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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

Guess?

Measured

Background

velocity

Poiseuille

Stokes


Going down

Background

velocity

Poiseuille

Stokes

Hawaii 7.0 t/s

Bowie 0.3 t/s

All hostpots 55 t/s

Slabs 650 t/s



Going down

M

Mass Balance for trace elements

Primitive Mantle = Crust+Morb source+Hidden res


Rares gas
RaresGas

From Hart & Zindler


Going down

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


Going down

  • 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)


Going down

36Ar(oib)=f 36Ar(pr)

40Ar(oib)=40Ar(sm)


Going down

Hiding a layer:

Viscous stratification

Density and density jumps

Phase changes


Going down

Geoid

Comp. Geoid


Going down

The Mantle viscosity increases with depth by a factor 10-100

Can it help preserving

primitive compositions?


Going down

Hiding a layer:

Viscous stratification

Density and density jumps

Phase changes


Going down

MINERALOGY VS SEISMOLOGY

From Matas


Going down

Hiding a layer:

Viscous stratification

Density and density jumps

Phase changes


Going down

Hotspot (no)

Entrainment

Farnetani or Schmalzl and Hansen





Going down

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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