Neogene Source-to-Sink Relations between the Pamir and Tarim Basin: Insights from Stratigraphy, Detrital Zircon Geochronology, and Whole-Rock Geochemistry

Abstract

The Tarim Basin, as the largest inland basin on the planet, provides a valuable opportunity to understand the mountain building of the northern Tibetan Plateau and its effects on basin development. Here we present a synthesis of sedimentology, zircon U-Pb geochronology, and bulk-rock geochemistry of Neogene sediments in the Qimugan section, southwest Tarim Basin. Spatial variation in zircon U-Pb age distributions from early Miocene clasts at Qimugan and Oytag suggest significant dextral strike-slip on the Kashgar-Yecheng transfer system likely commenced during the Oligocene–early Miocene. Over time, age peaks of ∼20 and ∼107 Ma in a middle Miocene sample at Qimugan suggest significant headwater erosion of the ancient Yarkand River reached the southeast Pamir–Karakoram hinterland as it does today. This is coincident with a relatively steady decrease in chemical weathering of source terranes during the middle-late Miocene, suggesting a climate transition from warm and/or humid to cool and/or dry in the Pamir-Karakoram. Under global cooling, middle Miocene changes in both provenance and geochemistry at Qimugan require topographic growth of the Pamir-Karakoram interior at that time, coeval with initial formation of the fold-thrust system and doming of the Muztaghata massif in the eastern Pamir, in addition to a prominent depocenter shift and sediment load in the southwest Tarim Basin. Subsequently, stable sediment provenance and depocenters suggest the current tectonic-sedimentary configuration in the eastern Pamir–southwest Tarim Basin has been established since the middle-late Miocene. These observations can be explained by a model of crustal contraction below the southeast Pamir–Karakoram and strain propagation to the Tarim Basin, possibly related to resumed Indian crust subduction. Our results thus support compressional deformation extended to all margins of the northern Tibetan Plateau by the middle-late Miocene.