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