Key New Evidence for the Hainan Mantle Plume Head: Ongoing Formation of a Large Igneous Province?

Abstract The process‐based surface magmatic expression of mantle plumes is typically a large igneous province (LIP) induced by the mantle plume head, followed by subsequent age‐progressive volcanic tracks resulting from plate drifting above the plume tail. However, although plume‐like low velocity structures have long been observed below Hainan, the magmatic evidence for the mantle plume head or tail remains absent in the surrounding area, which left the existence of the Hainan mantle plume debated yet. Here, we identify volcanism derived from a hybrid source of Hainan plume and lithospheric base, 700 km away from the Hainan plume conduit, based on the submarine seamount basalt obtained by a submersible. This volcanism coincides with the most extensive eruption episode of the Hainan basalt and occurs beneath a thicker lithospheric lid than that of the Hainan basalt. Consistent with the seismic tomography of low velocity zone beneath the lithosphere, this seamount basalt serves as the key magmatic evidence for the interaction between the Hainan mantle plume head and the northern South China Sea (N‐SCS) continental lithosphere. We further demonstrate that the basalt that primarily fractionated within the lower crust was seismically detected as a high‐velocity body. Therefore, it is highly likely that a mantle plume head is responsible for the large volume of igneous rocks on the N‐SCS (at least 150,000 km 3 ), comparable with LIPs (>100,000 km 3 ). The N‐SCS region now may be under the mantle plume head stage and, together with the Hainan basalts, belong to an active LIP.