Mantle Transition Zone Structures Beneath SE Tibet Revealed By Receiver Functions

The subduction of the Burman (or Indian) Plate under SE Tibet and its related vol-canism in Tengchong is important tectonic events accompanying the evolution of the Tibetan Plateau. Pervious studies shows that Burman plate subducted into mantle tran-sition zone (MTZ) reaching-660 km. The bot upwelling extend form～410 km to surface beneath Tengchong volcano. But it is still in debate whether the subduction and volcanism are constrained in upper mantle or extend deeply in the MTZ. Here, we imaged the MTZ structure by using receiver function methods with the waveforms recorded by 398 temporary stations deployed by ChinArray project, CSN and IRIS DMC in SE Tibet. We found significant depression of both 410- and 660-km disconti-nuities as well as thickened MTZ (260-280 km) in the western region (i.e.,<104°E) of SE Tibet. The depression of the 660-km discontinuity (by 10-30 km) and thicker MTZ correlate well with high velocity anomalies in the MTZ, suggesting the subducted In-dian slab has reached the MTZ or even sank into the lower mantle. Significant depres-sion of the 410-km discontinuity (by 10-20 km) right beneath the Tengchong volcano. This feature indicate that increased water content of wadsleyite dehydrate more water when transform to a-olivine, and then formed a melting layer atop d410 with higher temperature, which result in depressed d410. Our results confirm the deep subduction of the Burman (or Indian) plate and provide new insight into low velocity anomalies beneath Tengchong volcano.