Mantle Melting and Intraplate Volcanism Due to Self‐Buoyant Hydrous Upwellings From the Stagnant Slab That Are Conveyed by Small‐Scale Convection

Abstract

AbstractThe mechanisms sustaining basaltic continental intraplate volcanism remain controversial. Continental intraplate volcanism is often geographically associated with slab stagnation in the mantle transition zone (MTZ), for example, in eastern Asia, central Europe, and western North America. Using 2‐D geodynamic models, we here explore the role of the stagnation of a slab and an associated hydrous layer in the MTZ on the formation and evolution of intraplate volcanism. Due to the intrinsic buoyancy of the hydrous layer atop the stagnant slab, upwellings develop within a few million years and rise to ~410‐km depth. At these depths, they partly lose their intrinsic buoyancy due to dehydration and stall intermittently. However, they are readily entrained by sublithospheric small‐scale convection to reach the base of lithosphere, sustaining mantle melting and intraplate volcanism. Water contents of >0.3 wt.‐% in a ≥ 60‐km‐thick layer atop the slab are sufficient for an early (<~20 Myr) onset of melting to account for volcanism, for example, in NE China. Thus, significant amounts of hydrous materials are not expected to remain stable in the MTZ for geological timescales, consistent with geophysical estimates. To explain the geochemical signatures of the Cenozoic basaltic volcanism in northern China, a mixed composition of the hydrous layer, including an enriched mantle‐type and a hybrid depleted mid‐ocean ridge basalts mantle/high μ‐type component, is required.