Provenance Analysis Of Funing-guichao Basin Of Middle Triassic In Southeast Yunnan

Funing Guichao basin is located in the Yunnan Hainan suture zone between the South China plate and the Indosinian block,bordering Nanpanjiang Basin in the north and Napo basin in the south.Based on the study of the Middle Triassic sediment in Funing Guichao basin,combined with field geological survey and indoor analysis,using heavy mineral data and clastic composition statistics,this paper studies the sedimentary facies,petrological characteristics of sandstone,heavy mineral assemblage characteristics,parent rock types and material sources of the Middle Triassic in Funing Huanchao basin.It is found that the main rock type is lithic greywacke.The detritus is mainly composed of quartz and cuttings,while the cuttings are mainly volcanic and sedimentary.According to the mapping of the clastic composition,the main tectonic environment of the Middle Triassic sandstone in the basin is a cyclonic orogenic belt,and its provenance is related to arc volcanoes.Heavy minerals are mainly sub angular and sub circular,and the main heavy minerals are zircon,pyrite,white titanium,hematite limonite and pyrite.The stable minerals account for the majority,which is characterized by the combination of remote-source transportation and near-source deposition.The main factor analysis and correlation analysis are used to analyze the heavy mineral data of Funing-Guichao basin,so as to determine the type of heavy mineral assemblage in the Middle Triassic sedimentary period,and then to determine the composition of the parent rock and the nature of the provenance area by analyzing the combination characteristics of the heavy minerals.The results show that there are four types of heavy mineral assemblages in Funing Guichao basin in Middle Triassic,which are apatite anatase pyrite,tourmaline monazite ilmenite,zirconalbite garnet and rutile magnetite.The rest of them are some altered minerals.According to the heavy mineral assemblage,the parent rocks are mainly basic rocks,intermediate acid magmatic rocks and metamorphic rocks.The ZTR index of heavy minerals in the Middle Triassic of funing-guichao basin shows that the provenance areas are mainly distributed in the south.Combined with previous studies on paleocurrent,it can further indicate that the basin supplies detrital materials from south to north.Based on the analysis of detrital zircon U-Pb ages of the Baifeng formation in the Middle Triassic and the comparison of the ages of the volcanic rocks in the south,it is found that the volcanic rocks provided part of the provenance for the basin in the early Middle Triassic,and the materials from Caledonian orogenic belt were also added.According to the field geological survey,there are volcanic rocks in the south of this set of sediments.Combined with the comprehensive analysis of fan delta facies,shallow sea shelf facies,turbidite fan facies and heavy mineral characteristics,it is inferred that the basin is likely to be a back arc basin.