东天山哈尔里克山区二叠纪高钾钙碱性花岗岩成因及地质意义  

Petrogenesis and geological implications of the Permian high-K calc-alkaline granites in Harlik Mountains of eastern Tianshan, NW China

作　　者：汪传胜[1,2,3] 顾连兴[1,3] 张遵忠[1,3] 吴昌志[1] 唐俊华[1,3] 汤晓茜[1] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室南京大学地球科学系,南京210093 [2]西北大学大陆动力学国家重点实验室,西安710069 [3]江苏省有色金属华东地质勘查局,南京210007

出　　处：《岩石学报》2009年第6期1499-1511,共13页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2007CB411301-4; 2001CB409802);国家自然科学基金项目(40472042; 40672040; 40603008);西北大学大陆动力学国家重点实验室开放课题基金资助(06LCD02)资助

摘　　要：本文从岩石学、地球化学和同位素等方面讨论东天山克拉麦里-哈尔里克岛弧东段八大石和小铺东两个岩体的特征和成因。八大石岩体和小铺东岩体主要为二长花岗岩,SiO_2含量分别为61.92%～74.40%和69.17%～74.92%,K_2O+Na_2O的含量分别为6.50%～8.32%和7.74%～8.14%,绝大部分岩石具有高钾钙碱性花岗岩特征;∑REE分别为105×10^(-6)～210×10^(-6)和100×10^(-6)～172×10^(-6),(La/Yb)_(CN)分别为4.1～8.9和9.1～15.3,配分模式右倾,δEu分别为0.40～0.93和0.59～0.80,为中-低负异常;两个岩体均富Rb、Ba等大离子亲石元素和Th、U、Hf、Zr等高场强元素,而贫Ta、Nb、Sr、Ti等。通过LA-ICP-MS分析得到八大石岩体中锆石^(206)Pb/^(238)U加权平均年龄为298±2Ma,表明岩体形成于早二叠纪,计算得到八大石和小铺东岩体的模式年龄t_(DM)分别为944Ma和648Ma;八大石和小铺东岩体的ε_(Nd)(t)分别为+3.06和+4.47,(^(87)Sdr/^(86)Sr)_i分别为0.70475和0.70384,表现出高ε_(Nd)(t)低(^(87)Sr/^(86)Sr)_i。综上所述,认为哈尔里克高钾钙碱性花岗岩可能为碰撞后挤压-伸展转折阶段的产物,主要由来自新生地壳的中钾钙碱性岩浆经过结晶分异作用而成。Based upon petrologic, geochemical and isotopic investigations, this paper expounds genesis of the. Badashi and Xiaopudong plutons in the eastern part of the Kerameili-Harlik volcanic-arc belt of eastern Tianshan. The Badashi and Xiaopudong, plutons are mainly composed of monzogranites with SiO2 of 61.92% similar to 74.40% and 69.17% similar to 74.92%, K2O + Na2O of 6.50% similar to 8.32% and 7.74% similar to 8.14%, respectively. SiO2 and K2O values of most samples are plotted in the area of high-K calc-alkaline granites. These two plutons are characterized by REE of 105 x 10(-6) similar to 210 x 10(-6) and 100 x 10(-6) similar to 172 x 10(-6) (La/Yb)(CS) of 4.1 similar to 9.0 and 9.1 similar to 15.3, respectively, but consistently show right-inclined distribution patterns. They show weakly negative Eu anomalies with delta Eu being 0.40 similar to 0.93 and 0.59 similar to 0.80, respectively. These two plutons are enriched in Rb, Ba (LILE) and Th, U, Hf, Zr (HFSE), and depleted in Ta, Nb, Sr, Ti, etc. Zircon LA-ICP-MS U-Pb isotope determination gave 298 +/- 2Ma for the Badashi pluton, indicating their Early-Permian emplacement, model ages (t(DM)) are calculated to be 944Ma and 648Ma for the Badashi and Xiaopudong plutons, respectively. They are higher in epsilon(Nd) (t) (+ 3.06 and + 4.47) and lower in (Sr-87/Sr-86)(i) (0.70475 and 0.70384). It is suggested that these high-K calc-alkaline granites in the Harlik region were emplaced hiring post-collisional conversion from compression to extension, and were derived as a result of fractional crystallization of medium-K calc-alkaline magmas from juvenile crustal sources.

关 键 词：高钾钙碱性花岗岩 钙碱性 后碰撞 底侵 东天山 新疆 

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