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西藏永珠—纳木湖蛇绿岩地球化学特征及其构造环境初探
引用本文:杨日红,李才,迟效国,王天武.西藏永珠—纳木湖蛇绿岩地球化学特征及其构造环境初探[J].现代地质,2003,17(1):14-19.
作者姓名:杨日红  李才  迟效国  王天武
作者单位:1. 中国国土资源航空物探遥感中心,北京,100083
2. 吉林大学,地球科学系,吉林,长春,130061
基金项目:国土资源部西藏申扎县幅1∶25万区域地质调查项目(20001300009141)。
摘    要:西藏永珠—纳木湖蛇绿岩中的变质橄榄岩从超镁铁质岩到镁铁质岩均表现出高镁,其玄武岩、辉长岩的TiO2含量较低,表现出非大洋中脊玄武岩和洋岛玄武岩的特征。微量元素、大离子亲石元素相对富集,玄武岩的Nb、Ta亏损,显示其在产出时受到俯冲作用的影响,具有岛弧玄武岩的特点,但Th的高度富集和无Zr、Hf负异常说明它又不同于岛弧玄武岩。稀土元素含量较低,在球粒陨石标准化稀土分布模式图上玄武岩为平坦型,无Eu异常,显示其具有原生岩浆成分的特点;辉长岩的稀土配分模式也为平坦型,但有Eu正异常。通过与典型地区作对比和应用构造环境判别图解,判定出该区蛇绿岩的形成环境为弧后盆地。

关 键 词:蛇绿岩  岩石组合  地球化学特征  构造环境  西藏
文章编号:1000-8527(2003)01-0014-06
修稿时间:2002年9月9日

THE PRIMARY STUDY OF GEOCHEMICAL CHARACTERISTICS AND TECTONIC SETTING OF OPHIOLITE IN YONGZHU-NAMUHU,TIBET
Abstract:From the analysis of the major elements of ophiolite in Yongzhu Namuhu of Tibet, the characteristics of its metamorphic peridotite are high Mg content. And the characteristic of its basalt and gabbro is not the one of Mid Ocean Ridge Basalt (MORB) and Island Arc Basalt (IAB), for the percentage of TiO2 is very low, no more than 15%. According to the trace elements in the ophiolite, on one hand, the basalt shows the same characteristic as the Island Arc Basalt, for the depletion elements of Nb and Ta. On the other hand, the characteristic of basalt is not the same as the IAB's, for its high enrichment of Th and the non depletion of Zr, Hf. The ∑REE of the ophiolite is low. Meanwhile, according to the REE distribution patterns, the basalt is of the characteristic of proto magma for its evenness form with no Eu anomaly. And the gabbro shows evenness form with Eu positive anomaly. It is concluded that the ophiolite of Yongzhu Namuhu tectonic setting is formed in back arc basin by the comparison with the ophiolite of typical areas and discrimination diagrams of the tectonic setting.
Keywords:ophiolite  rock assemblage  geochemical characteristic  tectonic setting  Tibet
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