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The Core-Mantle Boundary Region Jeanloz & Williams, 1998

The Core-Mantle Boundary Region Jeanloz & Williams, 1998. Lower mantle. Heat flow. CMB. Outer core. Lower mantle mineralogy. Classical constraints. Bulk composition: observed top-most mantle sample; Peridotitic: 50% olivine + 40% pyroxene + minor phases.

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The Core-Mantle Boundary Region Jeanloz & Williams, 1998

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  1. The Core-Mantle Boundary Region Jeanloz & Williams, 1998 Lower mantle Heat flow CMB Outer core

  2. Lower mantle mineralogy Classical constraints Bulk composition: observed top-most mantle sample; Peridotitic: 50% olivine + 40% pyroxene + minor phases Acoustic properties match seismological observation; Is similar to chondritic meteorites; Can produce basalt upon partial melting at low pressures (cf. MOR); …Details are uncertain yet

  3. Lower mantle mineralogy High-pressure experiments Pyroxene Olivine Modified Spinel Garnet Spinel Density Depth (km) Pressure (GPa) Silicates (Solids) D “ layer Metals (liquids) Volume Fraction (%)

  4. Outer core composition Properties are similar to Fe; Among candidates, Fe is most abundant in the universe; Earth’s magnetic field requires electrically conducting fluid; 10% less dense than Fe ‡Fe-rich alloy; (resulting in large uncertainties in the estimated T of CMB)

  5. Thermal profile of Earth melting Temperature geotherm adiabat Depth (km) Pressure (Mbar) [Boehler, 1996]

  6. Thermal profile of Earth A suite of free parameters…. O. Anderson’s recom. Tm of iron Ita & Stixrude ,1994 Ito & Katsura, 1989 Chopelas et al., 1994 OC adiabat Thermal bdry layer? Jump? Thermal bdry layer; Jump? Temperature (K) 600 K jump? 300 K jump? LM adiabat Depth (km) [Kuo & Chen, in prep.]

  7. Chemical reactions at CMB Ultrahigh pressure & temperature experiments [Knittle & Jeanloz, ’86; ‘89] Fe-depleted silicates & Fe alloys: fast and low seismic velocity, respectively; FeO: non-metallic  metal alloy at deep mantle pressure; ( O  metal at > 100 GPa ) Partial melting High T, melting-point depression in metal-silicate system

  8. Igneous & metamorphic processes of CMB Lower mantle Infiltration & reaction zone Liquid metal alloy Outer core

  9. Thermal-chemical boundary layer Lower Mantle (MgFe)SiO2 + (MeFe)O perovskite magnesiowiistite FeO + FeSi D”layer metallic alloys Mixed(?) Thermal and Chemical Boundary Layer Reaction Zone Liquid Fe alloy Outer Core [Knittle & Jeanloz, 1991]

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