Cenozoic Kinematic History of the Lintan-Minxian-Tanchang Fault in Western Qinling and Its Dynamic Process

The Lintan-Minxian-Tangchang Fault (abbreviation as LMTF) is one of main boundary faults in the hinterland of Western Qinling, which is located at the northeastern margin of the Qinghai-Tibet plateau. It consists of several nearly parallel thrusting-strike slipping faults. Taking the typical section of Pu-Ma fault (F3) of the LMTF as the studying object, the detailed investigation has been carried out for the types and zoning of fault rocks, geometry-kinematics characteristics of various structural elements. The results indicated that F3 fault is mainly a typical shallow level brittle fault, which experienced at least three phase deformation with different geometric-kinematic characteristics since the Cenozoic era. The first phase deformation is characterized by high angle thrusting from north to south, with NNE steep dipping (dip angle around 70°~80°); the second by medium angle thrusting from north to south, with NNE medium dipping (dip angle around 30°~50°); and the third by sinistral strike-slipping, with NW trending and SW dipping (dip angle around 60°~70°). Based upon comprehensive analysis for the involved strata ages, structural cutting relationship in the fault zone, the regional fault activities, sedimentary basin evolution and crustal uplifting in northeast margin of Qinghai-Tibet plateau since Cenozoic era, it is suggested that the first period high angle thrusting was occurred at beginning of middle Eocene (40~50 Ma), which maybe continued to beginning of Oligocene; the second period medium angle thrusting was occurred at end of Miocene or beginning of Pliocene, which maybe continued to early Quaternary; and the third period sinistral strike-slipping was just the tectonic event occurred since late Quaternary. Three period fault activities of F3 fault in LMTF mentioned above maybe documented the remote tectonic responses of the West Qinling to the three different evolution stages during the collisional converge between India and Eurasian plates. First period high angle thrusting could be related to the compression shortening during India-Eurasia peak collision (55~45 Ma); the second period medium angle thrusting was stood for the out-spreading of crustal thickening and uplifting of Qinghai-Tibet plateau; the third period sinistral strike-slipping was obviously lagged to E-W extension and NW trending strike-slipping, which may indicate the unsynchronized uplifting and strike-slipping in the northeastern margin of Qinghai-Tibet plateau and the hinterland of Qinghai-Tibet plateau. These results may reflect that the present entire Tibetan plateau has been forming by the gradual propagation to the northeast.