Phase Transitions in the Lowermost Mantle

Transcription

1 Phase Transitions in the Lowermost Mantle S.-H. Dan Shim 1, B. Grocholski 2, K. Catalli 3, and V. Prakapenka 4 1 Arizona State University, 2 Smithsonian Institution, 3 Livermore National Lab 4 University of Chicago Thanks to: NSF, DOE, NNSA

2 Post-Perovskite Transition MgSiO 3 Murakami et al. (2004) Science, Oganov and Ono (2004) Nature, Shim et al. (2004) GRL The perovskite post-perovskite transition was found at the pressuretemperature conditions similar to those of the D" discontinuity.

3 Discontinuity and Phase Boundary

4 Discontinuity and Phase Boundary Depth vs. Pressure Thickness vs. Width of mixed phase region

5 Compositional Effects Pressure (GPa) % Fe 2+ (C09) Al-free, Fe-bearing systems 20% Fe 3+ (C09) 10% Fe % Al (C09) Al-bearing systems Experiment D" discontinuity Mantle Core Elevation from CMB (km) Δ Pressure (GPa) MgSiO 3 Computation MORB Al (A05) Δ Depth (km) Both Al and Fe 2+ increase the thickness of the transition much greater than that of the D" discontinuity Catalli et al. (2009) Nature

6 Compositional Effects Pressure (GPa) % Fe 2+ (C09) Al-free, Fe-bearing systems 10% Fe 2+ (M04) 20% Fe 3+ (C09) 10% Fe % Al (C09) Al-bearing systems Fe + Al (A10) Experiment D" discontinuity 25% Al (T05) Mantle Core 15% Fe % Al (N07) Elevation from CMB (km) Δ Pressure (GPa) ~SCO (C08) MgSiO 3 Fe 2+ (O05,M05,C05) Al (O05,C05,Z06) Computation MORB Al (T08) Al (A05) Δ Depth (km) Catalli et al. (2009); Mao et al. (2004); Andrault et al. (2010); Tateno et al. (2005); Nishio-Hamane et al. (2007); Caracas et al. (2008); Ono and Oganov (2005); Mao et al. (2005); Caracas et al. (2005); Zhang and Oganov (2006); Tsuchiya et al. (2008); Akber-Knutson et al. (2005) Both Al and Fe 2+ increase the thickness of the transition much greater than that of the D" discontinuity

7 Element Partitioning Wadsleyite (β) Fe Majorite Olivine (α) Post-Perovskite Fe Ferropericlase Perovskite Irifune et al. (1998) Nature Thickness of a phase transition can be decreased significantly by element partitioning with phases which do not participate the phase transition.

8 Mantle Rocks

9 Experiments Crystalline (San Carlos olivine), Glass (Pyrolite and MORB) starting materials Ar/Ne medium, Gold pressure scale Two different types of measurements Heating of fresh starting materials Reversal measurements

10 Perovskite Post-perovskite Grocholski et al. (2012) PNAS

11 Composition Comparison Fe in Pv Al 2 O 3 in Pv Ferropericlase Pyrolite ~10 mol% 5 mol% ~30 mol% San Carlos olivine ~10 mol% 0 mol% 50 mol%

12 San Carlos Olivine Grocholski et al. (2012) PNAS Sharp post-perovskite transition in San Carlos olivine

13 Pyrolite Grocholski et al. (2012) PNAS Broad post-perovskite transition in a pyrolitic mantle

14 Comparison Grocholski et al. (2012) PNAS

15 Composition of MORB MORB has a very large amount of Al and Si

16 Composition of MORB MORB has a very large amount of Al and Si

17 MORB Grocholski et al. (2012) PNAS Sharp, shallow post-perovskite transition in MORB

18 Comparison Grocholski et al. (2012) PNAS MORB has a shallow post-perovskite boundary

19 Mineralogy of Mantle Rocks MORB contains large amounts of Al-bearing minerals

20 Mineralogy of Mantle Rocks MORB contains large amounts of Al-bearing minerals

21 Mineralogy of Mantle Rocks MORB contains large amounts of Al-bearing minerals

22 Element Partitioning Less Al More Al Harzburgite Perovskite Fe Ferropericlase Post-perovskite Pyrolite MORB Perovskite Al Fe Ferropericlase Post-perovskite Perovskite Silica Al Fe,Al CF phase Post-perovskite

23 Summary of Results Grocholski et al. (2012) PNAS MORB or high Mg/Si materials more likely have detectable postperovskite transition in the lower mantle

24 Phase Boundary in Silica Grocholski et al. (2012) under revision Modified Stishovite (CaCl 2 type) Seifertite in MORB, sediments, and core-mantle reaction products

25 Shear Wave Velocity _ Stishovite CaCI Colum.11 C,, C " 800 8OO Cl 2 60O 400 ø. 4O0 --, i, Pressure (GPa) Karki et al. (1997) GRL Shear wave velocity decreases at the silica phase transition in D"

26 Double Discontinuity Structures Thermal Probe Chemical Probe

27 Future Work

28 Future Work Element partitioning among different minerals.

29 Future Work Element partitioning among different minerals. Exploration of other compositions, chondritic, solidified mantle melts, etc.

30 Future Work Element partitioning among different minerals. Exploration of other compositions, chondritic, solidified mantle melts, etc. Mineralogy of the lower mantle.