Oblique strike-slip superimposed structure in Yingxiong range, western Qaidam basin and its response to Altyn Tagh fault and Eastern Kunlun fault

The Yingxiong Range is the largest anticlinal belt within the triangular overlapping zone between the Altyn Tagh Fault and the Eastern Kunlun Fault and thus records the critical information concerning the strike-slip superimposition between the two large-scale left-slip faults. The detailed structural analysis on the basis of 3D seismic data shows that the Shizigou (SZG) and Youshashan (YSS) structures in the Yingxiong Range are controlled by NE-dipping low-angle thrust faults at shallow depth and three groups of faults including the NW-striking inverted faults, the WNWstriking XI fault and the N-S-striking Shidong fault zone at deep levels. The inverted faults were right-stepping en-echelon sinistral transtensional normal faults in the Eocene. Fracture analysis on cores of the U. Xiaganchaigou Formation shows the existence of syn-sedimentary normal faults which indicate Eocene extension deformation in the Yingxiong Range. The Eocene transtensional normal faults constituted a half-graben structural system and controlled the formation of the SZG sag. In the early Miocene, the XI fault obliquely superimposed the pre-existing Eocene transtensional normal faults, causing the reactivation of these faults in a reverse sense. Simultaneously, the Shidong fault zone started to develop as a dextral tear fault. The oblique strike-slip superimposition from transtension to transpression in the Yingxiong Range reflects the differential controlling effects of the asynchronous initiation of the Altyn Tagh Fault and the Eastern Kunlun Fault on the structural evolution and oil-gas reservoir development in the western Qaidam Basin.