Noble gas and carbon studies Noble gas and carbon studies of intraplate volcanoes, strike-of intraplate volcanoes, strike-slip, convergent and divergent slip, convergent and divergent

plate boundariesplate boundaries

Evelyn Füri, December 9th 2008

Introduction

Matterhorn

Tschingelhörner – Glarus thrust

Garnet peridotite Gneiss

Introduction

Geysir, Iceland

R/V AtlantisSIO

Volcan Irazu, Costa Rica

Introduction

The Fluids and Volatiles Laboratory, SIO

• Noble gases (He, Ne, Ar)

• Major volatiles (CO2)

Powerful tools to better understand the evolution of the Earth’s interior, its chemical structure, its volatile fluxes

Questions

• What are the isotopic and elemental distributions of the noble gases

(He, Ne, Ar) in the Earth?

• What do the noble gases tell us about the present geodynamic

structure of the Earth?

Is the mantle layered?

Is there a primordial component left in the mantle?

• What do the noble gases tell us about the history of the Earth

system?

Where did the atmosphere come from?

When did the atmosphere form?

When did the Earth form/differentiate?

Introduction

Introduction

Helium• two stable isotopes: 3He and 4He

Isotopes Isotopes of an element have nuclei with the same number of protons (the same atomic number) but different numbers of neutrons. Therefore, isotopes have different mass numbers.

Kr

Xe

Rn

Ne

Ar

He10

18

36

54

86

2

Noble gases

“inert”

(chemically non-reactive)

Introduction

Helium• two stable isotopes: 3He and 4He

• 3He is “primordial”4He produced by radioactive decay of U and Th

• Measure 3He/4He ratio on a mass spectrometer

Kr

Xe

Rn

Ne

Ar

He10

18

36

54

86

2

Noble gases

“inert”

(chemically non- reactive)

3He is primordial4He produced by radioactive decay of U and Th

Mid-ocean ridge basalts (MORB)

• Degassed (depleted) source

Low 3He content

Low 3He/4He

• Shallow source

Ocean islands basalts (OIB)(e.g. Hawaii, Iceland, Réunion)

• Less degassed (primitive) source

Higher 3He content

Higher 3He/4He

• Deep source? Plume?

Introduction

• Which (if any) of these views of the mantle are correct?

Tackley, Science (2000)

Introduction

Noble gas geochemistry of mantle-derived rocks and fluids on land

Sampling fumarolesSampling hot springs and wells

Mineral separates

Sampling pillow basalts

Mini-DOAS: SO2 flux

Noble gas geochemistry of submarine oceanic basalts

Dredging (R/V Revelle) Pillow basalt fragment with glassy rim

Sampling of submarine cold seep fluids withChemical and Aqueous Transport (CAT) meter

ROV Ventana (Monterey Bay, CA)

DSV Alvin (Costa Rica)

Noble gas geochemistry of cold seep fluids

Monterey Bay (CA)

Fluids associated with the San Andreas and

companion faults have high 3He/4He ratios

Fluids enter the fault system from the

mantle

Kennedy et al., 1997

Monterey Bay

Tryon et al., Oceanographic Research Papers, 2001

Costa Rica

Complete a volatile mass balance for

the Costa Rican Arc

http://www.sfb574.uni-kiel.de/php/goto/Home/

Central Indian Ridge

KNOX11RR, R/V Revelle (NOV 07)

KNOX11RR, R/V Revelle (NOV 07)

Murton et al., G3, 2005

KNOX11RR, R/V Revelle (NOV 07)

Nauret et al., EPSL, 2006

Goals: - Determine the flow pattern of Réunion hotspot material towards the CIR

- Test the hypotheses of Murton et al. (2005) and Nauret et al. (2006)

Murton et al., G3, 2005

KNOX11RR, R/V Revelle (NOV 07)

KNOX11RR, R/V Revelle (NOV 07)

Seafloor mapping:

Multibeam surveying

Instrumentation Viewpoint, Sarti News Bulletin

KNOX11RR, R/V Revelle (NOV 07)

Magnetic surveying

Magnetometerhttps://frontpage.northseattle.edu/jmasura/NaturalDisasters/Science121/SCI03.ppt

KNOX11RR, R/V Revelle (NOV 07)

Dredging

KNOX11RR, R/V Revelle (NOV 07)

~1mm

Results – Heliumon-axis vs. off-axis

The EndThe End

Iceland

Ito, Nature (2001)

Interaction between the Mid-Atlantic Ridge and the Icelandic Hotspot

Bubbling mud pot

Subglacially erupted pillow basalts