The Timing Of The Emeishan Flood Basalt Eruption And Link With The Permian Mass Extinctions

The volcanic eruptions in the Emeishan large igneous province (ELIP) have been commonly considered to be a causal link with end-Guadalupian mass extinction event, whereas the largest Permo-Triassic boundary (P-TB) mass extinction during geological history have been attributed to volcanic activity in the Siberian large igneous province. However, recently we found a well-preserved section composed of several layers of tuffaceous rocks interbeded with the basaltic lavas at the eastern part of the ELIP that provides a rare opportunity to directly monitor cause of the mass extinction. Based on the studies of detailed field geology, petrology, stratigraphy, palynology, geochemistry and zircon geochronology and Hf isotope and trace element, we have acquired the following results:(1) after a detailed geological measurement and drilling catalog, we identified five volcanic stages in this section and the thickness of lava and tuff in each volcanic stage accounted for lava and tuff thickness of the entire section from bottom to top are 4% and 6%,74% and 12%,13% and 17%,4% and 32% and 5%- and 33%, respectively; (2) geological field observations and petrographic studies show that the early and late volcanic activity in this study area occurred in shallow sea and continental environment, coincidence with the -260Ma and-252Ma regional palogeography; (3) the results of five LA-ICP-MS zircon dating show that the ELIP volcanic eruptions in this area appear two distinct volcanic stages of the earlier ～260-258Ma and later ～253-251Ma, and the palogeographic study supports the zircon dating data; furthermore, zircon Lu-Hf isotope results show that the two volcanic activity are associated possibly with Emeishan mantle plume; (4) we find several combusted wood or charcoal fragments based examination of from volcanic rock in the later volcanic stage (-253Ma-251Ma), which are identical with charcoal or soot layer at the P-T boundary in the South China; it indirectly confirms that our dating results are reliable and correct. In summary, we have made the following views:the ELIP volcanic eruptions in this region appear two significant volcanic stage:a-260-258Ma large-scale volcanic eruption occurred in shallow sea environment (the proportion of lava is a-87% of the entire volcanism) with a short duration (< 3Ma); may be related to the end-Guadalupian extinction; a smaller continental volcanic eruption occurred during the -253-251Ma with a large proportion of tuffs (accounting for 65% of the thickness from the entire section), which has a causal relation to the end-Permian mass extinction. The widely distributed charcoal or soot layers at the P-T boundary in the South China may be attributed to the later Emeishan volcanism (-253-251Ma).