新疆库鲁克塔格阿訇开里得南石炭纪花岗岩LA-ICP-MS锆石U-Pb定年及其地质意义

摘要

对出露于新疆库鲁克塔格地块西段的阿訇开里得南花岗岩进行了详细的岩石学、地球化学及锆石U-Pb定年研究,并探讨了其构造背景及地质意义.岩体LA-ICP-MS锆石U-Pb原位定年获得年龄为340.6Ma±5.7Ma,属于石炭纪花岗岩.地球化学分析显示岩体具高硅、高铝、高钾,贫钠、低钙、低磷、低钛和贫镁的特征,铝饱和指数(A/CNK)为1.14～2.31,CIPW标准刚玉分子大于1％,属高钾钙碱性过铝质花岗岩.在稀土元素球粒陨石标准化配分模式图上,轻稀土元素(LREE)富集、重稀土元素(HREE)亏损,轻重稀土元素分馏明显,Eu出现中等负异常(δEu=0.52～0.62)；在微量元素原始地幔标准化蛛网图上,明显富集大离子亲石元素Rb、Ba、Th和K,亏损高场强元素Nb、Ta、Ti.综合分析研究认为,岩体的形成与加厚地壳引起的地壳重熔有关,反映了塔里木板块与伊犁-中天山板块陆-陆碰撞的岩浆活动.%The South Ahongkailide Carboniferous granite is exposed in the west segment of Kuruktag block in Xinjiang. This paper has studied petrographical, geochemical and zircon U-Pb chronolgical characteristics of this granite as well as its petrogenesis and geological significance. Zircon LA-ICP-MS dating yielded the age of 340.6Ma±5.7Ma, implying that the magmatic crystallization epoch of the granite is Carboniferous. Geochemical analyses show that the granite has high SiO2, A12O3, K2O but relatively low CaO, P2O5, TiO2 and MgO. The ratios of A/CNK vary from 1.14 to 2.31, suggesting high-K calc- alkaline peraluminous syn-collision granite. The chondrite-normalized REE patterns show that the granite is enriched in LREE but depleted in HREE, with high fractionations between LREE and HREE and moderate negative Eu anomalies ((δEu=0.52～0.62). In addition, the granite is relatively rich in such LILEs as Rb,Ba.Th and K, but poor in such HFSEs as Nb, Ta and Ti, with relative enrichment of Ce in the primitive mantle-normalized trace elements patterns. The authors have come to the conclusion that the formation of the granite was closely related to crustal partial melting caused by crustal thickening and represented the magmatic activities during the coUisional event between Tarim plate and Yili-Central Tianshan plate.