Insight into the origin of the Tengchong intraplate volcano in southwest China from local and teleseismic data

A high-resolution tomographic image of the crust and upper mantle under Yunnan Province in southwest China was determined by using a large number of teleseismic data measured precisely from digital seismograms as well as local earthquake arrival times recorded by the dense Yunnan seismic network. Our resulting model shows a clear low-velocity (low-V) column extending from the surface down to about 400 km depth under the active Tengchong volcano and some high-velocity (high-V) anomalies existing in the mantle transition zone. Furthermore, the low-V anomaly extends horizontally toward the northeast at ~250-400 km depths. We consider that the Tengchong volcano is a subduction-zone volcano caused by the slab dehydration and corner flow in the mantle wedge, though the subducted slab is a continental plate (Burma micro-plate). Our results show that the upwelling flow under Tengchong originates at ~400 km depth. A prominent low-V anomaly along the Red-River fault zone extends down to the upper mantle, reflecting that the Red-River fault zone may have cut through the crust to the upper mantle. The two Dayao earthquakes (M 6.1 and M 6.2) in 2003 occurred on the margin of high-V anomalies and are underlain by a prominent low- V anomaly in the lower crust and upper mantle, suggesting that the Dayao earthquakes may be associated with the deep fluids released from the dehydration of the subducted India slab (or Burma microplate). These results have significantly improved over the previous studies and provided new seismic constraints on the dynamic processes of the India-Asia collision.