Geochemical Characteristics And Tectonic Implications Of Kulumusu-Kezilekeya Granites In West Junggar, Xinjiang

This paper takes the modern theory of plate tectonics as the academic guiding ideology. It uses comprehensive research methods of the geology to give Kulumusu-Kezilekeya granites in West Junggar systematic analysis about petrology and geochemical characteristics. Through these methods above, we can determine the rock types, causes, and tectonic setting, and then provide new evidence for the inversion of the tectonic evolution of West Junggar. In this paper, conclusions are as follows:1. Kulumusu granites (LA-ICP-MS zircon U-Pb age of324.3±8.2Ma, Early Carboniferous) have the characteristics of high silicon (SiO2=71.08-78.35wt.%), low aluminum (Al2O3=11.66-14.38wt.%), rich alkali (Na2O+K2O=8.19-9.42wt.%), poor calcium (CaO=0.23-1.25wt.%, average:0.61wt.%), low magnesium (MgO=0.02-0.34wt.%), low titanium (TiO2=0.04-0.30wt.%, average:0.17wt.%), rich potassium and poor sodium (K2O/Na2O=1.01-1.37, average:1.14), quasi-aluminous (A/NKC=0.91-0.96); enriched in Rb, Th, K, LREE, etc, depleted in Ba, Nb, Ta, Sr, P, Ti, etc,(La/Yb)N=3.5-5.28, intense negative Eu anomalies (8Eu=0.01-0.31). Kulumusu granites are high-K calc-alkaline A2-type granites.2. Kezilekeya granites (LA-ICP-MS zircon U-Pb age of301.1±3.4Ma, Late Carboniferous) have the characteristics of high silicon (SiO2=74.26-76.15wt.%), low aluminum (Al2O3=12.59-13.34wt.%), rich alkali (Na2O+K2O=8.69-9.46wt.%), poor calcium (CaO=0.25-0.33wt.%, average:0.28wt.%), low magnesium (MgO=0.13-0.18wt.%), low titanium (TiO2=0.24-0.32wt.%, average:0.27wt.%), rich potassium and poor sodium (K2O/Na2O=1.20-1.49, average:1.14), quasi-aluminous (A/NKC=0.91-0.96); enriched in Rb, Th, K, LREE, etc, depleted in Ba, Nb, Ta, Sr, P, Ti, etc,(La/Yb)N=3.31-10.01, intense negative Eu anomalies (δEu=δEu=0.22-0.31). Kezilekeya granites are high-K calc-alkaline A1-type granites.3. The Y/Nb value of Kulumusu granites and Kezilekeya granites are3.9-8.2(>1.2) and0.74-1.14(<1.2) respectively. Both of them are formed in the post-collisional extensional environment. But Kulumusu granites are products of and the lower crust partial melting. The cause of Kezilekeya granites is that the pre-existing metasomatic enriched veins (dykes) in the lithosphere mantle melt partly due to diapirism and heating effect of the asthenospheric mantle.4. Based on research on Kulumusu granites and Kezilekeya granites, comprehensive comparison with other plutons in the study area, this paper can infer that: the plate evolution transformed into post-collisional extensional stage in West Junggar in late Early Carboniferous; the ancient ocean represented by Hongguleleng ophiolite had closured and collided in early Early Carboniferous.