Training and Support

The student will join two active research groups of the Institute of Geophysics & Tectonics (IGT): the

High Temperature Geochemistry Research Group and the Volcano Studies Group (more info on

group members and current projects can be found here:

http://www.see.leeds.ac.uk/research/igt/high-temperature-geochemistry/ and here:

http://www.see.leeds.ac.uk/research/igt/high-temperature-geochemistry/). Training of in-situ

mineral chemistry via EPMA/LA-ICP-MS techniques, as well as isotope ratio determination via TIMS

instrument will be provided in- house or in the labs of our long term research partners at CNR-Pisa

(Italy) and the Ar-Ar Facility at AIST (Japan).

Selected Relevant Publications

• Arculus et al., 2015; A record of spontaneous subduction initiation in the Izu–Bonin–Mariana

arc, Nature Geoscience 8 (9), 728-733.

• Bryant et al., 1999. Laser ablation–inductively coupled plasma–mass spectrometry and

tephras: a new approach to understanding arc-magma genesis. Geology, 27(12):1119–1122.

• Hickey-Vargas et al., 2007. Origin of diverse geochemical signatures in igneous rocks from

the West Philippine Basin, AGU Geophysical Monograph Series, vol. 166, 287-303.

• Ishizuka et al., 2011. Making and breaking an island arc: a new perspective from the

Oligocene Kyushu-Palau arc, Philippine Sea. G-cubed, 12(5):Q05005.

60

• Savov et al., 2006. Petrology and geochemistry of West Philippine Basin basalts and early

Palau-Kyushu arc volcanic clasts from ODP Leg 195, Site 1201D: Implications for the early

history of the Izu- Bonin- Mariana arc, J. Petrology, 47(2): 277-299.

• Straub et al., 2004. Volcanic glasses at the Izu arc volcanic front: new perspectives on fluid

and sediment melt recycling in subduction zones. G-cubed 5(1):Q01007.

61

Anisotropy and anelasticity of HCP metals: a key to the dynamics of Earth's

inner core

Supervisors: Dr Andrew Walker, Dr Jon Mound, Dr Chris Davies and Dr Stephen Stackhouse

School of Earth and Environment, University of Leeds

Contact email: a.walker@leeds.ac.uk

The solid iron inner core is the most remote and inaccessible part of our planet but its structure and

composition may provide a key record needed to untangle the geological history of the surface

environment. Information encoded in the inner core during its solidification could reveal the timing

and nature of the onset of Earth’s protective magnetic field generated by convection in the liquid

outer core or even of changes in the way the mantle convects and drives surface dynamics. Key to

developing our understanding of the inner core is our ability to use seismic observations to constrain

its structure on all scales. Seismic wave velocities are mostly sensitive to the atomic scale crystal

structure, temperature and composition. On a larger scale the microstructure of the inner core,

reflecting its deformation and crystallization history, can be probed by seismic studies of elastic

anisotropy (variation of wave velocity with direction) and anelasticity (responsible for the time lag

between the deformation associated with the passage of seismic energy and recovery to the pre-

strained state leading observable to seismic signals). Seismic observations in principle allow us to

infer the inner core’s history of growth and deformation, but require information on the material

properties of hexagonal close packed (HCP) iron – the high-pressure phase of iron expected to form

the inner core. The overall aim of this project is to make use of atomic scale simulations to provide

this information. In particular, you will seek to understand the origin of anisotropy and analesticity in

the inner core and use this understanding to decode the information hidden in the center of the

Earth.

Figure 1: cartoon showing the dynamics of the Earth’s interior. Convection in the mantle drives plate tectonics

at the surface and cools the outer core to drive the generation of the magnetic field. Growth of the inner core

provides additional power for magnetic field generation and its crystallization leaves evidence of Earth’s history

62

at the center of the planet (such as the green ‘inner inner core’ or textured anisotropic material forming much

of the inner core in this image). From Ed Garnero (http://garnero.asu.edu/).

The deformation mode of solids is dependent on the time scale and magnitude of stress as well as

the temperature, pressure and microstructure. On the shortest time scales and well below the

melting point small stresses result in elastic strains where stored energy is immediately returned

once the stress is removed. On much longer time scales and typically at higher temperature stress

can cause the motion of imperfections in the crystal structure (such as point defects, dislocations

and grain boundaries) leading to irrecoverable plastic deformation. Between these extremes, stress

applied at seismic frequencies leads to strain by the realignment of crystal imperfections. When the

stress is removed the strain disappears after a delay time that is characteristic of the deformation

mechanism. This anelasticity leads to frequency dependent moduli and loss of energy from the

mechanical system. These processes are seismically observed in the core [1,2] and known to

seismologists as dispersion and intrinsic attenuation. They link seismology and the nature of the

imperfections within crystals that are the inevitable result of deformation or growth. Therefore,

seismic observation of dispersion and attenuation of the inner core provides key information on its

growth and dynamics. These observations are now being made, including new study of normal

modes (where large earthquakes make the planet 'ring like a bell'), but in order to interpret them

experimental data on the controls of anelasticity in core materials are needed [3,4]. However, the

most recent study of the anelasticity of iron [5] is now over a decade old and is limited to low

pressure where iron adopts the body centered cubic (BCC) or face centered cubic (FCC) structure. It

is now widely, although not universally, accepted that iron in the core adopts the HCP structure.

There are no results that reveal the anelasticity of this core-forming phase.

Advances in atomic scale simulation techniques, where the properties of Earth materials are

predicted by considering the behaviour of the electrons, and improvement in the power and

availability of high performance computing, allows the properties of materials at extreme pressure

and temperature to be predicted without recourse to experiment. These methods allow the nature

of crystal imperfections to be examined and this, in turn, allows us to study the viscosity and

anelasticity of the inner core. Use of these methods lies at the center of this project.

The project

In order to provide the information needed to understand the origin and evolution of the inner core,

you will undertake atomic scale simulations of point defects and dislocations in HCP iron. The project

will evolve in a number of distinct steps as you develop a mastery of atomic scale simulation

techniques. In particular, you will:

Simulate the structure, mobility and vibrational properties of point defects (atomic

impurities) in order to test and quantify the idea that the motion of point defects is

responsible for attenuation in the inner core [4].

Study the nature of dislocations (line defects) [6] in HCP iron, to provide constraints on the

viscosity of the core, explore the mechanism leading to anisotropy, and probe the possibility

of dislocation damping as the origin of anelasticity.

Construct combined models of the viscosity and anelasticity of HCP iron under the

conditions found in the core, and link these to models of inner core growth and

deformation.

63

With these results in hand, you will examine the possibility of deformation of the growing inner core

as the origin of seismic anisotropy and how the anelastic and anisotropic structure can be used to

reveal the growth history of the inner core.

Training environment

You will receive training in skills tailored to the project but also useful to help secure a future career

as a research scientist in academia or elsewhere. To allow you to complete the project you will learn

to use a wide range of atomic scale simulation methods and, in particular, the application of density

functional theory to defects in solids. You will need to master the application of lattice dynamics and

molecular dynamics, and become skilled in the analysis of the results of atomic scale simulation.

These advanced methods have great utility across a wide range of science and industry. Some

examples from beyond the Earth sciences include use in drug discovery and development, advanced

materials design and optimisation for engineering applications, and the development of green solar

and fuel cell energy technologies. You will also learn how to confidently develop software for the

analysis of results and to use large-scale high performance computing resources. Alongside the

transferable skills in communication and management this can open a wide range of career

pathways. These skills will be developed by a mixture of hands on experience, attending external

training courses, and by participating in the Leeds – York NERC doctoral training partnership

programme

Figure 2: University of Leeds hosted tier 2 high performance computing facility of the N8 HPC consortium

(http://n8.hpc.org.uk), one of the supercomputers that can be used in this project.

Student profile

You will have a good first degree in the physical sciences (e.g. physics, chemistry or geology) that

included modules in mineralogy, crystallography or other subjects including components of

condensed matter physics. The ideal candidate will also have experience of basic scientific

programming and computation possibly derived from the completion of an undergraduate research

project.

References and further reading

• [1] I. Sumita and M. I. Bergman (2007) Inner-core dynamics. Core Dynamics: Treatise on

Geophysics volume 8 (P. Olson, ed.). Elsevier, Amsterdam.

• [2] D. J. Doornbos (1974) The anelasticity of the inner core. Geophysical Journal of the Royal

Astronomical Society 38:397-415

64

• [3] A. M. Makinen and A. Deuss (2013) Normal mode splitting function measurements of

anelasticity and attenuation in Earth’s inner core. Geophysical Journal International 194:401-

416.

• [4] A. M. Makinen, A. Deussn and S. A. T. Redfern (2014) Anisotropy of Earth’s inner core

intrinsic attenuation from seismic normal mode models. Earth and Planetary Science Letters

404:354-364.

• [5] I. Jackson, J. D. Fitz Gerald and H. Kokkonen (2000) High-temperature viscoelastic

relaxation in iron and its implication for the shear modulus and attenuation of the Earth’s

inner core. Journal of Geophysical Research 105:23605-23634.

• [6] A. M. Walker, P. Carrez, and P. Cordier (2010) Atomic-scale models of dislocation cores in

minerals: progress and prospects. Mineralogical Magazine, 74:381-413.

65

The relationship between short-term tectonics and mountain building in New

Zealand

Supervisors: Professor Tim Wright1, Dr John Elliott1, Dr Sandra Piazolo1 and Dr Ian Hamling2

1School of Earth and Environment, University of Leeds 2 GNS New Zealand

Project partner: GNS New Zealand (CASE)

Contact email: t.j.wright@leeds.ac.uk

The project aims to improve our understanding of how mountains are built by combining high resolution geodetic (InSAR, GPS) measurements of present-day deformation in the South Island of New Zealand with geological data collected from the exhumed roots of the Alpine Fault.

In collisional zones, mountains are made by the interaction of external tectonic driving forces, internal gravitational forces and surface processes (erosion). The response of the crust to these forces is governed by the rheology of the crust. In the continents, one key question is whether crustal strength lies only in the upper seismogenic layer (Jackson, 2008) or is instead found in both the crust and mantle (Burov, 2010). Another key question is the degree to which mountain chains are supported dynamically by flow in the mantle (Molnar, 2013). This project will address these major questions by combining new observations from satellite geodesy (InSAR and GPS) with rheological constrained from lower-crustal rocks exhumed in the Southern Alps of New Zealand, an area of rapid continent-continent collision.

Figure 1: Vertical rates of motion across the Southern Alps in New Zealand, adapted from Beavan et al. (2010). Data are only available for a 1D profile; InSAR observations collected in this project will map vertical rates

across the entire South Island of New Zealand.

The South Island of New Zealand is being deformed rapidly by the oblique collision of continental fragments on two tectonic plates (Okaya et al., 2013). This has created the dramatic Southern Alps and the Alpine Fault. Importantly, in the context of this project, high levels of annual rainfall are leading to rapid erosion and exhumation of rocks that had been deformed in the lower crust. Measuring the present-day rates of vertical motion across the Southern Alps is key to unravelling the factors that control the formation of mountains, but existing measurements from GPS are very sparse (Beavan et al., 2010). The recent launch of the Sentinel-1 constellation provides an exciting opportunity to map vertical motions over the entire South Island for the first time (Elliott et al., 2015). By combining these observations with geological constraints on the rheology of rocks exhumed from the lower crust (Gardner et al., 2016), the student will be uniquely placed to test models of how this major mountain chain was formed, and in particular to assess the contribution of strength in the lower crust and dynamic uplift from flow in the mantle.

66

Objectives

The project will have the following specific objectives:

1. The student will use data from the new Sentinel-1 radar constellation to measure present-day rates of “line-of-sight” motion using InSAR in the South Island of New Zealand.

2. In collaboration with CASE partner GNS New Zealand, who are responsible for GPS monitoring of deformation in New Zealand, and COMET partners in the UK, the student will combine the InSAR and GPS observations (e.g. Walters et al., 2014) to estimate a high-resolution 3D velocity field for the South Island of New Zealand. This will be the first time that vertical motions have been mapped across the entire mountain range.

3. The student will analyse the microstructures and fabrics recorded in geological samples collected from the Southern Alps to place constraints on the rheology of the lower crust during the period of deformation.

4. The data from the first three components will be used to test simple models of continental collision, assess the strength of the lower crust, and determine the contribution of dynamic topography to the formation of the Southern Alps.

We would expect the balance between these components to vary depending on the specific interests of the student.

Additional Information

The project is a CASE studentship with partner GNS New Zealand. As such the student will spend 3 months working with co-supervisor Dr Ian Hamling in Lower Hutt (Wellington). ). During the visit, it will be possible for the student to take part in a field trip to the Alpine Fault Zone on the South Island to collect sample for subsequent in-depth analysis. The student will have access to the excellent state-of-art analytical equipment available at Leeds. The student will be a member of COMET, the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics, and will be encouraged to collaborate with COMET partners across the UK.

The project would suit a numerate student with a background in earth sciences, geology, geophysics, physics or similar subjects. They will be provided with training in state of the art geodetic methods, computational techniques, and microstructural analysis.

References/Further Reading

• BEAVAN, J., DENYS, P., DENHAM, M., HAGER, B., HERRING, T. & MOLNAR, P. 2010. Distribution of present‐day vertical deformation across the Southern Alps, New Zealand, from 10 years of GPS data. Geophysical Research Letters, 37.

• BUROV, E. 2010. The equivalent elastic thickness (Te), seismicity and the long-term rheology of continental lithosphere: Time to burn-out “crème brûlée”?: Insights from large-scale geodynamic modeling. Tectonophysics, 484, 4-26.

• ELLIOTT, J., ELLIOTT, A., HOOPER, A., LARSEN, Y., MARINKOVIC, P. & WRIGHT, T. 2015. Earthquake monitoring gets boost from new satellite. Eos, 96.

• GARDNER, R. L., PIAZOLO, S. & DACZKO, N. R. 2016. Shape of pinch and swell structures as a viscosity indicator: Application to lower crustal polyphase rocks. Journal of Structural Geology, 88, 32-45.

• JACKSON, J., MCKENZIE, D., PRIESTLEY, K. & EMMERSON, B. 2008. New views on the structure and rheology of the lithosphere. Journal of the Geological Society, 165, 453-465.

67

• MOLNAR, P. & HOUSEMAN, G. A. 2013. Rayleigh‐Taylor instability, lithospheric dynamics, surface topography at convergent mountain belts, and gravity anomalies. Journal of Geophysical Research: Solid Earth, 118, 2544-2557.

• OKAYA, D., STERN, T. & DAVEY, F. 2013. A Continental Plate Boundary: Tectonics at South Island, New Zealand, John Wiley & Sons.

• WALTERS, R., PARSONS, B. & WRIGHT, T. 2014. Constraining crustal velocity fields with InSAR for Eastern Turkey: Limits to the block‐like behaviour of Eastern Anatolia. Journal of Geophysical Research: Solid Earth.