Initial Research on Formation and Mineralization of Granite in Eastern Bogda Orogen, XinJiang

Abstract: The Xidi-Yiqi region, which is in the north of eastern Bogda orogen and joined to Jungar massif in the north and Jungar orogen in the east, belongs to the tectonic zone of north Tianshan, and the geotectonic position is very important. So the studying area is an important location to research the kinesiology and dynamics of Tianshan orogen, attracting more and more geologists. The article, guided by the plate tectoics and tectonic magmatism, studies the petrology, petrochemistry, geochemical characteristics and the forming age and minerogenic conditions of Xidi-Xiaohongliuxia granitoids using the field geologic survey and indoor analysis.The Xidi-Yingpan terrene uted mainly by high-K calc-alkaline granites, is an acidic intrusion, and the U-Pb age of individual zircon grains (364- 370Ma) indicates the forming age of granites. The age proved the stratum belongs to Dananhu Group in early Devonian epoch considered to be late Carbonic epoch. The terrene has enriched Na and depleted K, w(Na_2O)=4.16%-4.39%,w(K_2O)=3.08%-3.47%, w(Na_2O/K_2O) =1.37, w(SiO_2)=69.5%-71.4%, Al_2O_3=13.89%- 14.30%. The rocks belong to calc-alkaline series and slight peraluminous(A/CNK<1.1), and project in the I-type granite area in K_2O-Na_2O diagram. The REE characteristics are∑REE=107.4×10~(-6)-136.8×10~(-6), Y/Nb>8, La/Yb>8, LREE enriched, HREE depleted, (La/Yb)N>5 and slight neglect Eu anomaly, similar to the characteristics of I-type granite and Kelamaili I-type granite.δ~(18)O(δ~(18)O=6.8‰) indicates the magma is crust-mantle mixed source, or contaminated by the crust in the intrusive process of mantle magma. The ORG-normalized and PM-normalized spider diagrams show the obvious neglect Nb, Ti anomalies and enriched strong incompatible elements, and relative neglect P, Sr anomalies and positive K anomaly indicate the fractional crystallization of plagioclase. Y-Nb, (Y+Nb)-Rb, Yb-Ta, (Yb+Ta)-Nb, Hf-Rb/10-Ta×3 and Yn_N-(La/Yb)_N diagrams show the granites formed in island arc/continental marginal arc setting and are related to the partial melting of depleted mantle wedge replaced by the subducted fluid initiated from the subduction of Takezhale limited ocean basin, and the magma experienced the fractional crystallization and crustal contamination. Meanwhile, the field geological evidences show the magmatic evolutionary trend to feldspar granite. As a whole, the tectonic evolution of Bogda orogen is of multistage and polygenous- the evolutionary stage of island arc in late Devonian, inverted to rift evolution in Carboniferous period.The geochemical analysis indicates the granitoids have the characteristics of I-type granite, and the magma is crust-mantle mixed source. The hydrothermal actions of late magmatism provide the thermal power for the Cu and Au activations, which is a significant prospect to Cu deposit…
Key words: Geochemistry; granite genesis; volcanic arc; late Devonian; eastern Bogda orogen

This entry was posted in Master Thesis. Bookmark the permalink.