Deep Structure And Orogenic Mechanism Of The East Kunlun Mountains From Teleseismic Receiver Function

East Kunlun Mountains is located in the northern part of the Qinghai-Tibetan Plateau and is an important area for studying the northward growth of the plateau.The Cenozoic structure in this region is complex and seismicity is widely developed.It is a natural site for studying issues such as structural deformation under the background of the uplift of the Qinghai-Tibetan Plateau.Using the teleseismic events recorded by 121 broadband seismic stations deployed by the INDEPTH IV project in middle-northern Tibet during 2007 and 2009,we selected 359 teleseismic events and obtained the crust-mantle structure and Vp/Vs ratio in the study area,through the receiver function CCP imaging and the improved H-k stacking method,as well as multi-parameter and multi-method comprehensive verification and analysis.Combining the results of other geophysical observations and this research,this paper analyses the deep structure and orogenic process of the East Kunlun Mountains,attempting to deepen the uplift mechanism and deep dynamic process of the Mountains.The research progress and preliminary understandings are summarized as follows:(1)There is a "double Moho" structure ?30-90 km north of the Muztagh-Kunlun-Anyimaqen Suture.The upper Qaidam Moho(?45-50km)gradually shallows and weakens southwards,and the lower Kunlun Moho extends from a depth of ?65km down to a depth of ?90km in the upper mantle of Qaidam.A parallel negative conversion occurs on the north-dipping positive converter,indicating a low-velocity zone between them.(2)The velocity ratios are abnormally high beneath the middle of the Qiangtang terrane and the northern part of the Hoh Xil terrane(average Vp/Vs?1.83).The ratios are also higher than global average beneath the East Kunlun Mountains.This indicates that partial molten materials are widely distributed in the middle-lower crust of northern Tibet.(3)The CCP stacking image of the mantle transition zone crossing the central and eastern part of the East Kunlun Mountains shows that the thickness of the mantle transition zone in northern Tibet is almost the same as the global average.The depth of the 410 km and 660 km discontinuities in the middle is ?10km lower than that in the east.This indicates that there is no large temperature anomaly in the mantle transition zone in northern Tibet and the average shear velocity above 410 km depth is lower than global average in the middle part of the northern Tibet.The continuous geometry of the 410 km and 660 km discontinuities in northern Tibet indicates that the Indian lithosphere in northern Tibet has not subducted to the depth of the mantle transition zone.(4)According to the characteristics of the "double Moho" of the East Kunlun-Qaidam junction and the higher Vp/Vs ratio in northern Tibet,this paper put forward a new proposal that the orogeny of the East Kunlun Mountains is related to the intrusion of its middle crust into the lower crust of Qaidam,as well as the underthrust of its lower curst into the Qaidam upper mantle.