Recently, a new model for mantle convection was proposed that may be more realistic than previous standard models. Exciting questions remain, of course, but we believe it can be used to reconcile otherwise conflicting evidence from different research fields and thus provide a new framework for further studies of convection.
Drawing on some of our own recent work [Albarède, 1998] and that of others we further explore the model proposed by Kellogg et al. [1999] and Van der Hilst and Karason [1999]. The new view considers that a deep layer, chemically distinct from the overlying layers, occupies roughly the lower third of the mantle. Such a deep layer would host a substantial fraction of the terrestrial heat producing elements and help close the budget of some critical isotopic systems.The subtle trade‐off between chemical and thermal density variations produces significant dynamic topography, which complicates its seismic detection but facilitates downwelling slabs to pierce through it. Thermal plumes would form at the transition between the boundary layer and the overlying part of the convective mantle. Severing the tie between the depleted and less depleted and outgassed reservoirs and the seismologically identified upper and lower mantle, separated by the 660‐km discontinuity, seems to go a long way toward reconciling the otherwise conflicting pieces of evidence.
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