Seismic Features of the Crust-Upper Mantle Beneath Karamay-Kuqa, Xinjiang

The results from receiver function and ACH inversion indicate that, driven by the collision between Eurasia and India, crustal shortening and thickening is ongoing in Xinjiang, which induces continuous uplifting of Tian Shan and the high density cold crust underneath the Junggar block and Tarim block to dive under the Tian Shan low velocity body. Yet the two-way subduction is unsymmetrical, being steep in the north and less steep in the south, the two meeting at the depth of about 200km. The jointed subduction turns nearly vertical at the depth of 250km, which goes further down to 350km with a possibility of detachment. This unsymmetrical diving pattern may well be the evidence that the subduction in the north is deformed by the strong pushing from the south, and the force from the north is much weaker. The subduction is made up by the old high density crystalline basement from the Tarim basin and the Junggar basin. The thickening is also expressed by the thickness of crust measuring 65-70km under the main body of Tian Shan and 40-45km under the two basins. The major faults in the area appear to be steep through the crust, and those outreaching to the low velocity bodies are believed to associate closely with the mantle material and earthquake activity.