Provenance of Lower Cretaceous sedimentary rocks in the northern margin of the Lhasa terrane, Tibet: Implications for the timing of the Lhasa-Qiangtang collision

Abstract

Placing precise constraints on the timing of initial Lhasa-Qiangtang collision is essential to understand the assembly processes and uplift mechanism of the Tibetan Plateau prior to the Cenozoic India-Asia collision. Along the over 2000-km-long Bangong-Nujiang suture zone, the timing of initial Lhasa-Qiangtang collision remains highly controversial, with estimates ranging from Middle Jurassic to Late Cretaceous, spanning nearly 100 Myr. Provenance analysis of clastic rocks has been proved as an effective approach to pinpoint the timing of initial continental collision by documenting the provenance exchange from one plate to another. This study focuses on the Lower Cretaceous Duoni Formation in the Gerze area of northern Lhasa margin. The youngest detrital zircon U-Pb ages along with other age constraints in literature indicate that the Duoni Formation was deposited during the late Early Cretaceous (119–122.7 Ma). A combined sandstone petrographic, detrital zircon and Cr-spinel provenance analysis demonstrates that the Duoni Formation records unambiguously suture zone- and Qiangtang-derived detritus from the north, such as the Bangong-Nujiang ophiolites and southern Qiangtang arc. Based on structural geology, stratigraphy and provenance analysis, the Lower Cretaceous Duoni Formation on the northern Lhasa margin was most likely deposited in a peripheral foreland basin in response to the Lhasa-Qiangtang collision. These data provide undisputable evidence that the Lhasa-Qiangtang collision was well underway and the Lhasa terrane had been welded to the southern margin of Eurasia by at least the late Early Cretaceous (119–122.7 Ma).