Abstract

The Hoh Xil Basin in the central Tibetan Plateau was the locus of thick accumulation of terrestrial sediments from the Late Cretaceous to Neogene, providing an archive of regional tectonic activity both before and after initiation of the early Paleogene India-Asia collision. This work focuses on the stratigraphy and provenance of the poorly studied western part of the Hoh Xil Basin. Lithostratigraphy, carbonate oxygen isotopic composition, and deformation features suggest that the braided river and alluvial-fan that dominated the Kangtuo Formation in the southern West Hoh Xil subbasin can be correlated with the Late Cretaceous–early Eocene Fenghuoshan Group deposits of the East Hoh Xil subbasin, whereas deltaic, shallow lacustrine, and evaporite strata of the Suonahu Formation in the central-northern West Hoh Xil subbasin can be correlated to the middle Eocene–early Oligocene Yaxicuo Formation of the East Hoh Xil subbasin. These observations suggest that the eastern and western parts of Hoh Xil Basin evolved as a unified basin during Late Cretaceous–Oligocene time. Detrital zircon U-Pb ages indicate that the Kangtuo Formation and Fenghuoshan Group mainly received detritus from the Qiangtang terrane to the south, whereas the age probability distributions of the Suonahu Formation and Yaxicuo Formation sandstones are more similar to zircon ages reported for the northern Qiangtang terrane and within the Hoh Xil terrane. We favor a tectonic model with Late Cretaceous–early Eocene contractional deformation and topographic growth of the south-central Qiangtang terrane that caused flexural subsidence of the south-central Hoh Xil region within a retroarc foreland basin, relative to the Tanggula thrusts in central Qiangtang. Following the onset of India-Asia collision, the locus of contractional deformation moved northward, marked by activity of the Fenghuoshan and Hoh Xil thrust systems within the Hoh Xil region, and resulting in transformation of the Hoh Xil foreland basin to a hinterland basin. We suggest that both middle Eocene to late Oligocene upper-crustal shortening and associated thickening of the lower crust and mantle lithosphere as well as late Oligocene to Miocene loss of dense mantle lithosphere contributed to the topographic growth of the Hoh Xil Basin.

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