Transverse structure and model of fault slivers in the northern part of the Tarim block

Abstract：The shallow tectonic system in the northern Tarim basin adjacent to the southwestern Tianshan Mountains consists of the Kashi depression, Kalpin Tagh thrust nappe tectonic belt and Kuqa foreland depression thrust belt, which are distributed in the form of 1－3 rows parallel to the orogenic belt in the mountain front. It is also a thrust nappe system composed of the basal detachment fault flat and fault ramp, showing distinct E-W-directed transverse segmentation. The deep tectonic system is marked by a set of NW-trending faults, which divide the area into four fault slivers. The authors systematically study the deep transverse tectonic system in the area in the contexts of the structural layers, gravity and aeromagnetic anomalies and density of earthquake occurrences and recognize the depths of detachment surfaces of the lithospheric layers by using the statistical results of the depth and frequency of the earthquakes. On that basis, the authors discuss the regional NW-trending transverse tectonic system in detail. In the paper, the Karayulgun fault belt and Korla fault belt are selected for ｔｈｅ study ｏｆ the transformation relation between the transverse structure and shallow structure and finally a geometric and kinematic model of the fault slivers in the northern part of the Tarim block is proposed, i.e.：the Tarim block is “forced” to be subducted as the NW-directed movement of its deep part is hindered and constrained by the ancient southwestern Tianshan, thus resulting in decoupling of the lithospheric crust, activation of the original transverse tectonic system (NW-trending fault belt) and subduction of the subducting system in the form of fault slivers； in the process of subduction, the detachment of the lithospheric crust and activation of the transverse structure started near the “constraining body” (southwestern Tianshan) and progress toward the interior of the Tarim basin (northern part), and therefore the difference in subduction state between the fault slivers is more obvious and the transverse segmentation is more prominent toward the orogenic belt. It is just because the subduction of the Tarim block in the form of fault slivers that segmentation of the piedmont depression thrust belt (and Tianshan belt) takes place.