Intraplate volcanism and mantle dynamics of Mainland China: New constraints from shear-wave tomography

We determine a new model of S-wave velocity (Vs) tomography beneath Mainland China and surrounding areas by inverting 321,666 S-wave arrival times from 15,618 events recorded by the China Seismic Network (CSN) and at stations in East Asia compiled by the International Seismological Center (ISC). The obtained 3-D Vs model has a generally good resolution down to the uppermost lower mantle, which provides important constraints on the deep structure and origin of intraplate volcanoes in Mainland China. We find a prominent low-Vs body in the upper mantle beneath the Tengchong volcano, which is caused by subduction and rollback of the Burma microplate (or the Indian plate) as well as regional extension of the overriding Eurasian plate. A low-Vs structure is visible beneath the Hainan volcano and it is dominant in two localized zones: one is near the 410-km discontinuity and the other is in the shallow mantle. This feature is compatible with results predicted by the thermochemical plume model. Our Vs tomography reveals a gap between the subducted Indian slab and the Tarim lithosphere beneath the Ashi volcano in northern Tibet, suggesting that hot mantle upwelling could pass through the gap to feed the volcanism in the Ashikule Volcanic Basin. The Datong volcano is underlain by a broadly inclined low-Vs anomaly extending to a depth of similar to 410 km, which possibly reflects focused upwelling produced by avalanche of the stagnant Pacific slab from the mantle transition zone (MTZ) to the lower mantle.