Geologic Features, Provenance Analysis And Structural Evolution Of Maerzheng Formation At The Buqingshan Area In The Southern Margin Of The East Kunlun Region

The composition of sedimentary rocks is closely related to their tectonic background,and material sources of sedimentary rocks is determined by the provenance of rock types and tectonic environment,the results of the provenance analysis of sedimentary rocks has been widely used in the recovery of the ancient continental environment,growth of crustal evolution,while the basin-interaction of mountains.With the development of analysis methods,provenance analysis of sedimentary rocks has become a valid point of research of the relationship between sedimentary basin and orogenic belt,further inversion of source rock characteristics,basin tectonic environment, and reappear sedimentary basin objective to adjacent orogenic belt spatio-temporal coupling relation.In situ deposition system distribution in southern margin of the east kunlun mountains tectonic melange belt,the Maerzheng Formation,it is an important sedimentary response of the Paleotethys Ocean evolutionary stages,clarifing the nature of the basin and material sources and to understand the tectonic evolution history of the study area has special significance.Therefore,this paper application of the combination of sedimentary petrology,detrital component statistical analysis, rock geochemistry, detrital zircon isotope chronology and such disciplines as structural analysis method to comprehensive research Maerzheng Formation material characteristics.Systematic analysis of the nature of the basin and material sources, and on this basis,rebuilt the southern margin of the east kunlun mountains tectonic melange belt tectonic evolution process since the late Paleozoic.At the same time,some new advances and preliminary cognitions are proposed as follows:1、The study on detrital component statistic shows that main types of sandstone is feldspathic litharenite.Collect20samples of sandstone at Gerizhuotuo area,show that quartz,feldspar and lithic is44%,21%,35%,respectively,quartz is mainly single-crystal quartz,88%of the amount of quartz,the content of sedimentary lithic,volcanic lithic,metamorphic lithic respectively accounts for41%,37%,22%of the total lithic,while collect20samples of sandstone at Delistan area,show that quartz,feldspar and lithic is42%,37%,21%,respectively,the content of volcanic lithic, sedimentary lithic, metamorphic lithic respectively accounts for25%,39%,36%of the total lithic, sedimentary lithic is accounts most and is given priority to with flint lithic and limestone lithic.Petrography research indicate that if the content of quartz for sandstone more than40%,show that he sedimentary environment is relatively stable,the Dickinson diagrams show that provenance is mainly divided from orogenic belt and recycled island arc in category.2、The study of detrital zircon U-Pb age shows that detrital zircons in sample11061-4from Maerzheng Formation has5age groups including396～573Ma、727～947Ma、1117～1243Ma、1559～1993Ma、2319～3063Ma.The396～573Ma group has23zircons that accounts for about38%of the total,it is the largest a group that the characteristics of the strongest peak of421Ma,futher be subdivided into396～449Ma (18zircons) group and490-573Ma (5zircons) group. The samples of detrital zircon U-Pb age reflect information of4stages that is Caledonian, Neoproterozoic, Mesoproterozoic and Proterozoic-Archean,at sametime is given priority to Caledonian period age group.Integrated regional geological data in the study area,analysis that the metamorphic crystalline basement of orogenic belt of east kunlun could provide source material and from age spectrum contrast,the Caledonian magmatic arc at northern east kunlun is the most important provenance for Maerzheng Formation.3、The study of sandstone geochemical characteristic shows that collect15samples of sandstone at Gerizhuotuo area that SiO2values of58.12%～72.98%,average value of67.77%,the REE distributing patterns show rightward incline and weaker negative Eu anomaly,�'∑LREE/∑REE=6.5～12.1,δEu=0.63～0.75,CIA=56,while collect18samples of sandstone at Delistan area that the SiO2values of50.18%～74.05%,average value of66.69%,CIA=43～69,∑REE/∑REE=6.6～8.8,LaN/YbN=6.6～10.7,LaN/SmN=3.2～4.6,δEu=0.59～1.04.The lower CIA indicates that source rock by primary weathering intensity and have the near source sedimentary characteristics.The results indicate that tectonic setting belong to continental island arc type,the provenance is Caledonian magmatic island arc orogene and metamorphic basement of northern East Kunlun block,the sedimentary basin is the deep sea-bathyal basin.4、According to depositional characteristics,the Maerzheng Formation extensively develop Graded flysch,and is given priority to with continuous incomplete type.Complete Graded flysch extensively develop at the Delistan area,while different lithologic stratigraphic development in a variety of primary sedimentary structure reflect that the characteristic of the deep sea-bathyal facies turbidity current deposits.This paper according to the paleontological data,angle unconformity surface and detrital zircon U-Pb age determine the Maerzheng Formation the formation of early-middle Permian.5、Based on the comprehensive analysis about the deformation characteristics of the units and the boundary faults between the four geological units of the Maerzheng Formation of southern margin of the East Kunlun region,the formation fold deformation of late Permian,and mixing with oceanic crust form sedimentary rock.In the late Trias sic,occur strong oblique collision events,whlie the rock structure mixed. Late Triassic to early Jurassic continuous extrusion makes Shuweimenke Formation nappe tectonic melange belt of Buqingshan.Due to stretching rift in paleogene that the fault development of the surface.6、Combination with the regional geological background and the various aspects information,the results indicate that tectonic setting belong to continental island arc type,while provenance is mainly divided from orogenic belt and recycled island arc in category,the provenance is the Caledonian magmatic island arc orogene and metamorphic basement of northern East Kunlun block,the sedimentary basin is the deep sea-bathyal basin.Comprehensive regional magmatic activity and events and the tectonic deformation characteristics of the studied objects,the tectonic evolution of the study area can divide into five evolution stages,oceanic crust formation stage in early Carboniferous,oceanic spreading stage from late Carboniferous to middle Permian, the oceanic crust subduction stage from late Permian to middle Triassic,demise of the oceanic basin and collide-to-orogenesis stage at the end of Triassic,Cenozoic intracontinental orogenic stage.