Provenance analysis of Cretaceous peripheral foreland basin in central Tibet: Implications to precise timing on the initial Lhasa-Qiangtang collision

Abstract

Mesozoic strata along northern margin of the Lhasa terrane near Dingqing, Tibet provide a semi-continuous record of the Bangong-Nujiang Ocean closure and the subsequent Lhasa-Qiangtang collision. In this study, we present results of sandstone petrographic, detrital zircon UPb, and Cr-spinel geochemical data to determine the provenance of the Mesozoic strata (from the Triassic Quehala Group and the Mid-Jurassic to Lower Cretaceous Xihu, Lagongtang, and Duoni Formations, which are young from ~220 Ma to ~100 Ma) in this region, thereby allowing for interpretation of their tectonic setting. The similar 1200–900 age cluster from the lower Xihu Formation to that of the Triassic Quehala Group and the distinct age peaks at ~200 Ma and ~146 Ma from the upper Xihu Formation suggest a Lhasa terrane provenance to the south. Distinctive age clusters of 300–210 Ma and ~1800 Ma and Cr-spinel composition analysis of the Lagongtang Formation indicate a provenance shift from the Lhasa terrane to the Qiangtang terrane and the Bangong-Nujiang suture zone to the north. The Lagongtang Formation was deposited in a bathyal-abyssal to shallow-slope environment from north to south, that we interpret as the foredeep depozone and distal foredeep of a peripheral foreland basin system that developed due to flexural subsidence related to the Lhasa-Qiangtang collision and terrane accretion. The age of the Lhasa-Qiangtang collision is constrained by a ~140 Ma tuffite UPb age at the base of the foreland basin strata. An angular unconformity between the Xihu and Lagongtang Formation, which we interpret as the result of the Lhasa-Qiangtang collision. Our results indicate that the Lhasa-Qiangtang collision initiated around ~140 Ma in the Dingqing region, simultaneously with previous determinations 1200 km to the west near Gaize area. Therefore, we prefer quasi-simultaneous onset of collision along-strike to zippering collision models wherein the east collision age is older than the west.