新疆博格达东缘色皮口地区柳树沟组流纹岩地球化学、LA-MC-ICP-MS锆石U-Pb年代学及地质意义  

Geochemistry, Zircon U-Pb Ages and Geological Significance of the Liushugou Formation Rhyolite in the Sepikou Region, Eastern Bogda, Xinjiang

作　　者：高景刚[1,2] 李文渊[2] 周义[1] 刘建朝[1] 范庭宾[3] 鲁麟[1] 周汝洪[4] 

机构地区：[1]长安大学,西部矿产资源与地质工程教育部重点实验室,陕西西安710054 [2]西安地质矿产研究所,陕西西安710054 [3]新疆维吾尔自治区地质矿产勘查开发局第十一地质大队,新疆昌吉833000 [4]新疆维吾尔自治区地质矿产勘查开发局,新疆乌鲁木齐810000

出　　处：《地质与勘探》2013年第4期665-675,共11页Geology and Exploration

基　　金：中国地质调查局项目(编号1212011121092);新疆维吾尔自治区1:5万区域地质矿产调查项目(编号XJQDZ2008-05);中央高校基本科研业务费专项资金(编号CHD2010JC128);长安大学基础研究支持计划专项基金联合资助

摘　　要：新疆色皮口地区位于博格达造山带东段北部,区域内的上石炭统柳树沟组流纹岩分布较为广泛。色皮口地区流纹岩SiO2介于70.81%～77.62%,碱总量6.87%～9.02%,K2O/Na2O为0.74～1.04,K2O/TiO2和K2O/P2O5比值分别为10.38～18.83、72.45～242.14,A/CNK指数介于1.43～1.55,具有高硅、高铝质的特点。不相容元素K、Rb、Th、Ba富集,高场强元素Nb、Ta、Zr、Hf富集,ΣREE141.76×10-6～228.2×10-6,(La/Yb)N4.11～7.42,δEu0.27～0.50,流纹岩稀土总量较低,轻重稀土分异显著,铕负异常明显。流纹岩原始地幔标准化蛛网图显示Sr、Nb、Ta、P和Ti负异常,而Sr、P、Ti谷深,显示较强的岩浆分异作用。流纹岩的锆石LA-MC-ICP-MSU-Pb定年结果为314.0±1.1Ma(n=17,MSWD=1.6,Th/U比值在0.39～0.80之间),这表明流纹岩形成时代为晚石炭世。结合区域上前人的Sr-Nd、O和Hf同位素成果,推测区域分布的流纹岩可能来源于两个不同的源区:亏损地幔的幔源基性火成岩经过部分熔融或幔源玄武岩浆结晶分异和地壳物质部分熔融,可能代表了裂谷闭合时期构造应力场由拉张到挤压频繁转换作用的产物。The Sepikou area in Xinjiang is located in the north of the eastern section of the Bogda orogenic belt, where the upper Carboniferous Liushugou Formation rhyolites are widely present. The rhyolites in the Sepikou area have SiO2 content between 70.81% and 77.62% ; Na2O ＋ K2O content between 6.87% and 9.02% ; high K2O/TiO2 and K2O/P2O5 ratios（ values arel0.38 - 18.83 and 72.45 - 242.14, respectively）, A/CNK ratios ranging between 1.43 and 1.55, with high-Al and high-Si characteristics. The rhyolites are characterized by high content of K, Rb, Th, Ba, and HFSE （ Nb, Ta, Zr, Hf）. ∑ REE contents vary between 141.76 × 10^ -6 and 228.2 × 10^ -6 , with （La/Yb） N 4.11 - 7.42. They also display fractionated REE patterns with prominent negative Eu anomalies （ 8Eu =0.27 -0.50）. Compared with the primitive mantle, the rhyolites are depleted of Sr, Nb, Ta, P and Ti, suggesting that they have experienced strong crystallization differentiation of magma. Zircon U - Pb ages of the rhyolite are 314.0 ± 1.1 Ma （ n = 17, MSWD = 1.6, Th/U = 0.39 - 0.80） , representing the crystallizing age of the rhyolite. By comprehensive analysis of previous St, Nd, O and Hf iso- topes, the Late Carboniferous rhyolite formed in the partial melting of basic igneous rock from depleted mantle, or fractional crystallization of basaltic magma by crustal material contamination and the partial melting of crust. It probably represents the product of the frequent conversion from extension to com- pression in the rift closing period.

关 键 词：柳树沟组 地球化学 流纹岩 U—Pb年龄 新疆 

分 类 号：P597.3[天文地球—地球化学]