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Interpreting Geophysical Data for Mantle Dynamics

This study focuses on interpreting geophysical data to understand the dynamics of the Earth's mantle. Wendy Panero from the University of Michigan analyzes the chemical composition, density distribution, and temperature variations in various phases of the mantle. The study provides insights into mantle convection, cold slabs, and the equilibrium of mineral phases.

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Interpreting Geophysical Data for Mantle Dynamics

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  1. Interpreting Geophysical Data for Mantle Dynamics Wendy Panero University of Michigan

  2. 1.0 SiO2 45.4 wt% MgO 37.1 wt% FeO 8.3 wt% Al2O3 4.3 wt% CaO 3.3 wt% Ca-pv opx C2/c cpx 0.8 garnet il Atomic Fraction 0.6 Mg-perovskite 0.4 olivine wadsleyite ringwoodite 0.2 Pyrolite Stacey Geotherm (Mg,Fe)O 0.0 5 10 15 20 25 30 Pressure (GPa) Stixrude, unpublished Chemical Constraints on Density Distribution

  3. Ca-pv cpx garnet il Mg-perovskite olivine wadsleyite ringwoodite (Mg,Fe)O Chemical Constraints on Density Distribution Stacy Geotherm

  4. g-MgSiO4 olivine 440 km 660 km pv+mw b-MgSiO4 1000 200 1400 400 600 1600 exothermic reaction endothermic reaction 800 1700 1000 Cold Slabs, Clapeyron Slopes and Whole Mantle Convection

  5. Clapeyron Slope Equilibrium: DG1=DG2

  6. g-MgSiO4 660 km pv+mw endothermic reaction Cold Slabs, Clapeyron Slopes and Whole Mantle Convection Clapeyron slope must be greater than… ask a geodynamicist

  7. Determination of Clapeyron Slopes Phase Equilibria ex-situ in-situ Thermodynamic

  8. Determination of Clapeyron Slopes Ringwoodite (Smyth) Phase Equilibria ex-situ in-situ Thermodynamic

  9. Multi-Anvil Press

  10. Ringwoodite Only Perovskite + MW Only All present Determination of Clapeyron Slopes Ito and Takahashi 1989 Phase Equilibria ex-situ in-situ Thermodynamic Clapeyron slope = -2.8 MPa/K

  11. Determination of Clapeyron Slopes Ringwoodite (Smyth) Phase Equilibria ex-situ in-situ Thermodynamic

  12. The Laser-Heated Diamond Anvil Cell X-ray Heating laser Pressure = Force/Area 0.1 mm 2 cm X-ray diffraction (pressure, structure, density) Spectroradiometry (temperature)

  13. incoming x-rays, l reflected x-rays, l 2q d Techniques X-ray Diffraction Diffraction condition: l=2dsin(2q) 2q e.g. Cullity

  14. Techniques X-ray Diffraction Ringwoodite Perovskite + periclase

  15. T=1700±75 K Temperature Measurements hotspot gasket O2 ruby (Benedetti et al, unpublished) side view top view Kavner and Panero, PEPI 2004

  16. Pressure Measurements:Equations of State Lee et al., 2004

  17. Constant Temperature Equations of State Bulk Modulus

  18. Constant Temperature Equations of State Lee et al., 2004

  19. PVT Equations of State

  20. Thermodynamic definition Model for internal energy: e.g. Debye PVT Equations of State

  21. Determination of Clapeyron Slopes Shim et al., 2001 Phase Equilibria ex-situ in-situ Thermodynamic Clapeyron slope = -3 MPa/K (Irifune et al., 1998) Clapeyron slope = no constraint (Shim et al., 2001; Chudinovskikh et al., 2001)

  22. Sources of Error Non-hydrostatic stresses Pressure standards Temperature and pressure gradients Diffracted x-ray Incoming x-ray Vhydrostatic<Vnon-hydrostatic diamond diamond

  23. Sources of Error Non-hydrostatic stresses Pressure standards Temperature and pressure gradients Kavner and Duffy, 2003

  24. Sources of Error Non-hydrostatic stresses Pressure standards Temperature and pressure gradients Gold relative to Platinum Shim et al., 2001

  25. Sources of Error Non-hydrostatic stresses Pressure standards Temperature and pressure gradients hotspot gasket O2 ruby (Benedetti et al, unpublished) side view top view Kavner and Panero, PEPI 2004

  26. Determination of Clapeyron Slopes Phase Equilibria ex-situ in-situ Thermodynamic Clapeyron slope = -4±2 MPa/K Ito et al., 1990

  27. Interpretation of Tomography:Thermal Variations

  28. 1.0 SiO2 45.4 wt% MgO 37.1 wt% FeO 8.3 wt% Al2O3 4.3 wt% CaO 3.3 wt% Ca-pv opx C2/c cpx 0.8 garnet il Atomic Fraction 0.6 Mg-perovskite 0.4 olivine wadsleyite ringwoodite 0.2 Pyrolite Stacey Geotherm (Mg,Fe)O 0.0 5 10 15 20 25 30 Pressure (GPa) Stixrude, unpublished Interpretation of Tomography:Compositional Variations

  29. Interpretation of Tomography:Compositional Variations Perovskite Composition K0 (GPa) r (Mg/m3) (km/s) 7.974 MgSiO3 262 4.12 7.851 262 4.25 MgSiO3~10% FeO 7.956 4.123 261 MgSiO3 ~3.25% Al2O3 256 4.088 7.913 MgSiO3 ~3.25% Al2O3+H2O

  30. Theory • Quantum mechanical or classical • effects of a priori assumptions • size of calculation, time for calculation General approach: G of each phase PT-space for lowest energy Limitations: Temperature Multi-component systems

  31. Theory MgSiO3 perovskite Wentzcovitch et al., 2004

  32. Zhao et al., 1992 ?

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