Résumé
Scattered non-age-progressive intraplate volcanism (SIV) is globally widespread, yet its underlying mechanism remains poorly understood. A hypothesis posits that the magma feeding this volcanism originates from hydrous melting of upwelling mantle from the mantle transition zone (MTZ), driven by subduction-induced return flow. Here, we test this hypothesis using a two-dimensional numerical model of passive MTZ upwelling that incorporates magma formation and transport based on two-phase flow theory. Our results show that dehydration of the upwelling MTZ mantle at the 410 km discontinuity initially forms a large, horizontally elongated magmatic solitary wave. Driven by buoyancy, this wave ascends and subsequently disintegrates into multiple, smaller (∼10−20 km in diameter) magmatic solitary waves. These discrete waves ascend randomly through the asthenosphere in a process akin to “mantle rain,” reaching the lithosphere base in ∼10 m.y. Our model provides a viable explanation for SIV.