Mantle Upwellings Induced by the Stagnant Slabs in the Mantle Transition Zone: A Numerical Study

Lithospheric thinning in the East Asia exhibits a broad spatial correlation with the stagnant slabs in the mantle transition zone (MTZ), and conceptual models have linked them via mantle upwelling, or plumes, from the MTZ. Because the stagnant slabs present a heat sink rather than a source, such mantle upwellings cannot be thermally driven. They are speculated to be driven by dehydration in the MTZ, but the mechanisms remain to be investigated. Here, we use 2D coupled thermochemical-mechanical modelling to explore the dynamics of the chemically driven mantle upwellings and their tectonomagmatic interactions with the overriding plate. We found that the chemically driven mantle upwellings in the upper mantle are generally narrower, faster, and can be stronger than thermally driven mantle upwellings. The chemically driven mantle upwellings can advect heat to the base of the overriding plate to cause thermal erosion and partial melting. Their roles are limited and unlikely to be the major cause of mantle lithospheric thinning in East Asia, but they provide a compelling mechanism for the widespread Cenozoic basaltic magmatism.