Study On The Geological Characteristics And Tectonic Attribute Of Granite In Buqingshan Kekeerta Area, The South Margin Of East Kunlun Mountians

Located in the transition region of East Kunlun orogenic belt, West Qinling orogenic belt,Bayan Har Orogen belt, A’nimaqing-Buqingshan tectonic belt is the key areas to research structure of continent of China and continental dynamics. This study choose granite rock located in Kekeerta areas of southern edge of Eastern Kunlun as the research object. Through the study of detailed field geological investigation, Tectonic, lithology, rock geochemistry and isotope chronology, based on the theory of plate tectonics and the latest achievements and theory of continental dynamics, combined with previous study, this paper is to explore the formation age and tectonic environment of granite rock in Kekeerta areas as well as Early Paleozoic tectonic evolution of Buqingshan areas. The following are the results:1. The medium-fine grained porphyritic biotite granodiorite in southern Kekeerta areas was emplaced in the middle-proterozoic Kuhai group complex( Pt2K),Geochemical characteristics show that its aluminum saturation index A/CNK value between 1.01 and 1.09,it belongs to weakly peraluminous high-k calc-alkaline series I type granite,similar to arc calcium alkaline magma series, the amount of its rare earth element is on the low side and its light REE are riched with weak Eu negative anomaly. LA-ICP-MS U-Pb zircon dating result shows diagenetic age of biotite granodiorite in southern Kekeerta was 422.5 ± 1.2Ma(MSWD=0.53), as Late Silurian epoch. Rock mass formed in island arc or continental arc environment related to the subduction.2. The fine grained biotite granodiorite in northern Kekeerta areas was emplaced in the middle-proterozoic Kuhai group complex(Pt2K),geochemical characteristics show that its aluminum saturation index A/CNK value between 1.05 and 1.09 with average of 1.07, it belongs to weakly peraluminous potassium calc-alkaline series I type granite; Geochemistry indicate molten magma formed its magma source is basststic rocks of thickened thickened lower crust and mantle wedge by contamination LA-ICP-MS U-Pb zircon dating result shows diagenetic age of biotite granodiorite in northern Kekeerta was 403±2Ma(MSWD=2.2), as Early Devonian. Rock mass formed in the tectonic environment from syn-collision to postcollision.3.Medium-fine grained block granodiorite in Herigougongmaer is exposed in permian Maerzheng group(P1-2m)and its contacting with on both sides of the formation is fault,geochemical characteristics show that it belongs to weakly peraluminous potassium calc-alkaline series I type granite and its aluminum saturation index A/CNK value is 1.07;Geochemistry indicate molten magma formed its magma source is Na rich basststic rocks ofthickened lower crust and mantle wedge by contamination LA-ICP-MS U-Pb zircon dating result shows diagenetic age of medium-fine grained block biotite granodiorite in Herigougongmaer was 398±2Ma(MSWD=2.2), as Early Devonian. Rock mass formed in the tectonic environment from syn-collision to post-collision. Comprehensive studies have shown that medium-fine massive granite diorite in Herigougongmaer and fine grained biotite granodiorite in northern Kekeerta areas have similar petrological and geochemical characteristics. They formed almost the same time which may represent the same issue of tectonic-magmatic events as well as forming in the same tectonic environment.4. There was Early Paleozoic ocean-land conversion in East Kunlun and Late Silurian-Early Devonian is the main orogenic period of this areas. Formation of granite rock mass in Kekeerta areas may be related to Early Paleozoic ocean-land conversion and continent-continent collision orogeny in East Kunlun.