Genesis of end-Guadalupian bauxite and pyrite deposits in the Youjiang Basin (South China): Insights into the causative link between magmatic events and mass extinction

Mass extinction was commonly considered as the response to interaction between geosystems, and volcanism can be viewed as a vital link between the surface systems and deep geodynamic processes. This causative link between end-Guadalupian mass extinction and volcanism has been clarified, based on the research of bauxite and pyrite deposits in the Youjiang Basin, South China Block (SCB). Geochronological and geochemical evidences show that the source materials of bauxite-pyrite deposits were mainly derived from the Emeishan large igneous province (LIP) to the northwest and the continental arc along the SW margin of SCB associated with the subduction of the Paleo-Tethys Ocean underneath the Indochina block. Volcanic ash fallout by atmospheric dispersal driven by the easterly trade winds could best account for the spatial variation of both bauxite and pyrite deposits given their relative paleogeographic positions with respect to the two flanking sources. Massive volcanic tephra from arc volcanism fell on exposed carbonate platforms, underwent intensive chemical weathering and transformed into bauxites under the warm and humid tropical climate in Tethys, which could be also favored by acid precipitation caused by volcanic degassing. Extensive SO2 released from Emeishan LIP emission could be the major source of pyrite ores, probably with minor contribution from arc volcanism. This indicates that the prolonged and extensive continental arc volcanism induced environmental stress in the poorly-ventilated PaleoTethys Ocean, while the coincidental eruption of the large igneous provinces was the final straw, leading to the dramatic biotic crises during the Middle-Late Permian interval.