Arcuate Pamir in the Paleogene? Insights from a review of stratigraphy and sedimentology of the basin fills in the foreland of NE Chinese Pamir, western Tarim Basin

The tectonic evolution of the Pamir bears essential information for understanding intracontinental tectonic processes within the context of India-Asia convergence. However, it is unclear whether the arcuate shape of the Pamir is entirely the result of the India-Asia collision, or may have been in part an inherited, pre-Cenozoic feature. In this study, we address the evolution of the NE Chinese Pamir during the Paleogene by reviewing the stratigraphy of twelve sections in the western Tarim Basin and the establishment of sedimentary facies. The results indicate three episodes of deposition of alluvial coarse sediments in the foreland regions of NE Chinese Pamir during the (1) early Paleocene, (2) late Paleocene to early Eocene and (3) middle Eocene to Oligocene, respectively. These are correspondingly attributed to (1) retroarc deformation in an Andean-type margin of the southern Asia during subduction of the Neo-Tethys Ocean, (2) the immediate response in the Pamir to the India-Asia collision, and (3) continued India-Asia convergence. The alluvial conglomerates with grain-size up to 5-10 cm, imply a transport distance <60 km from the fan apex. This result, together with the 20-50 km northward thrust displacements, suggests that the orogen/basin boundary between the Pamir and the Tarim-Alai Basin was located less than ca. 80-110 km to the south from the present location of the Main Pamir Thrust during the Paleogene, indicating the arcuate shape of the Pamir was already largely established by the Paleogene, rather than entirely a result of the India-Asia continental collision.