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Compositional Stratification in the Deep Mantle

Compositional Stratification in the Deep Mantle. Main things a thermochemical model of Earth’s mantle should address: Produces sufficient heat Produces geochemical signatures of basalts Agrees with seismic tomography Lowermost mantle characterized by long-wavelength structure

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Compositional Stratification in the Deep Mantle

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  1. Compositional Stratification inthe Deep Mantle

  2. Main things a thermochemical model of Earth’s mantle should address: • Produces sufficient heat • Produces geochemical signatures of basalts • Agrees with seismic tomography • Lowermost mantle characterized by long-wavelength structure • Dynamically consistent (what does this mean?)

  3. Approximately 50% of mantle not outgassed • 44 TW total heat flux, only 6 from crust • Evidence from heat flux for distinct geochemical resevroirs? • Calculations show an entire mantle of MORB could not produce needed 38 TW without rapid cooling (and excessive Archean T) • Why do they think the upper mantle is generally (as an entire layer) depleted?

  4. Methods • Finite Element Model with two distinct layers, one with high density • Boundary is at 1600 km • Subducting slab interaction w/ this dense layer • T and P dependent viscosity • Heating mantle from below at CMB, and from within by U, Th, and K decay

  5. Conclusions • What is the “important concept”? • What do the authors point out as potential issues in applying their model to the real Earth?

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