新疆铁克里克西段都维吐卫岩体年代学、岩石地球化学特征及地质意义

出露于新疆塔里木南缘铁克里克地区西段的都维吐卫花岗岩体, 侵入赫罗斯坦岩群(Pt1H)黑云二长片麻岩中, 与库浪那古岩群(Pt2K)和大同西岩体呈断层接触, 东部多被博查特塔格组(Jxbc)不整合覆盖。通过地球化学分析, 显示岩体具高Si、高Al、高K, 贫Na、低Ga、低P、低Ti和贫Mg的特征, 铝饱和指数(A/CNK)为1.38~1.43, CIPW标准刚玉分子大于1%, 属高钾钙碱性过铝质花岗岩。在稀土元素方面显示, 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=0.59~0.82);在微量元素方面, 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。岩体LA-ICP-MS锆石U-Pb同位素定年获得年龄为(1 909±47)Ma, 属于古元古代花岗岩。综合分析认为该岩体是造山晚期-同碰撞环境下形成的, 与加厚地壳引起的地壳重熔有关, 推断西昆仑造山带强烈的陆内造山活动应在古元古代已经开始了;结合赫罗斯坦岩群(Pt1H)中角闪斜长片麻岩中锆石年龄记录, 推断2 000~1 800Ma塔里木陆块存在Columbia超大陆聚合事件。

Chronology,Geochemical Characteristics and Geological Significance of the Duweituwei Granite in Western Tiekelike of Xinjing

The Duweituwei granite exposed in western Tiekelike area of the southern Tarim Basin of Xinjiang intrudes into biotite monzo-gneiss of Heluositan terrain (Pt1H), and contacts by fault withthe Kulangnagu(Pt2K) terrain and west Datong granite. Besides, the east of the granite is unconformably covered by Bochatetage group (Jxbc). Geochemical analysis shows that the granite has high SiO2, Al2O3, K2O content but relatively low CaO, P2O5,TiO2 and MgO content.The ratios of A/CNK vary from 1.37 to 1.43, and CIPWcorundum molecule is larger than 1%, suggesting its type of high-K calc-alkaline peraluminous syn-collision granite. The chondrite-normalized REE patterns show that the granite is rich in LREE but depleted in HREE, with high fractionations between LREE and HREE and moderate negative Eu anomalies (δEu is 0.59 to 0.82). 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 in the primitive mantle-normalized trace elements patterns. Zircon LA-ICP-MS dating yielded the age of (1 909±47)Ma, implying that the magmatic crystallization epoch of the granite is late Paleoproterozoic.Comprehensive analysis suggests that the rock mass is formed in the late orogenic collision environment relevant to the formation of thickened crust induced crustal remelting. It is therefore speculated that the strong intracontinental orogenic activityin western Kunlun orogenic belt should have begun in the Paleoproterozoic.Combined with the zircon record of hornblende plagioclase gneiss in Heluositan rock group(Pt1H), it is inferred that the Columbia supercontinent events occurred in the Tarim block during 2 000 to 1 800Ma.