The collision‐related structures revealed in the northern Tarim Basin and their geological significance

Abstract

The South Tianshan on the southern margin of the Central Asian Orogenic Belt (CAOB) is a collisional orogenic belt between the Tarim continent and Ili‐Central Tianshan volcanic arc. The initial time of the collision remains debated, with proposed timing from Early Devonian to Middle Triassic. Almost all the previous studies on this collision were carried out within the South Tianshan Mountains, few within the related basins. End Permian–Triassic thrusts and Jurassic–Cretaceous normal faults were discovered in the northern Tarim Basin where is the southern piedmont of the South Tianshan Mountains after careful and systematic seismic interpretation. The end Permian–Triassic thrusts are constituted by both basement‐involved and thin‐skinned thrusts. They are likely seen as the syn‐collision compressional structures of the South Tianshan collisional orogen. The syn‐collision thrusts constitute the main faults in the study area. Consistent with the Triassic/Permian and Jurassic/Triassic unconformities, two thrusting phases occurred, at end Permian–beginning Triassic and end Triassic–beginning Jurassic, respectively. The Jurassic–Cretaceous normal faults usually arrange into stair‐step or graben‐horst structures in profile and en echelon normal fault zones horizontally. They are attributed as the results of the regional extensional stage in the CAOB. This regional extension stage provides a good constraint for the ending time of the collision between Tarim and Ili‐Central Tianshan blocks. The normal faulting time is revealed by normal fault growth indexes. According to these observed syn‐collision compressional and subsequent extension structures, it can be fairly inferred that the collision between Tarim and Ili‐Central Tianshan was initiated at end Permian, lasted through the Triassic and ceased at end Triassic, and then evolved into the Jurassic–Cretaceous extensional tectonic stage.