Provenance of the Early Triassic in the southwestern Sichuan Basin, Upper Yangtze, and its implications for tectonic evolution

摘要

The opening and closure of the Paleo-Tethys Ocean and the tectonomagmatic thermal event in the Emeishan Large Igneous Province (ELIP) along the western margin of the Yangtze Block during the late Paleozoic to early Mesozoic shaped the unique pattern of the basin–mountain system. To put constraints on the provenance and tectonic settings of the Early Triassic deposition in southwestern Sichuan, the detrital compositions and major and trace elements of clastic rocks from the E’mei and Meigu sections were analyzed. The detrital components of sandstones in southwestern Sichuan are related to basaltic, short-transport, recycled clastics. Detrital zircons from the bottom of the Feixianguan Formation in the Meigu section yield U–Pb ages ranging from 246 to 280 Ma, with a major peak at ～258 Ma, which are consistent with those of published data from the ELIP major magmatic event. The geochemical characteristics of sandstone are similar to the high-Ti Emeishan basalt of the ELIP and Precambrian to Permian sedimentary rocks of the Yangtze Craton. These results, combined with the research findings based on paleogeography data, indicate that the Early Triassic strata in the E’mei–Meigu region probably originated from both the ELIP and Khamdian Paleoland of the inner Yangtze Craton. The formation of the Sichuan Basin was mainly controlled by the Khamdian Paleoland during that time.