determining the nature of the llsvp
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Determining the nature of the LLSVP. Post-AGU CIDER Workshop 2012 Maxim Ballmer, Jamie Barron, Rohan Kundargi , Curtis Williams, Rick Carlson, Jasper Konter, Jackie Li, Sujoy Mukhopadhyay. Motivation. Why LLSVPs?. - PowerPoint PPT PresentationTRANSCRIPT
Determining the nature of the LLSVP
Post-AGU CIDER Workshop 2012Maxim Ballmer, Jamie Barron, Rohan Kundargi, Curtis Williams, Rick Carlson,
Jasper Konter, Jackie Li, Sujoy Mukhopadhyay
MotivationWhy LLSVPs?
Early Enriched Reservoir = ???= LLSVP ?
Upper Mantle / Lower Mantle
Continental Crust
Bulk Silicate Earth = ???
(1) “hidden” geochemical reservoir (2) secular evolution of the Earth
Lee et al. (2010)
Labrosse et al. (2007)
What are the LLSVPs?Seismic tomography shows two large low shear velocity regions in the lowermost mantle: a degree 2 pattern centered on the Pacific and Africa
Garnero et al. (2007)
- MORB + harzburgite- Pyrolite- MORB alone- Ancient Fe-enriched oceanic crust
- Magma Ocean Product <= team BMO- Perovskite/Magnesiowüstite crystallization
- Magma Ocean Cumulate- KREEP-like- Fe-rich differentiate
- Early Enriched Reservoir- calculated from volumes of LLSVPs and BSE-estimates
Brandenburg and van Keken (2007)Labrosse et al. (2007)
Tackley (2011)
Scenarios of LLSVP origin
(3) Hybrid Scenario
(1) Primitive Reservoir
(2) Slab Graveyard
Calculate physical properties(Jackie Li’s code and/or BurnMan)
Density Vp Vs
Geodynamical test Seismological test
Mg/Si-group
Team BMO
Plan of Attack
(3) Hybrid Scenario
(1) Primitive Reservoir
(2) Slab Graveyard
Calculate physical properties(Jackie Li’s code and/or BurnMan)
Density Vp Vs
Geodynamical test Seismological test
Mg/Si-group
Team BMO
Plan of Attack
(3) Hybrid Scenario
(1) Primitive Reservoir
(2) Slab Graveyard
Calculate physical properties(Jackie Li’s code and/or BurnMan)
Density Vp Vs
Geodynamical test Seismological test
Mg/Si-group
Team BMO
Plan of Attack
calculate volumesof LLSVPs from seismic images
LLSVP volume - choosing contours
Choose contour so it goes through region of steep gradient at edge of LLSVP(compositional change should be associated with sharp gradient)
saw24b160.6% contour
S40RTS0.4% contour
S362ANI0.6% contour
LLSVP volume – choosing height
From clustering analysis – all models show change in gradient for slow cluster at approximately the same depth, around 2100km.
Lekic et al (2012)
LLSVP volume – prel. resultsCalculate the volume within isosurface chosen for model, from CMB to 2100km depth
next step:consider structure that is continuous from CMB only
geodynamic test
760 temperature [°C] 3800
Heig
ht a
bove
CM
B
-basal layer with intrinsic negative buoyancy
- and with excess radiogenic heat production that decays over model time
Gyrs after solidification of basal reservoir
2D models with a resolution of 96x192 elements
Key ingredients:
dense, radio-active material
geodynamic test
760 temperature [°C] 3800
Heig
ht a
bove
CM
B
-basal layer with intrinsic negative buoyancy
- and with excess radiogenic heat production that decays over model time
Gyrs after solidification of basal reservoir
2D models with a resolution of 96x192 elements
Key ingredients:
- As soon as basal-layer material enter the upper mantle, it looses its exceptional properties (density, )
dense, radio-active material
numerical parameter study
10
10
10
10
10
Δρ(basal layer) [g/cm3] Δρ(basal layer) [g/cm3]
Early Enriched Reservoir makes up 11% of the initial mantle
Model time: 4 Gyrs Model time: 4 Gyrs
Initi
al h
eat p
rodu
ction
In b
asal
laye
r [W
/kg]
0.8 1.0 1.2 1.4 0.8 1.0 1.2 1.410
numerical parameter study
10
10
10
10
10
Early Enriched Reservoir makes up 11% of the initial mantle
Model time: 4 Gyrs Model time: 4 Gyrs
Δρ(basal layer) [g/cm3] Δρ(basal layer) [g/cm3] Initi
al h
eat p
rodu
ction
In b
asal
laye
r [W
/kg]
0.8 1.0 1.2 1.4 0.8 1.0 1.2 1.410
…
trace-element concentrations and isotopic ratios in Early Enriched Reservoir
numerical parameter study
10
10
10
10
10
Early Enriched Reservoir makes up 11% of the initial mantle
Model time: 4 Gyrs Model time: 4 Gyrs
Δρ(basal layer) [g/cm3] Δρ(basal layer) [g/cm3] Initi
al h
eat p
rodu
ction
In b
asal
laye
r [W
/kg]
0.8 1.0 1.2 1.4 0.8 1.0 1.2 1.410
outlook- good plan, but quite a lot of
work remains to be done
- rule out a couple specific hypotheses for the composition of the LLSVPs
- perhaps rule out a family of hypotheses for their origin (e.g. the slab graveyard hypothesis)
- present results at EGU 2013
- semantics (LLSVP, BAR, MOP)
CompositionalModels
Compute Physical
Properties
Geodynamic & Seismic Test