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GOING DOWN

GOING DOWN. Seismic tomography. GOING UP. Guess ?. Measured. Background velocity. Poiseuille. Stokes. Background velocity. Poiseuille. Stokes. Hawaii 7.0 t/s Bowie 0.3 t/s All hostpots 55 t/s Slabs 650 t/s. GEOCHEMISTRY. M. Mass Balance for trace elements.

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GOING DOWN

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  1. GOING DOWN

  2. Seismic tomography

  3. GOING UP

  4. Guess? Measured Background velocity Poiseuille Stokes

  5. Background velocity Poiseuille Stokes Hawaii 7.0 t/s Bowie 0.3 t/s All hostpots 55 t/s Slabs 650 t/s

  6. GEOCHEMISTRY

  7. M Mass Balance for trace elements Primitive Mantle = Crust+Morb source+Hidden res

  8. RaresGas From Hart & Zindler

  9. 40Argon But K/U?? 50-200 pmol/g Another K-rich reservoir? Produced in the Earth 940 pmol/g Atmosphere 44% Crust 3.5% Upper mantle .9 % (25 pmol/g) Lower mantle 52 % (720 pmol/g) From Davies

  10. OIBs are more heterogeneous than MORBs • But the same trends are seen in MORBs and OIBs • There is a hidden reservoir • Slightly depleted=lower mantle • Primitive=50% of the mantle • Enriched (D'' with MORBs composition)

  11. 36Ar(oib)=f 36Ar(pr) 40Ar(oib)=40Ar(sm)

  12. Hiding a layer: Viscous stratification Density and density jumps Phase changes

  13. Geoid Comp. Geoid

  14. The Mantle viscosity increases with depth by a factor 10-100 Can it help preserving primitive compositions?

  15. Hiding a layer: Viscous stratification Density and density jumps Phase changes

  16. MINERALOGY VS SEISMOLOGY From Matas

  17. Hiding a layer: Viscous stratification Density and density jumps Phase changes

  18. Hotspot (no) Entrainment Farnetani or Schmalzl and Hansen

  19. THERMO-CHEMICAL CONVECTION

  20. Crust density: Mineralogy

  21. Mantle, Lithosphere and oceanic crust

  22. No real geochemical indication of the existence of primitive material Strong indications that the 670 km depth boundary is permeable Strong indications of a viscosity increase with depth by 10-100 This viscosity increase does not stratify the mixing 3D convection more efficient mixer with, than without plates Highly viscous, small, primitive blobs may survive(?) Need of a reservoir to store incompatible elements Seems difficult to hide a dense reservoir in the mantle Crust segregation in D'' may be the deep enriched reservoir (EM, HIMU) The remaining lithosphere may be the depleted (''primitive-like'') reservoir

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