Abstract:
Choosing the granites in Shaleketeng area in West Junggar as the research objects, this paper aims to discuss the regional tectonic environment by studying its petrological, geochronological and geochemical characteristics on basis of the fieldwork.The granites can be divided into four sequences: Shaleketeng, Chaganengan, Alaqiaogu and Tanzibulake.Shaleketeng sequence is composed by granodiorite-porphyry and monzonitic granite-porphyry, and formed in the Late Carboniferous, which zircon LA-ICP-MS U-Pb age is 302.1±1.4 Ma(
n=26, MSWD=1.5).Shaleketeng sequence is belong to quasi-aluminous to weakly peraluminous I-type granite characterized by relatively low SiO
2 (68.07%~70.49%) and K
2O+Na
2O(7.23%~8.18%), Al
2O
3(14.12%~15.69%), TiO
2(0.43%~0.48%)and CaO(1.71%~3.31%)in Major element compositions, and relatively depleted Nb, Ta, Sr, P, Ti and enriched Zr, Hf in trace element compositions.Chaganengan sequence is composed by alkali-feldspar granite and orthogranite, and formed in the Early Permian, which zircon LA-ICP-MS U-Pb age is 296.7±2.1Ma(
n=26, MSWD=0.41).Chaganengan sequence is belong to quasi-aluminous alkaline fractionated I-type granite characterized by relatively high SiO
2(74.21%~74.37%), K
2O+Na
2O (8.84%~9.19%), Al
2O
3(12.59%~12.85%)and low TiO
2(0.19%~0.22%), CaO(0.64%~1.24%) in major element compositions, and low REE and relatively depleted Sm, Th, Y, Yb, Lu, Sr, and enriched Zr, Hf in trace element compositions.Alaqiaogu sequence is composed by diorite, diorite-porphyry and quartz diorite-porphyry, and Tanzibulake sequence is orthogranite and monzonitic granite-porphyry, which are respectively belong to weakly peraluminous alkaline I-type granite and S-type granite.Considering the Regional geological data, the research reflects the granites in the studying area is formed in the transfer stage from compression to extension of post-collision tectonic environment, and Shaleketeng sequence indicates the time limit for the study area to enter the extensional stress system should be no later than 296.7±2.1 Ma.