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The Plume‐Hotspot Connec2on, Plate Tectonics and the Remarkable Character of the CMB Region: A global perspec2ve on mantle heterogeneity Mark Jellinek University of Bri2sh Columbia
The Plume‐Hotspot Connec2on, Plate Tectonics and the Remarkable Character of the CMB Region:
A global perspec2ve on mantle heterogeneity
Mark Jellinek University of Bri2sh Columbia
Kellogg et al. (1999)
Jellinek and Manga (2004)
Tackley (1998, 2000)
Davaille (2002)
A selec've anthology of cartoons related to global T and C heterogeneity: Different pictures, different goals
Tackley (2008)
Stacey, 1992
Li and Zhong (2009) T & C heterogeneity: concepts
⇒ “Inherent”: Ini2al mantle composi2on and structure ⇒ Introduced at the boundaries via subduc2on and plume rise ⇒ Modified by mantle s2rring, phase changes and differen2a2on processes (e.g., mel2ng)
Some Mo'va'ons ⇒ Hidden ICE reservoir (e.g.,142Nd/144Nd, missing 40Ar) ⇒ Superswells ⇒ Variable slab penetra2on and mantle layering ⇒ Plates, plumes, CMB structure ⇒ Supercon2nent cycles and plume/LIP frequency ⇒ Magne2c field structure and dynamics ⇒ Earth’s various wobbles
Kellogg et al. (1999)
Jellinek and Manga (2004)
Tackley (1998, 2000)
Davaille (2002)
A selec've anthology of cartoons related to global T and C heterogeneity: Different pictures, different goals
Tackley (2008)
Stacey, 1992
Li and Zhong (2009) T & C heterogeneity: concepts
⇒ “Inherent”: Ini2al mantle composi2on and structure ⇒ Introduced at the boundaries via subduc2on and plume rise ⇒ Modified by mantle s2rring, phase changes and differen2a2on processes (e.g., mel2ng)
Kellogg et al. (1999)
Jellinek and Manga (2004)
Tackley (1998, 2000)
Davaille (2002)
A selec've anthology of cartoons related to global T and C heterogeneity: Different pictures, different goals
Tackley (2008)
Stacey, 1992
Li and Zhong (2009) What do we see, how do we see it?
Which of these pictures do “the data” permit?
Which of these pictures do “the data”demand?
How do we choose one…?
Concluding Remark: Heterogeneity in the plume source region is inherited from the beginning, introduced at the boundaries and modified by 2me‐dependent mantle s2rring
Building understanding of the T & C heterogeneity story told by ocean islands: ⇒ Early Earth differen2a2on ⇒ Mantle Structure (mineral physics) ⇒ Plate tectonics and supercon2nent cycles: Mantle S2rring ⇒ Thermochemical mantle plumes ⇒ Geodynamo ⇒ Climate and climate variability over long 2me scales ⇒ Dynamics of mel2ng, extrac2on and magma mixing in the mel2ng region
“Earth system science”: A key to making progress ⇒ Involve mul2ple classes of observa2onal constraint in a rigorous and restric2ve way.
Spherical Harmonic Degree
Power
Big (deg. 1 => ~ Earth Circumference)
Scale at which a class of heterogeneity goes “IN” to mantle flow
Scale “OUT” (e.g., by diffusion)
Resolu2on Limit: Smallest thing we can resolve with a given method
Small (deg. 1000 => ~ Earth Circumference/1000)
A global mixing problem: Characterizing and understanding T & C Heterogeneity length scales through 2me
To what extent can current global seismic imaging constrain geodynamic models?
Ritsema et al, 2007
Chemical layering introduced by subd: mel2ng, phase changes etc. (via PERPLEX + new min phys)
Red: Tomography Ritsema, 2004 Blue: Bull et al., 2009 Preferred
Nakagawa et al., 2010
Tomographic “filtering” of two geodynamic models => combined T & C spectra from models with dis'nct ini'al mantles are not very different
Deep Mantle Only
“Primordial” Chemical Layering: Pyrolite + density perturba2on
Vsurf Strain Rate
Con2nents =>
T, Plates, Plumes =>
A State‐of‐the‐art model: What do we want out of this?
⇒ What specific predic'ons would we like to make? ⇒ What data sets do we require? Höink et al., in prep
Understanding L‐ and t‐scales: What are some of the physical problems involved?
Heterogeneity from ini'al core/mantle diff. • Radial mantle structure: Composi2on; rheology; Incompa2ble element distribu2on
Heterogeneity introduced at boundaries Surface Plates • Wavelength and shape: Lg. scale mantle s2rring • Ver2cal structure: Mean T; Comp.; Rheology • Subduc2on physics and plate boundary rheology • Con2nents: Thermal and mechanical effects • Slab/wedge/asthenosphere mineral Physics: Mel2ng; Degassing; Phase changes etc. • Ridge hydrothermal processes • Climate/ocean variability on long 2me scales
CMB region: Mantle Side • Lateral and ver2cal structure: Composi2on; Rheology • Mantle plume physics w/, w/o C‐layering • Mineral Physics: Mel2ng; phase changes; P‐dependent phys. Props, etc. • Dynamo: Existence, dynamics and structure of M‐field • Rota2onal dynamics at all 2me scales (TPW => LOD)
Heterogeneity spectrum modified internally • Mantle conv. regime: S2rring to small scales • Radial mantle structure: Density; rheology
Heterogeneity from ini'al core/mantle diff. • Geochemical Mass Balances and BSE • Inner core size, age • Paleointensity over the age of Earth • Time‐averaged magne2c field structure
Heterogeneity introduced at boundaries Surface Plates • Plate reconstruc2ons (including age distribu2on) • Maps: seafloor composi2on, g, topography, Telas2c, mag., stress, heaolow, permeability, conduc2vity, etc. • Seismology: Plate structure, anisotropy, damage etc. • Arc Volcanism: Erup2on rates, distribu2on, composi2on • MORB & OIB geochemistry • Chemical cycles (e.g., C, S, others) • Geometry and composi2on of ridge hydrothermal systems • Mineral Physics CMB region • Ver2cal and lateral seismic velocity structure • Spa2al Correla2ons: HS and heterogeneity; Pacific sec. var • Variable HS B‐flux / excess T & OIB geochem • Time‐averaged magne2c field structure • Magne2c reversal frequency ; VGP behavior • Earth’s “wobbles”: g and EM coupling across CMB • Inner core structure, size and age • Mineral physics (incl. TE par22oning) • Climate variability over long 2me scales
What are some constraints?
Heterogeneity from ini'al core/mantle diff. • Geochemical Mass Balances and BSE • Inner core size, age • Paleointensity over the age of Earth • Time‐averaged magne2c field structure
Heterogeneity introduced at boundaries Surface Plates • Plate reconstruc2ons (including age distribu2on) • Maps: seafloor composi2on, g, topography, Telas2c, mag., stress, heaolow, permeability, conduc2vity, etc. • Seismology: Plate structure, anisotropy, damage etc. • Arc Volcanism: Erup2on rates, distribu2on, composi2on • MORB & OIB geochemistry • Chemical cycles (e.g., C, S, others) • Geometry and composi2on of ridge hydrothermal systems • Mineral Physics CMB region • Ver2cal and lateral seismic velocity structure • Spa2al Correla2ons: HS and heterogeneity; Pacific sec. var • Variable HS B‐flux / excess T & OIB geochem • Time‐averaged magne2c field structure • Magne2c reversal frequency ; VGP behavior • Earth’s “wobbles”: g and EM coupling across CMB • Inner core structure, size and age • Mineral physics (incl. TE par22oning) • Climate variability over long 2me scales
What are some constraints?
What is the story told by ocean islands?
⇒ Thermal regime: Plate tectonics, lower mantle chemical heterogeneity and the structure of plumes
⇒ Composi'on: Entrainment physics
⇒ Some key constraints (real and imagined)
Cold thermal boundary layer!
Hot thermal boundary layer!
Sets Lower Boundary !Layer Temperature &!Viscosity Variation!
Determines !Thermal &!Velocity BL!Structure!
and!
Upwelling !Morphology!
Plate Tectonics!is a 1st-Order!Control on CMB!Dynamics !
Montelli et al., 2004
Plume Heads and Tails Plume/Hotspot Taxonomy: Shape and strength vary
Hotspots and Topography on Chemical Piles (see Thorne et al., 2004)
Duncan and Richards, 1990
Williams and Garnero., 1998
Supercon'nent cycles and LIP events: ‐Time‐dependent T & C mixing ‐Length scales vary episodically over geological 2me
Zhong et al., 2007; Li et al., 2009
Supercon'nent Cycles and long‐term climate change (Lenardic, Jellinek et al., in prep)
Key Features of Cretaceous: 1) 100 Myr “Hothouse” (mostly) 2) High LIP Frequency 3) Variable Reversal Frequency:
a) High Frequency during Jurassic; b) K –superchron
4) CAMP & NAVP
Models: 1) Enhanced outgassing 2) “Strong subduc2on” and
subcon2nental warming 3) a)High equatorial CMB heat
flow. b) Low, asymmetric equatorial CMB heat flow
4) Mantle thermal “isola2on to mixing”
Supercon'nent Cycles: Long‐term climate change, LIP frequency and the geodynamo
Observa'ons and inferences: Plumes and the structure of the CMB region
Do we really see plumes extending to (or near) the CMB in tomographic models? (Boschi, Becker and Steinberger, 2008)
Sta2onary HS source
Moving HS sources
“Large Low Shear Velocity Provinces” (LLSVPs): Africa and Pacific features are dis2nct in thickness and possibly density
Ni et al. 2002
(Ni and Helmberger, 2003)
Deschamps et al., 2007
Composi'onal effects dominate the heterogeneity spectrum at long wavelengths near CMB
“Ultra Low Velocity Zone” (ULVZ): 6‐30% par2al melt; metallic conductance
Asymmetries in departures from GAD in TAF: normal vs. reversed
(0 ‐ 5 Myr) Johnson et al., 2004
Magne2c field behavior sensi2ve to CMB thermal structure
Brunhes: Normal Matuyama: Reversed
Time‐averaged field structure: Persistent Varia2ons in la2tude and longitude
Variable reversal rates & large dipole moment during K‐superchron
Aubert, Tarduno and Johnson, 2010
(Aubert, Tarduno and Johnson, 2010)
Some of the dynamics of the CMB region and some predic'ons
Simple Composite
Tm
TBL
DL
K1 , d1
K2 , d2
Tc
Ti
Core
TBL K1 , d1
Tc
Tm
qcore= f(Ram)
Composite + convection
TBL
DL
Tm
Ti
Tc
qcore= f(Ram , Bi)
Se]ng up a heat transfer problem at CMB: 3 classes to start with
qcore= f(Ram , Bieffective, B, λd)
TiDL
Ritsema, 2004
What are the excess temperatures carried by plumes? Why do they vary spa'ally?
‐ Stable topography possible. ‐ Convec2on(t) ‐ Entrainment(t)
V1(t)
V2(t), M2(t)
‐Large amplitude oscilla2on i.e. A ≥ d. ‐Entrainment / mixing: Oscilla2on is assymetric.
h2(t) M2(t)
B
qcore= f(x,t) qcore= f(x,t)
V
‐Cusp‐like topography ‐ Stable plumes on topography ‐ Steady flow in TBL ‐ Entrainment from DL
qcore= f(x,t)
0.5 1.0
Davaille et al., 2005 Jellinek and Manga, 2004
Dense layer dynamics: Role of comp/thermal buoyancy ra'o in lab experiments
λd >1
λd <1
Davaille, 1999; Davaille et al., 2005
Doming Stra2fied
λd << 1
=> How does the dense layer behave in 'me? How long will it last?
Convec2on(t): TBL, DL Entrainment into both
V1(t)
V2(t), M2(t)
Oscilla2on & (assymetric) Entrainment
h2(t) M2(t)
B
qcore= f(x,t) qcore= f(x,t)
V
Steady flow in TBL Entrainment from DL Spa2ally‐stable plumes
qcore= f(x,t)
0.5 1.0
McNamara and Zhong, 2005 and PC
Dense layer dynamics in a sphere: Similar
Some thermal effects of the dense layer dynamics: • Plume structure and excess temperature (and their global variability) • Plume frequency • Time‐dependence: Supercon2nental cycles and incomplete mantle thermal mixing
2 Plume Types in 1 Mantle: Variability in plume structure NOT a surprise (Lenardic and Jellinek, 2009)
-Chemical Layer Absorbs Portion of CMB Temperature Drop
-Alters Local Viscosity Contrast Across Active Part of Lower Thermal Boundary Layer
-Leads To Two Morphologic Plume Types
-Variations in layer Thickness or effective K with mantle stirring Lead to changes in B-flux And excess T.
Diapir !Plume!
Cavity !Plume!
after Olson & Singer 1985
time evolution
Chemical Pile!
B >> 1
Hawaiian‐Emperor seamounts: An abrupt 4‐5 fold reduc2on in dense layer thickness?
Vidal and Bonneville, 2004
Some of the composi'onal effects of the dynamics of the CMB region: • Plume composi2on: Entrainment from chemical piles and ULVZ material.
Bull et al., 2009
Isotopic variability in erupted lavas may constrain the heterogeneity spectrum of the source region* (Farnetani and Hoffman, 2009, 10; see also Kerr and Meriaux, 2004)
*depending on the magma mixing proper2es of the mel2ng region!
McNamara et al., 2010
Entrainment from chemical piles (LLSVP)
Jellinek and Manga, 2004
Temperature
Composi2on
Kea‐Loa trend: Bilateral asymmetry in HI plume?
Is the Loa trend indica've of the composi'onal structure of chemical piles?
Why did the Loa trend emerge only about 4 million yrs ago?
Why is their greater isotopic variability in the Loa basalts?
Hernlund and Jellinek, 2010
ULVZ Entrainment physics: What is being entrained?
ULVZ
ULVZ entrainment Currently: Homogeneous sampling; Past: Probably not
Early Earth Current ULVZ
Hernlund and Jellinek, 2010
R=10 R=0.1
Past: Larger H Current picture
Buffet et al., 2002 and PC
Nuta2ons (EM coupling across CMB): Sloshing coffee cup
VGP paths during reversals (Cos2n and Buffet, 2003)
ULVZ proper'es: Par'al melt‐outer core interac'on => metallic conductance
Evidence of ULVZ in the plume source? Entrainment of a par'al melt with a lible core material?
Modified from Brandon et al., 1999
MORB
Plume
Outer core signature in plume source?
See Helffrich and Kaneshima, 2010
Evidence of ULVZ in the plume source: TE signatures depend on origin of the ULVZ
Hirose et al., 2004
Labrosse et al., 2007
ULVZ from BMO (normalized to BSE)
ULVZ from mel2ng CaPv in N‐MORB crust (Normalized to N‐MORB)
Concluding Remark: Heterogeneity in the plume source region is inherited from the beginning, introduced at the boundaries and modified by 2me‐dependent mantle s2rring
Building understanding of the T & C heterogeneity story told by ocean islands: ⇒ Early Earth differen2a2on ⇒ Mantle Structure (mineral physics) ⇒ Plate tectonics and supercon2nent cycles: Mantle S2rring ⇒ Thermochemical mantle plumes ⇒ Geodynamo ⇒ Climate and climate variability over long 2me scales ⇒ Dynamics of mel2ng, extrac2on and magma mixing in the mel2ng region
“Earth system science”: A key to making progress ⇒ Involve mul2ple classes of observa2onal constraint in a rigorous and restric2ve way.
Kellogg et al. (1999)
Jellinek and Manga (2004)
Tackley (1998, 2000)
Davaille (2002)
A selec've anthology of cartoons related to global T and C heterogeneity: Different pictures, different goals
Tackley (2008)
Stacey, 1992
Li and Zhong (2009) What do we see, how do we see it?
Which of these pictures do “the data” permit?
Which of these pictures do “the data”demand?
How do we choose one…?
