Tectonic switch from Triassic contraction to Jurassic-Cretaceous extension in the western margin of the Tarim Basin, Northwest China: New insights into the evolution of the paleo-Tethys Orogenic Belt

Abstract:

The prototype of the Mesozoic basins in the western Tarim Basin and its geodynamics remain controversial. In this contribution, we integrate seismic profiles and borehole data from the Tarim Basin with the analysis of exposed Mesozoic outcrops to provide new insights into tectonic switch from the Triassic contraction to the Jurassic-Cretaceous extension. Seismic profile interpretation and structural balance restoration show that an approximate 60 km wide fold- and- thrust belt were identified from the southwestern edge of the Tarim Basin during the Triassic and strongly overprinted by Late Cenozoic contractional deformation. The Triassic strata were almost absent in the western Tarim Basin and the contineous Jurassic-Cretaceous system unconformably onlapped on the Paleozoic fold and thrust belt. Stratigraphic correlation and distribution show that the Mesozoic successions have a close inheritance in spatial and they were limited in the region of the Triassic fold-thrust belts. Such close spatial-temporal coupling relationship between the Triassic thrust belt and Jurassic-Cretaceous basin indicates that they possibly have a genetic relationship. Thus, we suggest that the important tectonic switch from Triassic contraction to Jurassic-Cretaceous extension in this region could be linked with the evolution of the paleo-Tethys Orogenic Belt. Firstly, during the Triassic period, the western Tarim Basin was involved into an orogeny (possibly the extensive Early Cimmerian collisional orogeny), which may be related to the subduction of the paleo-Tethys Ocean. Secondly, during the Early and Middle Jurassic time, this area were dominant with the post-orogenic extension and a series of nested graben and half-graben basins developed along the fold-thrust belt. During the Late Jurassic-Early Cretaceous, a huge sag basin formed and the former Jurassic rift basin possibly constitute several deep depression centers of this huge basin along the southwestern margin of the Tarim Basin. Subsequently, this region were conformably covered by a thin shallow marine deposits due to the widespread transgression from the Pannonian (Paratethys) Sea in the west during the Late Cretaceous and Paleogene.