Devonian-Triassic Clastic Provenance Evolution And Tectonic Significance In Dian-Qian-Gui Basin

Dian-Qian-Gui basin is one of the famous Carlin type gold deposits in the world.A systematic understanding of the source of clastic materials in the Devonian-Triassic strata in this area can provide new data for the follow-up exploration and scientific research.This study is the first time to combine the U-Pb geochronological analysis method of zircon and monazite to analyze and test the monazite from Devonian Posongchong formation and the zircon from Triassic luolou formation in Dian-Qian-Gui basin.The results show that most zircons have magmatic zones with Th/U values > 0.4.The U-Pb ages of zircons are concentrated in 308-396 Ma,440-680 Ma,727-930 Ma,1004-1266 Ma,1400-1880 Ma and 2360-2724 Ma.U-Pb detrital monazite geochronology yields dominant Pan-African(657-460Ma)and minor early Neoproterozoic(998-798Ma)contents.By comparing the age distribution characteristics of detrital zircons and monazites between the study area and the surrounding blocks,and combining the lithofacies palaeogeography,palaeo-ocean current and palaeo-current,the comprehensive analysis shows that the provenance of the study area is mainly from the northern edge of East Gondwana(Northern India,Himalaya,Lhasa,Qiangtang terrane,Hainan Island,and Western Australia),with the Jiangnan orogen also providing some clastic materials.The Carboniferous Permian clastic materials in Dian-Qian-Gui basin are mainly from Emeishan Large Igneous Province,and the Triassic clastic materials in Dian-Qian-Gui basin are mainly from the North Vietnam block,the tectonic mountain system of Hunan,Guangdong and Guangxi and Yunkai area.Based on the identification of Devonian clastic materials from the northern edge of the East Gondwana in Dian-Qian-Gui basin,and combined with previous research results,it is considered that the South China block was located in the northern edge of the East Gondwana in the early Paleozoic and was a part of the Gondwana continent.In addition,the Triassic clastic material source of Dian-Qian-Gui basin comes from the North Vietnam block,which proves that the Paleo-Tethyan Ocean closed gradually during the Indosinian period,and the South China block collided with the Indosinian block along the Songma suture zone.