New seismic constraints on the upper mantle structure of the Hainan plume

Abstract

We present a high-resolution tomographic image in the upper mantle for the Hainan plume determined by using both local and teleseismic data. The arrival-time data from teleseismic events are measured precisely from seismograms recorded by nine permanent seismic stations in Hainan island and Leizhou peninsula. Our results show that striking low-velocity (low-V) anomalies of up to −5% in the crust and −2% in the mantle are visible under the Hainan hotspot from the surface down to 250km depth. The Hainan plume is imaged as a continuous, NW–SE tilting, low-V column with a diameter of about 80km. Given the denser data coverage and finer parameterization, our result represents a significant improvement with respect to earlier, regional and global tomographic studies. Such an inclination of the Hainan plume can be explained by numerical simulations. The tilted plume conduit in the upper mantle could be associated with the subduction of oceanic plates, especially the Philippine Sea plate, and the extrusion of the Eurasian plate. Most likely, the tilted plume conduit has buoyantly risen from the lower mantle.