Late Cenozoic Structural Framework And Evolution Along The Eastern Margin Of The Pamir Salient, Northwestern China

Based on seismic reflection profiles, surface geological survey and oil well data, this paper studies late Cenozoic structural framework and evolution along the eastern margin of the Pamir Salient.This paper constrains structure of the Wuyitake-Momoke transfer system (WMTS). To the east of the WMTS, several balanced cross sections are constructed to study geometry and kinematic in the basin-range junction belt of the West Kunlun Shan-Southwestern Tarim basin. Using the vertical projection method of the axial surface mapping, this paper constructs the blind faults and structural framework of the West Kunlun Shan-Southwestern Tarim basin. Moreover, this paper try to constrain basin deformation time based on growth strata shown in the seismic sections, and investigate the Cenozoic structural evolution along the eastern margin of the Pamir Salient.Structural framework along the eastern margin of the Pamir Salient can be summarized as coexistence of the outcropped WMTS and the blind compressive structural belt, either of them developed independently.The north-northwest-striking WMTS exposes in the piedmont of the West Kunlun Shan, and extends about 300km from Momoke to Wuyitake. The sinistral en echelon WMTS includes several steep right-dextral faults:Qipan Fault, Aertashi Fault, Kumtag Fault, Kusilaf Fault, Yarkand Fault. These faults comprises complex network of anastomosing faults is about 50km wide across strike and could fully accommodate late Cenozoic significant northward translation of the Pamir salient with respect to the Tarim basin. The WMTS was active between Miocene and Pliocene. Fault geometry indicates that the direction of maximum horizontal stress is south-north and in agreement with regional stress field.The seismic profiles adjacent to the WMTS reveals that blind compressive structures developed along the western Tarim basin. The compressive structural belt is about 15-40km wide and extends about 200km from Momoke to Wuyitake. The belt includes three compressive structures from south to north:Qipan structural wedge, Qimugen structural wedge, Yengisar anticline, of which the direction of maximum horizontal stress are 60° NE,40° NE,15° NE, respectively. Therefore, the direction of maximum horizontal stress is different from south-north regional stress field.The compressive structural belt deformed since Pliocene. The growth strata of the Qipan structural wedge locates in the bottom of the Aertashi Formation (N2a), the growth strata of the Qimugen structural wedge locates in the bottom of the Xiyu Formation (Q1x), the growth strata of the Yengisar anticline locates in middle Xiyu Formation (Q1x). The growth strata documents that these three compressive structures deformed since 5Ma,3-4Ma, and 1-2Ma, respectively.The research results supports a kinematic model along the eastern margin of the Pamir salient since late Cenozoic:14-5Ma, WMTS dextrual strike-slip; 5-3Ma, compressive structural wedges; 2Ma-Present, WMTS extends northward.