Provenance Analysis And Geotectonic Significance From The Carboniferous Riwanchaka Formation Of Chabuxiang,Gaize County,Tibet

The study area is located in the central part of Qiangtang,Tibet,the middle part of the Longmucuo-Shuanghu suture zone,and the geographical location is near the southern part of gangmacuo in Chabu Township,Gaize County,Ali Region,Tibet Autonomous.The study of Riwanchaka formation is of great significance to the evolution of the Longmucuo-Shuanghu lake and the paleo Tethys ocean.In this paper,based on the 4 regional survey projects in the south of Rongma Township,1:50000 in Tibet,and under the guidance of the theory of sedimentary formation and geotectonics,on the basis of field geological mapping and measured sections,we use the means of zircon U-Pb dating,zircon Hf isotope analysis,whole rock geochemical analysis and observation statistics under the sedimentary clastic microscope to study the lower Carboniferous in the Gaize area of Tibet The provenance of the Riwanchaka formation is systematically studied and its geotectonic significance is discussed.The following innovations and understandings are obtained in this study:Field observation shows that the main body of the lower Carboniferous Riwanchaka formation is a set of limestone intercalated with clastic rocks,and the underlying strata are volcanic rocks of the lower Carboniferous wangguoshan formation.The youngest peak age range is 300-350ma(n = 35)in the clastic intercalation of Riwanchaka formation,which is consistent with the Early Carboniferous Sedimentary age shown by its internal fossils.At the same time,these zircons are poorly rounded,so they are a set of near source sediments.The epsilon?Hf(t)of zircon is negative,which means the source of remelting of ancient crustal materials.According to the observation and statistics under the microscope,the sandstone sample is feldspathic detritus sandstone with low maturity.The results show that the provenance type of Riwanchaka formation in Lower Carboniferous belongs to the cutting island arc provenance and the tectonic background is island arc.In the aspect of rare earth elements,light rare earth elements are relatively enriched and heavy rare earth elements are deficient,with obvious Eu negativeanomaly,which is similar to the distribution characteristics of rare earth elements in the continental crust.On the Zr/Ti O2*0.0001-Nb/Y discrimination diagram,the samples fall into the junction zone between rhyolite/dacite area and andesite area,indicating that the Riwanchaka material may come from the upper crust.In the environmental discrimination diagrams of trace elements La-Th-Sc and Th-Sc-Zr/10,almost all the sandstone samples of the Riwanchaka formation are in the continental arc.According to the above results,the volcanic rocks of the lower Carboniferous Riwanchaka formation and the lower Wangguoshan formation form a continental oceanic paleoisland arc terrane.In some of the high-pressure metamorphic rocks of Nanqiangtang,a peak value of 471-325 Ma of detrital zircon has been found.Since no provenance can be found in the surrounding terrane,it is speculated that it originated from the subduction of the ancient island arc terrane.The ancient island arc terrane composed of volcanic rocks of the lower Carboniferous Riwanchaka formation and Wangguoshan formation discovered in this study may be the protolith of the high-pressure metamorphic rock.Region.