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Magma Ocean Solidification and Formation of a Candidate Terrestrial D Layer Alessondra Springmann April 20, 2011 1 Roadmap Background Methods Results Discussion 2 3 4 142 Neodymium 142 Nd 144 Nd

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SLIDE 1

Magma Ocean Solidification and Formation of a Candidate Terrestrial D” Layer

Alessondra Springmann April 20, 2011

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SLIDE 2

Roadmap

  • Background
  • Methods
  • Results
  • Discussion

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SLIDE 3

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SLIDE 4

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SLIDE 5

µ142 Neodymium

µ142Nd =    142Nd

144Nd

  • sample

142Nd

144Nd

  • standard

− 1    × 1, 000, 000

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SLIDE 6

terrestrial µ142Nd = 0

chondrite µ142Nd = -18

Carlson & Boyet (2008)

EER prediction: µ142Nd = -54

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SLIDE 7

6,378 km 0 km 3,488 km

D” Layer

Adapted from Beatty et al. (1999), p. 114

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SLIDE 8

Measuring the D”

Lay et al. (1998)

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SLIDE 9

perovskite structure post-perovskite structure

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SLIDE 10

Roadmap

  • Background
  • Methods
  • Results
  • Discussion

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SLIDE 11
  • Elkins-Tanton 2008 Model
  • Assume a whole-mantle magma ocean
  • Mineral stability
  • Tracks solidified assemblage, co-evolving

liquid composition

Model

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SLIDE 12

!"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* ,"34#!+"35&'(* !"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* 5,#%&"'(* !"#$#%&'()*6'+"#%!,-.!/&%&'0)* !.12!,-.!/&%&'0)* 43.%&1'7)* !8!"#$#%&'9)* :3;!.#1&'<(* +"#%!,-.!/&%&'0(* ,&.!$5=#1&'>(* :34%&5#!?@51#1&'(*

00 7( 0A( 7 <69>) ) (6>)) B67)) B6<<) B6<C) B 6 < C D 7'E3.

'radius F=:G p.&55@.&'FHI3G

7))

+!.& "8!"#$#%&'9(* :3;!.#1&'((*

B6))) 7D 7C) 96<0)

,!518,&.!$5=#1&'7))*

Mineral Stability by Depth

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SLIDE 13

Mineral Stability by Depth

!"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* ,"34#!+"35&'(* !"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* 5,#%&"'(* !"#$#%&'()*6'+"#%!,-.!/&%&'0)* !.12!,-.!/&%&'0)* 43.%&1'7)* !8!"#$#%&'9)* :3;!.#1&'<(* +"#%!,-.!/&%&'0(* ,&.!$5=#1&'>(* :34%&5#!?@51#1&'(*

00 7( 0A( 7 <69>) (6>)) B67)) B6<<) B 6 < C ) B 6 < C D 7'E3. 7))

+!.& "8!"#$#%&'9(* :3;!.#1&'((*

B6))) 7D 7C) 96<0)

,!518,&.!$5=#1&'7))* !"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* ,"34#!+"35&'(* !"#$#%&'()* +"#%!,-.!/&%&'0(* !.12!,-.!/&%&'0)* 5,#%&"'(* !"#$#%&'()*6'+"#%!,-.!/&%&'0)* !.12!,-.!/&%&'0)* 43.%&1'7)* !8!"#$#%&'9)* :3;!.#1&'<(* +"#%!,-.!/&%&'0(* ,&.!$5=#1&'>(* :34%&5#!?@51#1&'(*

00 7( 0A( 7 <69>) (6>)) B67)) B6<<) B 6 < C ) B 6 < C D 7'E3. 7))

"8!"#$#%&'9(* :3;!.#1&'((*

B6))) 7D 7C) 96<0)

,!518,&.!$5=#1&'7))*

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SLIDE 14

Solidification

  • Magnesium fractionates preferentially out
  • f the melt into solid assemblages
  • Melt becomes enriched in iron
  • Happens rapidly
  • ~104 years

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SLIDE 15

2600 2800 3000 3200 3400 3600 3800 4000 3000 3500 4000 4500 5000 5500 6000 6500 density (kg/m3) radius (km) pre-overturn density

high density low density

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Overturn

  • Unstable density profile
  • Overturn via Rayleigh-Taylor instabilities
  • ~ 2-4 x 106 years

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SLIDE 17

2600 2800 3000 3200 3400 3600 3800 4000 3000 3500 4000 4500 5000 5500 6000 6500 density (kg/m3) radius (km) pre-overturn density post-overturn density

Overturn results in material sorted by density

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SLIDE 18

Roadmap

  • Background
  • Methods
  • Results
  • Discussion

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SLIDE 19

2600 2800 3000 3200 3400 3600 3800 4000 3000 3500 4000 4500 5000 5500 6000 6500 density (kg/m3) radius (km) pre-overturn density post-overturn density depth of the deep dense layer

Deep dense layer: 250 km thick

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SLIDE 20

3300 3310 3320 3330 3340 3350 3360 3370 3380 3390 3400 20 40 60 80 100 120 140 160 180

initial density (kg/m3) change in density (kg/m3)

T = 100 K T = 1000 K T = 2500 K T = 5000 K

Deep dense layer is stable against thermal expansion

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SLIDE 21

terrestrial µ142Nd = 0

chondrite µ142Nd = -18

Carlson & Boyet (2008)

EER prediction: µ142Nd = -54

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SLIDE 22

−200 200 400 600 800 1000 1200 −60 −40 −20 20 40 60 80

mantle 142Nd (ppm) deep dense layer 142Nd (ppm)

0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 Sm partition coefficient in MgFe-perovskite

µ142Nd =    142Nd

144Nd

  • sample

142Nd

144Nd

  • standard

− 1    × 1, 000, 000

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SLIDE 23

Roadmap

  • Background
  • Methods
  • Results
  • Discussion

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SLIDE 24

Candidate D” Layer

  • Composition
  • Initial composition: Hart & Zindler

(1986); Anders & Grevesse (1989)

  • Does not match Carlson & Boyet

(2008) predictions

  • Non-chondritic initial composition?

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SLIDE 25

Candidate D” Layer

  • Physical Properties
  • 3.24% of the mantle by mass
  • Dense
  • 250 km thick
  • Thermally stable
  • Melting in this region likely negatively

buoyant (Knittle 1998)

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Future Investigations

  • Varying of magma ocean depths
  • Different mineral assemblages by depth
  • Varying initial composition
  • Non-chondritic abundances for rare-

Earth elements

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SLIDE 27

Acknowledgements

  • L. T. Elkins-Tanton
  • NSF Astronomy grant to L. T. Elkins-Tanton
  • R. P. Binzel
  • R. W. Carlson

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SLIDE 28

Acknowledgements II

  • J. L. Elliot, J. A. Connor, S. D. Benecchi,
  • F. E. DeMeo, S. J. Vance, A. S. Rivkin,
  • F. Vilas, M. E. Skolnik
  • A. D. Wickert, M. C. Perignon,
  • Z. J. Bailey, E. B. Holmes, M. F. Lockhart,
  • B. A. Black, S. M. Brown, G. T. Farmer, J. Suckale

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Questions?

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... 142 143 144 ... ... 145 146 147 ... ... 142 143 144 ... ... 145 146 147 ...

Nd Sm Nd Sm

t

1 / 2 1 4 6

Sm = 1.03 x 10

8

years

t = 4.567 Ga t = 0 Ga

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