Provenance Analysis And Structural Significance Of Niubao Formation In Saibucuo Area,Tibet

The geological information of Saibucuo area in Bangong-Nujiang suture zone,Qinghai-Tibet Plateau is conducive to restore its tectonic paleogeography and provides sedimental evidence for the Qiangtang-Lhasa terrane collision process.Currently,studies of the Niubao formation in this region are relatively weak.Based on the previous scientific research,by obtains the field profile and paleo-flow data of the Niubao formation,and basing on the sedimentary stratigraphy and petrography to analyze the sedimentary environment characteristics of this area.This paper analyzes the sedimentary environment and provenance of the Niubao formation in this area by the palaeoflow analysis,detritus sandstone analysis,and detrital zircon U-Pb chronology and so on.The results of sandstone analysis show that Niubao formation sandstone is dominated by lithic quartz sandstone,which has the most quartz grain and is well preserved,followed by lithic and mainly composed of volcanic lithic,while feldspar is mainly composed of plagioclase and weathered a lot.The source rock underwent long-term weathering,transportation and redeposition.Sedimentary environment analysis results show that the sedimentary facies in the Saibucuo area is delta-fluvial facies.Zircon U-Pb ages range from 38 to 63 Ma,110 to 121 Ma,220 to 235 Ma,448 to 568 Ma,1753 to 1927 Ma,2456 to 2578 Ma.The results of provenance analysis show that the material sources of the Niubao formation detrital rocks are the tectonic melange belts of Qiangtang-Lhasa terrane and thrust nappe structures,and the igneous rocks of Cretaceous and Linzizong igneous rocks also provide provenance.According to the analysis results of the Niubao formation,the palaeo-current was southward and northward in middle to late Eocene,and there was a connected channel with the Nima basin.According to the analysis results of the provenance and regional tectonic background,the tectonic model of the Saibucuo area is a depression basin controlled by the thrust fault in northsouth compression environment.