新疆谢米斯台地区乌兰萨拉岩体地球化学、年代学及全岩Sr-Nd和锆石Hf同位素研究  

Geochemistry,geochronology,whole rock Sr-Nd and zircon Hf isotopes of the Wulansala granite pluton in Xiemisitai area,Xinjiang

作　　者：王敏[1] 王居里[1] 胡洋[1] 王建其[1] WANG Min, WANG JuLi , HU Yang , WANG JianQi(State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi＇an 710069, Chin)

机构地区：[1]大陆动力学国家重点实验室西北大学地质学系,西安710069

出　　处：《岩石学报》2018年第3期618-636,共19页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41572057);"十二五"国家科技支撑计划项目(2011BAB06B01-03)联合资助

摘　　要：谢米斯台地区位于新疆西准噶尔北部,该地区中酸性岩浆活动强烈。本文对谢米斯台地区乌兰萨拉岩体进行了地质、地球化学、年代学及全岩Sr-Nd和锆石Hf同位素研究。结果表明,乌兰萨拉岩体是一个由碱长花岗岩和花岗闪长岩组成的复式岩体。碱长花岗岩形成时代为晚志留世(422.7±2.0Ma),岩石高硅、富碱,属于准铝质-弱过铝质高钾钙碱性花岗岩;球粒陨石标准化配分模式图显示"V"字型配分样式,Eu负异常强烈,相对富集Ga、K、Rb、Th、U和Pb,亏损Ba、Sr、P、Ti、Cr和Ni等;岩石具有低(^(87)Sr/^(86)Sr)i值(0.7017~0.7038),正的ε_(Nd)(t)值(+4.49^+6.58)和锆石ε_(Hf)(t)值(+10.0^+14.2),Hf同位素模式年龄(t_(DM2))为500~771Ma。花岗闪长岩形成时代为早泥盆世(411.7±1.7Ma),属于准铝质,高钾钙碱性-钾玄岩系列花岗岩;球粒陨石标准化配分模式图显示右倾型配分样式,无明显Eu异常,相对富集LREE、LILE(Rb、Ba、K)、Th、U和Pb,亏损Nb、Ta、P和Ti等;岩石具有低的(^(87)Sr/^(86)Sr)i值(0.7041~0.7046),正的ε_(Nd)(t)值(+1.66^+3.87)和锆石ε_(Hf)(t)值(+4.4^+13.9),Hf同位素模式年龄(t_(DM2))为516~1120Ma,岩石Nd同位素和锆石Hf同位素出现一定程度的解耦。综合研究认为,乌兰萨拉岩体碱长花岗岩属A_2型花岗岩,花岗闪长岩属I型花岗岩,两者都是由新生下地壳发生部分熔融而形成,前者经历了一定程度的分离结晶作用,后者受到亏损玄武质岩浆(俯冲板片脱水交代地幔楔产生的上涌岩浆)的底侵,它们均形成于陆缘弧环境。Xiemisitai district is located in the northern part of the West Junggar, Xinjiang, where granitoid intrusions are widely distributed. We carried out combined studies of geology, geochemistry, geochronology and whole rock Sr-Nd and zircon Hf isotopes upon the Wulansala granite pluton in this area. The result shows that the Wulansala pluton is a composite intrusion composed of alkali-feldspar granite and granodiorite. The alkali-feldspar granite belongs to metaluminous-weakly peraluminous high-K calc-alkaline granite and characterized by high silicon and enrich of alkali, and formed in Late Silurian （422.7±2.0Ma）. The chondrite-normalized REE patterns of the alkali-feldspar granite indicates a ＂V＂ type diagram with a strong negative Eu anomaly. It is relatively enriched in Ga, K, Rb, Th, U and Pb but poor in Ba, Sr, P, Ti, Cr as well as Ni, etc. （^87Sr/^86Sr）i and εNd（t） values of alkali-feldspar granite are 0.7017-0.7038 and ＋4.49-＋6.58, respectively, and zircon εHf（t） values vary from ＋9.7 to ＋13.9, and Hf model ages （tDM2） are 500-771Ma. The granodiorite belongs to metaluminous high-K calc-alkaline to shoshonitic granite, and formed in Early Devonian （411.7±1.7Ma）. The chondrite-normalized REE patterns indicates right-incline type with no obvious Eu anomaly. It is relatively enriched in LREE, LILE （Rb, Ba, K）, Th, U and Pb but poor in Nb, Ta, P as well as Ti, etc. （^87Sr/^86Sr）i and εNd（t） values of granodiorite are 0.7041-0.7046 and ＋1.66-＋3.87, respectively, and zircon εHf（t） values vary from ＋4.0 to ＋15.1, and Hf model ages （tDM2） are 516-1120Ma, showing that Nd and Hf isotopic compositions are decoupled. In conclusion, the alkali-feldspar granite belongs to the A2-type granite and the granodiorite granite is I-type granite. They are formed by partial melting of the juvenile lower crust. The alkali-feldspar granite has experienced fractional crystallization, and the granodiorite is generated by underplating of depleted basaltic magma （the

关 键 词：I型和A型花岗岩 晚志留世 早泥盆世 陆缘弧 谢米斯台 新疆 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]