Study On Geochemistry And Tectonic Environment Of Intrusive Rocks In North Qaidam ShaLiuQuan

In this paper, the author use the views of magmatic evolution sequence in the study area to establish the evolution of five magmatic series from three Magmatic belt according to magmatic rocks as the research object in Shaliuquan,Qinghai Province. The sequence from north to south were called Yiketaoli Magmatic belt include Hujirite Gabbro Sequence, Hujirite Granodiorite Sequence; Shaliuquan Magmatic belt include Amuneike Sequence, Nuoriha Sequence; Maoniushan Magmatic belt include Lama Tolgoi sequence. The author systematically analysis the study area by some effective methods which is called petrology, petrochemistry, earth rare-trace element geochemistry and isotope geochronology, and determine the diagenetic environment of the intrusions on the basis of this study, and concluded the tectonic environment at that geological time to provide the evidence for the tectonic evolution of North Qaidam basin.The study area is a relatively strong magmatic activities area, the magmatic activities was began in the Proterozoic and beyond the Mesozoic. Particularly in the Neoproterozoic and Hercynian,magmatic activity was over development. basic-ultrabasic rock emplacement occurred in Neoarchean and Acidic magma emplacemen occurred in the Early Permian and Late Triassic. Faults was strongly developed in the study area. On the whole,the large faults called Hudesheng is the boundary, the north of the fault is the upheaval called Kekesai and the south belongs to Ulan basin,The large faults is samely the Boundary of the Lower Proterozoic and Proterozoic, and also controls the Triassic and Mesozoic intermediate-felsic intrusion.Magmatic belt called Yiketaoli, the two Sequence invade within the Changcheng rock group in Proterozoic. According to the main elements of analysis, the sequence are Tholeiitic series. According to the analysis of rare earth trace elements and REE patterns characteristic graph, the Sequence Hujirite Gabbro Sequence is the Mantle origin; Hujirite Granodiorite Sequence is the Crust origin;According to the tectonic discrimination diagrams analysis, in Proterozoic, the sequence of geological environment is Active continental margin.Magmatic belt called Shaliuquan, the two Sequence invade within the Changcheng rock group in Proterozoic. According to the main elements of analysis, the sequence which Al saturation(A/CNK)> 1.1, are peraluminous. According to the analysis of rare earth trace elements and REE patterns characteristic graph, f the granite of the Sequence has a certain similarity with the crust granite. By U-Pb zircon test, the emplacedl age of the rock of the sequence is about 415-418 Ma.According to the tectonic discrimination diagrams analysis, the sequence of geological environment is from Active continental margin into Orogenic stage which produced Kekesai Uplift in Silurian.Magmatic belt called Maoniushan, the Sequence called Lama Tolgoi invade within Devonian of the Mesozoic rocks group. According to major element analysis, the Igneous are sub-alkaline series. According to the analysis of REE patterns characteristic graph, the graph performance the right tilt characteristics which are similar to the crust and indicate that source of the sequence rocks is the crust. By U-Pb zircon dating, the measured geological age of the rock of sequence is about 209 Ma. According to the tectonic discrimination diagrams analysis, the sequence of geological environment is the Stage of development of inland basin which produced Wulan Rift basin.Based on the above analysis, the study area experienced the process of which the north of the Hudesheng Fracture is a compression uplift and the south is extensional rift in the Proterozoic- Mesozoic. Structural faults is strong development in the study area,and the structral faults is play a significant role in the evolution of the area. The main direction of the tectonic line in the study area is the North West-South East. The stratum should be force the NE-SW compressive stress and occur uplift in the north of Hudesheng fault. Samely,the stratum of the Wall strata is produced a series Reverse faults bacause of the the NE-SW compressive stress.Later,the south and north of the large faults is produced a series Strike-slip fault continue by the the NE-SW compressive stress. Finally, the area called Maoniushan is developed the rift basin bacause of the pulling tension.