Provenance of Silurian sandstones in the South Kunlun terrane, West Kunlun (NW China) and the timing of the closure of the early Paleozoic Kudi-Qimanyute Ocean

Abstract

The West Kunlun Orogenic Belt (WKOB) records the early Palaeozoic subduction and accretion events related to the Proto-Tethys Ocean along the southwestern margin of the Tarim Block. The branch of the Proto-Tethys Ocean in the West Kunlun region is known as the Kudi-Qimanyute Ocean, whose consumption and closure have resulted in the collision between the North Kunlun terrane (NKT) and the South Kunlun terrane (SKT). However, the age and process of ocean closure have been widely debated. In this study, we present new U-Pb ages and Hf isotope data of detrital zircon and monazite from the Silurian sandstones at the northern margin of the SKT, which reveals a significant shift of sedimentary provenance, indicative of the transition in tectonic setting from a continental forearc to a collisional foreland basin. Provenance analysis indicates that detrital zircon age spectrum from the lower part of the sampled section shows an unimodal pattern and is dominated by early Paleozoic zircon grains derived from the SKT and the Tianshuihai Terrane (TSHT) magmatic arcs. In contrast, the ages of detrital zircons from the sample in the middle part of the section range from Neoproterozoic to Archean with prominent peaks at around 1.1 Ga, 1.4 Ga, and 1.6–1.8 Ga, which are interpreted to be recycled from older (meta)sedimentary rocks in the SKT and TSHT. This change reflects the burial of the magmatic arc beneath a prograding wedge of detritus, sourced from the advancing TSHT and SKT, as a result of the continental collision. Based on the depositional age of the Qaite Formation constrained by the youngest detrital monazite, as well as post-orogenic magmatism and sedimentary records in the region, the closure of the Kudi-Qimanyute Ocean can be constrained to the middle-late Silurian period (427–420 Ma). The detritus in the upper part of the section consists of varying amounts of early Paleozoic and Precambrian grains. The reappearance of late Neoproterozoic to early Paleozoic components is attributed to the re-exposure of the early arc rocks in the SKT and the TSHT during the collisional process. The abundant Archean to Mesoproterozoic detritus in the studied samples reflects the age and composition of the Precambrian basement of the SKT and TSHT. A comprehensive comparison of Precambrian detrital zircon U-Pb and Hf isotopic data indicates that SKT and TSHT share a basement affinity with Western Laurentia, suggesting they were likely part of Western Laurentia within the Rodinian supercontinent.