Stratigraphic Record Of The Upper Permian Xuanwei Formation About The Tectonic Activity In Emeishan Large Igneous Province

There is a massive magma eruption event in the Southwest China,which happened on Middle-Late Permian,and the spewing lava widely distributes in Yunnan,Sichuan and Guizhou provinces,which formed a large igneous province recognized by the international earth science academia,and it affects changes of sea and land,sedimentary characteristics,and so on,so many international and domestic scholars pay attention to it.This article mainly discusses the sedimentary response of surface after the eruption of the Emeishan basalt.The article emphatically expounds the source of sediment of the Upper Permian Xuanwei Formation in Emeishan Large Igneous Province,and the control action of the fault zones on sedimentary characteristics in the studied area.Besides,the article analyzes the sea level change of Late Permian,and has detrital zircon LA-ICP-MS U-Pb chronology study in the lower strata of Xuanwei Formation.Through the field investigation in the Upper Permian sedimentary strata,the author finds that the West Sichuan Central Yunnan oldland uplifts in the Late Permian,and the distribution of Xuanwei Formation is around the oldland,and from west to east the lithofacies evolution is from the continental facies sedimentation to marine facies sedimentation.From Qinghe-Chenghai fracture zone to west and from Ganluo-Xiaojiang fracture zone to east,the Xuanwei Formation thickness trends thickening gradually.Through the sediment provenance of Xuanwei Formation using the method of clastic rocks analysis and sedimentary method,the article concludes that the sediment provenance is the West Sichuan Central Yunnan oldland between Qinghe-Chenghai fracture zone and Ganluo-Xiaojiang fracture zone.The detrital zircon LA-ICP-MS U-Pb chronology study of the sandstone sample in the lower strata of Xuanwei Formation shows that the most of zircons are magmatogenic zircons,a part of zircons experience hydrothermal alteration transformation.The crystal habit of most grains are euhedral-subhedral crystal,and the zircons have poor sorting and psephicity,showing that they are proximal denudation sedimentation.Through analysis,it further explains the provenance may be the oldland.In the study area,there is autochthonous glauconite in the sandstone in the Upper Permian formation.Autochthonous glauconite has significance of facies-indication,and it is often thought to be the role of transgression.In the Late Permian,the coal-accumulation belt migrates from east to west over time,which shows the earth's crust sinks and seawater gradually invades from east to west,thus this indicates there is thermal subsidence after the Emeishan basalt eruption.There is obvious difference on sea level change between Yangtze platform and the global earth,and the phenomenon provides the evidence to support that there is thermal subsidence after the Emeishan basalt eruption.