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新疆西准噶尔木哈塔依蛇绿混杂岩年代学和地球化学研究及构造意义

ISSN号：1000-3657
期刊名称：《中国地质》
时间：0
分类：P581[天文地球—岩石学;天文地球—地质学] P597.3[天文地球—地球化学;天文地球—地质学]
作者机构：[1]大陆构造与动力学国家重点实验室地幔研究中心,中国地质科学院地质研究所,北京100037, [2]中国地质大学地球科学与资源学院,北京100083, [3]中国地质大学地球科学学院,湖北武汉430074
相关基金：国家专项项目（201011034）; 国家自然科学基金创新研究群体项目（41221061）联合资助致谢：锆石U-Pb测年和Hf同位素分析在天津地调中心张建工程师的帮助下完成,电子探针分析得到了郭虎工程师的协助,实验过程先后得到了周文达、陈梅、张财、陈艳虹等协助,在此一并感谢!

作者：田亚洲[1], 杨经绥[1], 王云鹏[2], 赵一珏[2], 连东洋[3], 张岚[2], 李源[1]

关键词：地球化学, 锆石U-PB年龄, HF同位素, 木哈塔依蛇绿混杂岩, 西准噶尔, 新疆, geochemistry, zircon U-Pb, Hf isotope, Muhatayi ophiolitic mélange, West Junggar, Xinjiang

中文摘要：

木哈塔依蛇绿混杂岩位于新疆西准噶尔达拉布特蛇绿岩带北东端,蛇绿岩组合包括蛇纹石化及石英菱镁岩化方辉橄榄岩、玄武岩和硅质岩,蛇绿岩中侵入有辉长岩脉。对蛇绿岩开展了详细的岩相学、岩石地球化学、锆石UPb年代学和Hf同位素研究。玄武岩和辉长岩均为低钾拉斑玄武岩系列,两者同时具有轻稀土富集和弱亏损的EMORB和N-MORB的配分曲线,微量元素具有Ba、U、K、La、Ce等LILE相对富集,Nb、Ta、Th等HFSE相对亏损的特征,结合玄武岩中相对稳定的微量元素和氧化物构造判别图解,认为蛇绿岩形成于弧后盆地。玄武岩LA-ICPMS锆石U-Pb同位素年龄为（392.5）±2.9 Ma（n=26,MSWD=1.3）,代表蛇绿岩形成年龄。玄武岩锆石εHf（t）值为＋12.2～＋15.1,Hf同位素地幔模式年龄t（DM）（407～543 Ma）与锆石形成年龄相近,指示玄武岩直接来源于亏损地幔,且没有遭受地壳物质的明显混染。地幔岩铬尖晶石化学成分和玄武岩Dy/Yb-La/Yb图解表明,地幔橄榄岩可能为亏损的尖晶石二辉橄榄岩发生25%～30%部分熔融的残余,而熔出的基性熔体为玄武岩和辉长岩的母岩浆。综合研究认为,达拉布特蛇绿岩所代表的西准噶尔洋盆为准噶尔洋北西俯冲形成的弧后盆地,洋盆在中志留世就已经存在并开始扩张,直到早石炭世洋盆依然存在,晚石炭世洋盆进入俯冲消减和闭合阶段。

英文摘要：

Located in the northeast Darbute ophiolitic mélange, West Junggar, Xinjiang, the Muhatayi ophiolitic mélange consists mainly of harzburgite with serpentinization and silica- carbonate alteration, basalt and chert, together with some intrusive gabbro veins. In this study, petrographic and geochemical analysis, U- Pb dating and Hf isotope study were conducted for ophiolitic mélange. Both of basalt and gabbro in ophiolitic mélange belong to low-potassium tholeiitic series, display typical characteristics of E-MORB and N-MORB, and are enriched in LILE（Ba, U, K, La, Ce） and depleted in HFSE（Nb, Ta,Th）. In combination with the discrimination diagrams of immobile trace elements and oxides, the authors hold that the Muhatayi ophiolitic mélange was produced in an arc-basin setting. The LA-ICP-MS U-Pb isotope dating of zircons from basalt yielded an age of（392.5 ± 2.9） Ma（n=26,MSWD=1.3）, which represents the age of ophiolitic mélange. εHf（t） values of zircons range from ＋12.2 to ＋15.1 and t（DM）（407-543Ma）values are close to the ages of zircons, which indicates that the basaltic magmas were derived from depleted mantle without crustal contamination. The chemical composition of Cr-spinel of harzburgite and the Dy/Yb versus La/Yb of basalt reveal that the harzburgite was the residual after the 25%- 30% partial melting of depleted spinel- lherzolite, the mafic melt was the parental magmas of basalt and gabbro. It is thus considered that the west Junggar Basin represented by Darbute ophiolitic mélange was developed in an arc- basin setting resulting from the northwestward subduction of Junggar Ocean,the west Junggar Ocean was spread before Middle Silurian and remained existent in early Carboniferous, and then the oceanic basin experienced the stage of subdution and closure.