The Disintergration, Geochemistry And Tectonic Implications Of The Kulumusu Granite Batholith In West Junggar, Xinjiang

Late Paleozoic granitoids are widespread in West Junggar and even in the whole northern Xinjiang. The Kulumusu granite batholith is a representative of these intrusions,located in the Wuerkashier, West Junggar. This paper takes the Kulumusu granite batholith as the research object, researching systematically from the field outcrop surveying, petrology, contact relationship, petrochemistry, magmas evolvement, and diagenetic epoch of the Kulumusu granite batholith, and has reached the following conclusions:1. The Kulumusu granite batholith is a composite batholith and could be disintergrated into two different intrusive series, one is Late Carboniferous Kulumusu series, and the other is early Permian Shaque series. The Kulumusu series mainly comprises monzogranite, fine-grained syenogranite, middle-coarse-grained syenogranite, alkali feldspar granite and K-feldspar porphyry, and the Shaque series mainly comprises quartz-diorite and quartz monzodiorite.2. High-precision LA-ICP-MS zircon U-Pb dating of the Kulumusu series indicates that the weighted mean 206Pb/238 U age are 291.5±2.9 Ma and 290.9±2.9 Ma, and that of the Shaque series are 304.9±2.5 Ma and 304.1±2.9 Ma. The ages of the two series show they formed in different magma intrusion events, providing geochronological evidence for disintergration of the Kulumusu granitic batholith.3. The Kulumusu series is characterized by high silica(SiO2: 70.78%~76.85%), alkali(K2O+Na2O: 7.87%~9.71%), and low titanium and calcium(TiO2: 0.08%~0.41%, CaO: 0.16%~1.42%), ranges from metaluminous to weakly peraluminous(ACNK: 0.98~1.15). The rocks display rare earth elements patterns with “V” shape, and evidently depleted in Eu. They are enriched in light rare earth elements(Rb、Th、K) and high strength field elements(Zr、Hf), significantly depleted in Ba, Sr, P Ti. These features indicate that the Kulumusu series belong to A-type granite. Element geochemical characteristics show that the Shaque series w(SiO2)=57.82%~66.18%, w(Na2O)= 4.86%~6.05%, A/CNK percent number is 0.81~0.97< 1.1, Rb/Sr=0.05 ~ 0.27 < 1, low K2O/Na2O(K2O/Na2O=0.22 ~ 0.77) and high Ca O(CaO=1.75~5.8), the REE patterns shows weak negative Eu anomalies, and the dark minerals of the Shaque series are mainly Biotite and amphibole, These features indicate that the Shaque series belong to I-type granite.4. This paper propose that the Shaque series was a product of partial melting of mantle wedge replaced by slab-derived fluid and suffered the contamination of crust during upward of magma. and the upwelling of asthenospheric mantle that induced by the breakoff of the subducted slab heated the lower crust then resulted in the partial melting of amphibolites and the formation of the Kulumusu series.5. Subduction was still underway during the Late Carboniferous and ended in the Early Permian, and then came in an extension setting of the post-collision stage.