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地质科学  2004, Vol. Issue (3): 388-406    DOI:
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藏东南雅鲁藏布蛇绿混杂岩带的物质组成及形成环境
耿全如1, 潘桂棠2, 郑来林2, 孙志明2, 欧春生3, 董翰3
1. 中国地质大学地球科学学院 武汉 430074;
2. 国土资源部成都地质矿产研究所 成都 610082;
3. 甘肃省地质矿产局地质勘查院 兰州 730050
PETROLOGICAL CHARACTERISTICS AND ORIGINAL SETTINGS OF THE YARLUNG TSANGPO OPHIOLITIC MLANGE IN NAMCHE BARWA,SE TIBET
Geng Quanru1, Pan Guitang2, Zheng Lailin2, Sun Zhiming2, Ou Chunsheng3, Dong Han3
1. Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074;
2. Chengdu Institute of Geology and Mineral Resources, Ministry of Land and Resources, Chengdu 610082;
3. Geological Survey, Bureau of Geology and Mineral Resources of Gansu Province, Lanzhou 730050
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摘要 雅鲁藏布蛇绿混杂岩带位于藏东南南迦巴瓦峰地区(喜马拉雅东构造结),呈弧形大致沿雅鲁藏布江分布,出露宽度2~10km。带内岩石变质、变形强烈,按产状可分为两大类:基质和岩块(片)。岩块(片)包括蛇绿岩套中的超镁铁岩、辉绿岩墙和辉长岩,石英(片)岩,大理岩和两侧老基底片麻岩等。岩块(片)大小不一,大的延伸可>50km,小的仅约0.5m;基质是塑性变形十分强烈的绢云母石英片岩、二云母石英片岩、绿片岩等岩石组合。变质玄武岩岩石地球化学特征表明,该蛇绿混杂岩带可能由形成环境不同的“碎片”组成,包括弧前扩张带、岛弧、弧后盆地及洋岛等环境,是典型的消减带环境的蛇绿岩(SSZ)。初步的同位素年代学测试结果,说明蛇绿岩可能在200Ma前形成,比原认为距今110~120Ma要早得多,这一结果与该带其它地段的研究成果相似。
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耿全如
潘桂棠
郑来林
孙志明
欧春生
董翰
关键词雅鲁藏布蛇绿混杂岩带   南迦巴瓦   空间展布   物质组成   形成环境     
Abstract: Recently, geologic mapping with a scale of 1:250000 and a series of special works on the regional geology of the Eastern Himalayan Syntaxis clarified the spatial distribution, petrologic composition and structures of the Indus-Yarlung Tsangpo suture in SE Tibet, where was also known for the world-deepest canyon. It was a typical ophiolitic mélange roughly along the canyon with width of 2~10 km. The major components could be divided into rock blocks and matrix. The blocks were basically from the ophiolite suite including ultramafic mafic rocks, diabase, gabbro, quartz schist, marble and exotic gneiss blocks from the Namche Barwa Formation, which could be longer than 50 km or smaller than 0.5 m. Matrix was composed of strongly deformed mica schists and green schists. The petrological studies showed that the metamorphic basalts were formed in varied settings: near island arc in back-arc basin, fore-arc rift and inner ocean volcanic arc. Some meta-basalts from the eastern margin of the curved ophiolitic belt (Jiaresa to Pangxin) had much higher contents of Si and Mg and lower HFSE and Ti than typical MORB, which were similar to boninite and indicated their original tectonic setting in fore arc accretionary wedge. More REE and trace element analysis suggested that the meta basalts near Yigongbai and Maniweng could originated on island arc and the region between Pailong-Zhaqu-Baila and Gandai could be back arc basin by meta basalt petrologic analyzing. It was concluded that the ophiolite mélange in this belt was composed of "fragments" formed in different environments: fore arc accretionary wedge, island arc, back arc basin and even oceanic island, which was a typical SSZ-type ophiolite. The isotopic dating indicated that the oceanic crust could be formed about 200 Ma ago, much earlier than that of previously idea (110~120 Ma), which was further supported by geological survey in the adjacent regions.
Key wordsThe Yarlung Tsangpo ophiolitic mélange belt   Namche Barwa   Spatial distribution   Petrologic characteristics   Genetic settings   
收稿日期: 2003-06-02;
基金资助:国土资源大调查项目(1:25万墨脱幅区域地质调查,编号:H46C003004)和973项目(印度与亚洲大陆主碰撞带成矿作用,编号:2002CB412609)的部分成果.
引用本文:   
耿全如,潘桂棠,郑来林等. 2004, 藏东南雅鲁藏布蛇绿混杂岩带的物质组成及形成环境. 地质科学, (3): 388-406.
Geng Quanru,Pan Guitang,Zheng Lailin et al. PETROLOGICAL CHARACTERISTICS AND ORIGINAL SETTINGS OF THE YARLUNG TSANGPO OPHIOLITIC MLANGE IN NAMCHE BARWA,SE TIBET[J]. Chinese Journal of Geology, 2004, (3): 388-406.
 
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[2] 钱青, 张旗, 孙晓猛, 王岳明. 北祁连老虎山玄武岩和硅岩的地球化学特征及形成环境[J]. 地质科学, 2001, (4): 444-453.
[3] 傅启龙, 沙庆安. 昌黎海岸风成沙丘砂组构特征及其与海滩砂的比较[J]. 地质科学, 1993, (1): 52-60.
 
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