Origin of the Songpan-Garze terrane, Tibetan Plateau: A perspective from the tectonic evolution of the Palaeo-Tethys Ocean

Abstract The Songpan-Garze terrane is the largest Triassic remnant flysch basin on Earth that formed as the Palaeo-Tethys Ocean closed during the final amalgamation of the Pangaea supercontinent. However, the origin of the Songpan-Garze terrane is highly controversial. A synthesis of the tectonic evolution of the Palaeo-Tethys Ocean and its branches surrounding the Songpan-Garze terrane is presented, which clarifies the nature and relationships among the many Palaeo-Tethys sutures. Provenance analyses suggest that branches of the Palaeo-Tethys near the Songpan-Garze terrane closed before the Early Triassic. In contrast, the main Palaeo-Tethys Ocean (Longmu Co-Shuanghu) did not close until the early Late Triassic. This study argues against the Songpan-Garze terrane being a remnant ocean basin, and proposes that it was a back-arc basin of the main Palaeo-Tethys Ocean. It initially underwent extension by the combined effects of the main Palaeo-Tethys Ocean subduction and the Emeishan mantle plume in the Late Permian, and subsequently developed into a back-arc basin in the Triassic to deposit huge turbidites derived from all surrounding terranes or orogens. The final closure of the main Palaeo-Tethys Ocean in the early Late Triassic and subsequent continent-continent collision led to basin inversion in the Late Triassic. Supplementary material at https://doi.org/10.6084/m9.figshare.c.6751582