Evidence of detrital spinel geochemistry for depositional response to the Paleo-Tethyan closure recorded in the Songpan-Ganzi Terrane, eastern Tibetan Plateau

Abstract

The Late Triassic evolution of the Songpan-Ganzi Terrane in the eastern Tibetan Plateau is crucial for understanding the closure of the eastern Paleo-Tethys Ocean. However, the strong thickening and deformation of sedimentary cover make the Songpan-Ganzi geological records complicated and even obscured, impeding the reconstruction of regional tectonic evolution. In this study, we provide new geochemical data of detrital spinels from the Upper Triassic strata in the eastern Songpan-Ganzi Terrane to reveal the provenance and the regional tectonic events involved in the eastern Paleo-Tethyan closure. Results show that detrital spinels from the Upper Triassic Xinduqiao, Zhuwo, and Zagunao formations have variable concentrations of Cr2O3 (24.36–68.56 wt%), Al2O3 (0.13–39.17 wt%), MgO (0.20–21.25 wt%), FeOT (11.15–48.49 wt%), and TiO2 (0.00–4.66 wt%). They are geochemically similar to spinels from both ophiolites and stratiform intrusions, and affinitive to the counterparts from island-arc, supra-subduction zone, or mid-ocean ridge settings. Based on comparison with the spinel compositions from adjacent tectonic zones and in combination with previously published evidence from paleogeography, paleocurrent orientation, and geochronology, we propose the detrital spinels from the Upper Triassic sequence in the eastern Songpan-Ganzi Terrane were mainly recycled from the Lower–Middle Triassic strata in the West Qinling Terrane, with minor concentrations derived from the A’nyemaqen ophiolites. This provenance inference presents a new insight into the closure time of the eastern Paleo-Tethys Ocean.