Late Cenozoic Deformation Sequence of a Thrust System along the Eastern Margin of Pamir,Northwest China

A thrust belt formed in the basin along the eastern margin of Pamir.The thrust belt is about 50 km wide,extends about 200 km,and includes three compressive structures from south to north:the blind Qipan structural wedge and Qimugen structural wedge,and the exposed Yengisar anticline.The thrust belt displays a right-stepping en echelon pattern.The Qipan structural wedge dies out northward to the west of the Qimugen structural wedge,and the Qimugen structural wedge dies out northward to the west of the Yengisar anticline.Detailed analysis of seismic reflection profiles of the western Tarim Basin reveal that fan-shaped growth strata were deposited in the shallow part of the thrust belt,recording the deformation sequence of the thrust belt.The depth of the Cenozoic growth strata decreases from south to north.The growth strata of the Qipan structural wedge is located in the middle-lower section of the Pliocene Artux Formation(Na),the growth strata of the Qimugen structural wedge is close to the bottom of the Pleistocene Xiyu Formation(Qx),and the growth strata of the Yengisar anticline is located in the middle section of the Xiyu Formation(Qx).Combined with magnetostratigraphic studies in the western Tarim basin,it can be preliminarily inferred that the deformation sequence of the thrust belt along the eastern margin of Pamir is progressively younger northward.The geometry and kinematic evolution of the thrust belt in the eastern margin of Pamir can be compared with previous analogue modeling experiments of transpressional deformation,suggesting that the thrust belt was formed in a transpressional tectonic setting.