库米什地区二云母岗岩锆石LA-ICP-MSU-Pb定年及岩石地球化学特征

摘要

In Kumishen area the two-mica granite was emplaced in the Mesoproterozoic Xingxingxia group in eastern part of South Tianshan. LA-ICP-MS U-Pb Zircon U-Pb dating of one sample yield one concordant ages of 293.3± 1.3, indicating intrusive time of two-mica granite is early Permian. Geochemically, the rocks are rich in K (K2O/Na2O=l.39-2.09), with A/CNK values between 1.03 and 1.23, which belong to S-type granite. The rocks are also characterized by enrichment of LREE and LILE (K, Rb, Th and U) and depletion of HFSE (Nb, Ta, Sr, Ba, P and Ti), with low total REE (TREE=89.99x10-6~105.11xl0-6) and moderate negative Eu anomaly (δEu=0.38~0.55). Based on geological setting and geochemical characteristics, it is showed that two-mica granite source rocks derive from Xingxingxia Group metapelites. It is produced in a transitional tectonic setting from continental collision tectonic environment?of late orogenic epoch to post-collisonal, which probably represents completion of the collisional orogeny between Tarim plate and Yili-Kazakstan plate in Early Permian, as well as entering into a post-collisional evolution stage in Kumishi area in eastern part of South Tianshan.%出露于南天山东段库米什地区的二云母花岗岩体侵入中元古界星星峡群,通过锆石LA-ICP-MS U-Pb 法测得该岩体年龄为(293.3±1.3) Ma,侵位时代为早二叠世.岩石地球化学研究表明,岩石具高钾(K2O /Na2O=1.39～2.09) 和强过铝(A/CNK=1.03～1.23)特征,为典型S型花岗岩.岩石普遍具较低稀土元素总量(TREE=89.99×10-6～ 105.11×10-6)和中等铕负异常(Eu=0.38～0.55),富集轻稀土和大离子亲石元素K,Rb,Th,U及亏损高场强元素Nb,Ta,Sr,Ba等特 征.结合区域地质特征认为,库米什北二云母花岗岩源岩可能为中元古界星星峡群变质泥质岩,形成于碰撞晚期至后碰撞转 换阶段,揭示了南天山东段库米什地区伊犁-中天山板块和塔里木板块于早二叠世碰撞造山结束,进入后碰撞演化阶段.