Slab-Plume Interaction Arrests the Ascent of the Hainan Plume

Volcanic hotspots are commonly attributed to hot mantle plumes rooted at the core-mantle boundary. Yet the absence of expected surface signatures at some hotspots challenges this classical view. Seismic tomography reveals a prominent low-velocity mantle anomaly (named the Hainan plume) beneath the Leiqiong volcanic field; however, this region lacks a linear volcanic chain and shows low 3He/4He ratio, making its genesis highly controversial. Here we integrate receiver-function imaging with mineral physics modeling to reveal the interaction between the Hainan mantle plume and remnant slabs within the mantle transition zone (MTZ). We find that the plume ascends along a low-velocity corridor at the slab edge, while the slab acts as a thermochemical filter, resulting in notable radial stratification within the MTZ. Although a thermal anomaly of 150 K near the 660-km discontinuity indicates plume ponding, this heat dissipates markedly by 410 km depth. Instead, the ascending plume becomes enriched in basaltic components (up to ~60%). We demonstrate that slab-induced cooling and density crossovers drain the plume of its thermal buoyancy, trapping basaltic oceanic crust within the upper MTZ. This results in a low-buoyancy upwelling that limits the plume’s contribution to Leiqiong volcanism. These findings suggest that the ascent of deep mantle plumes can be effectively arrested by ambient mantle heterogeneities, providing a unique explanation for the lack of surface plume signatures at some hotspots.