Geological Characteristics,Provenance Analysis And Tectonic Evolution Of The Volcanic-sedimentary Strata Of The Maoniushan Formation In The Hongshuihe Area Of The Eastern Kunlun Orogenic Belt

The East Kunlun orogenic belt with a long history of evolution is located in the northeastern part of the Qinghai-Tibet Plateau and the central and western part of the Central Orogenic System..It is a continent formed by different types and stages of orogenication.Composite orogenic belt.The central eastern Kunlun tectonic melange belt is divided The East Kunlun orogenic belt into the Dongkunbei tectonic belt and the Dongkunnan tectonic belt.It is a regional giant tectonic deformation zone and is an ideal for studying the original Tethys-Guttis structural transformation and composite orogenic effects.The test base has a very high research value.In this paper,the theory of plate tectonics and the study of continental dynamics are used as the guiding ideology.The theory and methods of modern tectonic geology are used as the means to obtain the first-hand information obtained through actual observation and observation in the field and combined with detailed indoor research.The spatial distribution,structure,material composition,sedimentary petrology and U-Pb isotope chronology of Detrital zircon of the Maoniushan Formation in the East Kunlun Mountains are sorted out,studied and summarized.Based on the research results of predecessors in this area,the following understandings are obtained.(1)Through the petrographic analysis of the Maoniushan Formation,the sandstone type of the Maoniushan Formation is mainly lithic sandstone,The content ranged from 66% to 83%,indicating that its maturity was low.According to the combination of rock characteristics and sedimentary environment,the Maoniushan Formation will be divided into three lithologic member.the lower member is boulder,coarse conglomerate and pebbly coarse sandstone,with a small amount of basalt interlayer,which is a fast high-energy environment in the mainland.Mixed accumulation,belonging to the alluvial fan deposition system.The middle member is a fine clastic rock section with pebbly sandstone,coarse sandstone,fine sandstone and silty mudstone,with a small amount of medium conglomerate and fine conglomerate,which should be a braided river sedimentary system.The upper member is a volcanic membe,of which the volcanic rocks are mainly light gray-green rhyolite andesite,rhyolitic,gray-green thick layered basalt,and the sedimentary rocks are mainly a large number of silty rock and silty mudstone.The they showed a gradual transition and appeared in each other,and the overall grain size gradually became thinner,showing the sedimentary characteristics of the lacustrine facies.(2)Based on the statistical analysis of the clastic composition of sandstone samples in the section of Maoniushan Formation,the clastic provenances of Maoniushan Formation are mainly from the the recycling orogenic belt and a few mixed orogenic belts.Major and trace element analysis of sandstone indicates that the source area of Maoniushan Formation is mainly feldspathic rocks,and there are mature continental quartz sediments.Geochemical analysis shows that the tectonic background of the source area is mainly active continental margin,and some are from passive continental margin or continental island arc.In addition,combined with the diagrams of continental rift alluvial fan(AF)and lacustrine sedimentary area(LB)summarized by Huntsman-Mapila et al,it is concluded that the basin type of the Maoniushan Formation is intracontinental rift basin.(3)The analysis of the two detrital zircon samples obtained from the Maoniushan Formation in the Hongshuihe area shows that the minimum age obtained in the Maoniushan group is 421.4±10 Ma,which can represent the lower limit of the sedimentary age of the Maoniushan Formation,combined with the yak in the area.The age of foliated dacite in upper part of the upper Member of the Maoniushan Formation is 409.5±4.6 Ma,and the formation age of the Maoniushan Formation in the study area was limited to to late Silurian to early Devonian.(4)By collecting the age information of various magmatic events reported by predecessors in the region and comparing with the age spectrum of detrital zircons obtained from older strata in the study area or adjacent areas,it is considered that the provenance of the Maoniushan Formation may come from the Archean continental core of East Kunlun,and the age of Paleoproterozoic to Mesoproterozoic may come from the Paleoproterozoic basement of East Kunlun and the northern margin of Qaidam.The age may include the information of the splitting of the Columbia supercontinent in the eastern Kunlun and Northern Qaidam basin and the numerous thermal events in the early stage of the Rodinia supercontinent aggregation.The age of Neoproterozoic may reflect a series of thermal events in the process of aggregation-splitting around Rodinia in the eastern Kunlun orogenic belt and the northern Qaidam basin.Age information of Paleozoic mainly comes from a series of oceanic ridge ophiolites,SSZ ophiolites,active continental margin magmatic arcs and post-collisional granites produced during the expansion-subduction-extinction of the former Tethyan Ocean in the eastern Kunlun region,and tectonic-thermal events occurring during ocean-continental subduction and later land-land collision in the northern margin of Qaidam Basin may also provide them.Part of the provenance.Based on the age information of clastic zircon and its peak value,and comparing with the age of rock mass exposed in adjacent area,it is further considered that Neoproterozoic and Early Paleozoic granites intruded into Baishahe Formation and Xiaomiao Formation,volcanic rocks of Nachitai Group formed in active continental margin background,and early Paleozoic continental margin arc-type granites in eastern Kunbei magmatic arc.Rocks and collisional-post collisional granites are the main provenances of the Maoniushan Formation.The Nachitai Group provides a large amount of detrital material.In addition,The Paleoproterozoic-Mesoproterozoic crystalline basement mainly Mainly including Baishahe Formation and Xiaomiao Formation also provided a small amount of provenance for the Maoniushan Formation.