DYNAMIC SYSTEM AND KINEMATICS MODEL OF CENOZOIC STRUCTURAL DEFORMATION IN QAIDAM BASIN AND THE NORTHERN TIBETAN PLATEAU

Cenozoic foreland deformation in Qaidam basin was constrained by two boundary conditions: the narrow extension of basin in south-north direction and the resistance of Altyn Tagh fault. These two boundary conditions disabled the development of stable foreland area and wedge sedimentary structure in Qaidam basin. Results of surface wave imaging from ambient noise across Qaidam basin and the northern Tibetan plateau indicate that the middle-lower crust is significantly deflected southward and westward by tectonic loading, which implies the northward thrusting from the eastern Kunlun orogenic belt may be dominant in Cenozoic deformation. Moreover, a series of arched mountains between the eastern Kunlun and Qimantage orogenic belts imply a unique Cenozoic dynamic system, in which once straight eastern Kunlun strike-slip faults were gradually pushed northward into arch shapes and die young, but the newborn strike-slip fault still maintained its straight shape with east-west direction. It is also indicated from seismic interpretation that structural shortening in Qaidam basin since Pliocene was mainly concentrated in the area between Qimantage mountain in southwestern Qaidam and Saishiten – Luliang mountains in the northern Qaidam, and gradually decreased toward the eastern Qaidam. Based on the statistics of over 600 earthquake events greater than 3 Mb, the focal depths in the southwestern Qaidam are mainly in the range of 12 – 13 km, which reveal the possible existence of an active detachment in basin basement at this depth. This active detachment corresponds to the time of 6s – 7s in seismic section and elevates northward gradually, which led to stratified structural deformations in the overlying Cenozoic cap rock, forming a huge thrust system composed of the piedmont fault terrace zone, Yingxiongling duplex structural zone and the northwestern Qaidam imbricate structural zone from south to north. Its front might have extended to the northern margin of Qaidam basin. Therefore, we deem that the Lenghu and Eboliang shallow anticlines in the northern Qaidam belong to the southwestern Qaidam thrust system, while the Lenghu and Eboliang deep anticlines belong to the northern Qaidam thrust system, these two foreland thrust systems were imbricated each other and characterized by “obduction” and “subduction” respectively.