The subducted slab of Yangtze continental block beneath the Tethyan orogenin western Yunnan

The western Yunnan area is a natural laboratory with fully developed and be st preserved Tethyan orogen in the world. Seismic tomography reveals a slab -like high velocity anomaly down to 250 km beneath the western Yunnan Tethy an orogen, to its west there is a low-velocity column about 300 km wide. In the region from Lancangjiang to Mojiang an obvious low velocity in the low er crust and uppermost mantle overlies on the slab. Synthesizing the availa ble geological and geochemical results, the present paper demonstrates that this slab-like high velocity anomaly is a part of the subducted plate of Y angtze continental segment after the closure of Paleotethys. The collision of India and Eurasia continent starting from 50-60 MaBP might trigger therm al disturbance in the upper mantle and cause the uprising of asthenosphere, in that case the subducted Yangtze plate could be broken off, causing Ceno zoic magmatic activities and underplating in the Lancangjiang-Mojiang regio n.