PHY100H1 Lecture Notes - Thermal Expansion, Eastern Partnership, Digital Signal 0
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Main argument for layered convection: the chemistry of the upper mantle is not chondritic . Lava flows from mid ocean ridges (which sample the upper mantle) seem to be missing some fraction of elements and isotopes we would expect if the earth formed from the solar nebula. People have therefore suggested that the earth has a hidden reservoir of these elements. Because of the phase boundary at 670km depth, the layer below (the lower mantle) would be an ideal location for this hidden reservoir: hot spot lava also has a different chemistry than mid ocean ridge lava. If the lower boundary layer is the 670km discontinuity, then that suggests mantle convection is layered, if it"s the core mantle boundary, then that suggests whole mantle convection. Neither strong layering nor simple whole mantle convection. More difficult to image but with better data, better coverage, and better inversion theory the next decade may show major progress (montelli et al. , gji, science, 2004)