Provenance and tectonic uplift of the Upper Triassic strata in the southern Songpan-Ganzi fold belt, SW China: Evidence from detrital zircon geochronology and Hf isotope

Detrital zircon geochronology can not only help to determine the maximum depositional ages of sedimentary strata but also provide key constraints on the sediment provenance. The provenance of the Late Triassic flysch in the Songpan-Ganzi fold belt, SW China and the uplift history possibly occurred at slightly later remain debated. This paper reports new detrital zircon U-Pb ages and Hf isotopic data of five sandstone samples from the Upper Triassic Zhuwo, Xinduqiao, Lianghekou, and Yajiang formations ( upward in section) in Yajiang, southern Songpan-Ganzi fold belt. The youngest detrital zircon ages indicate that the deposition of Zhuwo and Xinduqiao formations initiated around 229 Ma and 223 Ma, respectively. The probability density plots show that these four formations collectively yield age peaks of Middle Ordovician to Early Devonian ( ca. 465 398 Ma) and Middle Permian to Late Triassic ( ca. 271 225Ma). Except for one sample from the Lianghekou Formation, the other samples have age peaks of Paleoproterozoic ( ca. 1. 90 1. 86Ga) and Neoproterozoic ( ca. 872 712Ma). The Hf isotopic data indicates that younger than 300Ma grains are mainly sourced from the Emeishan large igneous province to the east and the Yidun magmatic arc to the west. Our provenance study reveals that the Late Triassic sediments in the southern part of the Songpan-Ganzi fold belt is probably derived from the South China Block and the Yidun Terrane. This paper proposes that, during the Late Triassic, the Songpan-Ganzi fold belt may have experienced rapid uplift and exhumation within 18Myr due to the strong convergence of surrounding terranes, following by the sediment delivery to the western margin of the Sichuan Basin.