The eclogite engine; Top-down geochemistry

Abstract

Properties of Bullen's Region C (400-1000 km) are used to test mantle stratification models (whole-mantle, two-layer, superplume, marble-cake, hole-in-the-floor, water-filter). Top-down models involving eclogite and continent recycling plus irreversible deep subduction [1, 2] are favored. Density-velocity correlations, transition zone (TZ) thickness and petrology imply radial and lateral changes in lithology and homologous temperature. Injection of warm lower crust into the mantle [3] explains the volume, and compositions, of hotspot magmatism. Massive crustal delamination has previously been ignored in favor of plume injections of ancient MORB.

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