A Study On Geologic Feature And Structural Setting Of The Lower Triassic Hongshuichuan Formation In Eastern Section Of The East Kunlun Orogen

This paper mainly relys on the regional geological and mineral survey project “1∶50000regional geological and mineral survey in Alakehu—Hongshuichuan area of Dulan couty,Qinghai Province” from Department of Land and Resources of Qinghai Province—AluminumCorp. of China project. Through field geological mapping and reseach for the measuredsections, the dissertation managed to make detailed investigation and regional comparison forthe Lower Triassic Hongshuichuan Formation. After finishing the field investigation andstudy indoor systematically, on the basis of previous achievements, we make a new divisionon the Hongshuichuan Formation. It can be divided into six lithologic section from bottom totop. The first lithologic section (T1h1) is grey-green—purple coarse clastic rock assemblage,the second lithologic section (T1h2) is the grey-green coarse clastic rock assemblage, the thirdlithologic section (T1h3) is dark grey thinly laminated limestone assemblage, the fourthlithologic section (T1h4) is fine-grained clastic rock assemblage, the fifth lithologic section(T1h5) is turbidite assemblage, the sixth lithologic section (T1h6) is fine-grained clastic rockassemblage. The Lower Triassic Hongshuichuan Formation in the study area is distributedmainly in southern margin of East Kunlun Orogen, and is mainly clastic rock composed ofconglomerate, sandstone and calcareous siltstone, containing small quantities of carbonatesuch as limestone, crystalline limestone and bioclastic limestone. According to comprehensiveanalysis of existing and previous data, the sedimentary facies types of HongshuichuanFormation in the study area mainly include the fan-delta depositional system, the shallowwater diamictite continental shelf depositional system, the bathyal turbidite deposition system,as well as the coastal and offshore depositional systems. According to the comprehensiveanalysis of three-component statistics in petrographic thin section and related information, weconclude that the sandstone source of Hongshuichuan Formation is mainly magmatic arc inthe north, the provenance should be formed in a relatively simple tectonic setting in the sourcearea. The majority of the sandstone from Hongshuichuan Formation in the study area fall intothe dissected arc region, except minority fall into the recycling orogenic belt. We concludethat the sandstone source area may be the continental margin arc setting. The fore-arc basindepositional system records indirectly the developing process of northward subduction of theBuqingshan—A’nimaqing ocean.