Petrology And Geochemistry Of Late Paleozoic Granitoids In The West Junggar Metallogenic Belt(Xinjiang), Central Asia, And Tectonic Implications

The West Junggar Metallogenic Belt(WJMB), south of Sawuer Mountain in Northern Xinjiang province and located in the intersection of three continental plates(Siberia, Kazakhstan and Tarim) belongs to the northern accretionary edge of the ancient Kazakhstan plate. It is a north-east block held between the Tianshan fault system and the Irtysh fault, and belongs to a very significant part of the Central Asian Orogenic Belt(CAOB). Meanwhile, the West Junggar tectonic system is also very different from NW trend right-lateral strike-slip Aibihu fault of the Central Asian Orogenic Belt and E-W trend left-lateral strike-slip Irtysh fault in the north of West Junggar. Most structural lines in this region is to the NE-NEE trend, and compressive and torsion structure plane is in the main part, develops NE-trending domino-like left-lateral strike-slip faults system. Geological structure is more complex and different directions folds and faults are developed in this region, and obviously control the distribution of granite. Large-scale strike-slip movement may cause structural rotation of the blocks.In this paper, the author is focus on the relationships between structural tectonics and magmatic activities, and structural deformation in the West Junggar Metallogenic Belt(Xinjiang), CAOB. About 33 samples from 11 granitoid plutons had been collected in the Miaoergou and Bielu’agaxi areas in the NW side of the Dalabute fault of the West Junggar Metallogenic Belt. Research shows that structural deformation in West Junggar is very intensive, especially the north-south trend compression and north-east trend strike-slip; Miaoergou- Akebasitao "double intrusion bodies" have occurred counterclockwise structural rotation. We also determine the tectonic environments of the West Junggar granitoids through geochemical analyses and isotopic tracing. The Late Carboniferous granitoids in the Hatu area are mainly A-type ones formed in the post-collisional extensional tectonic setting. Meanwhile, adakites formed in the Bielu’agaxi area due to intra-ocean plate subduction. The results show the complicated tectonic setting in the West Junggar. All these granitoids have characteristic high εNd(t) ranging from +4.62 to +7.53, and value of εSr(t) ranging from –57.61 to +18.21, are suggested to be the Paleozoic formed continental crust with affinity to the depleted mantle source, which are similar to those in orther parts of the CAOB. The values of 206Pb/204 Pb, 207Pb/204 Pb, and 208Pb/204 Pb are ranging in 18.2776- 19.1677, 15.5260- 15.5796, and 38.2080- 39.0821, respectively, suggesting an orogenic setting for the granitoids, similar to those granitoids form the Tianshan Mountains, the Altai Mountains, and the Balkhash metallogenic belt. According to the structural geological relationship, the West Junggar and the Balkhash are considered to be once a continuous E-W-trending tectonic-magmatic-metallogenic belt in the western part of the CAOB.