| 西藏班公湖-怒江缝合带中西段康穷蛇纹岩的岩石学、地球化学特征及其构造意义 |
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| 引用本文： | 许伟,李才,吴彦旺,徐梦婧,范建军,江庆源,彭虎.西藏班公湖-怒江缝合带中西段康穷蛇纹岩的岩石学、地球化学特征及其构造意义[J].地质通报,2015,34(8):1401-1412. |
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| 作者姓名： | 许伟 李才 吴彦旺 徐梦婧 范建军 江庆源 彭虎 |
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| 作者单位： | 1.吉林大学地球科学学院，吉林长春130061；2.中国国土资源航空物探遥感中心，北京100083；
3.天津城建大学地质与测绘学院，天津300384 |
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| 基金项目： | 国家自然科学基金项目（批准号：41272240、41072166、41273047）和中国地质调查局项目（编号：1212011221093、12120113036700） |
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| 摘 要： | 康穷蛇纹岩出露于班公湖-怒江缝合带的中西段,是康穷蛇绿混杂岩的超基性岩石端元。依据全岩地球化学元素含量,可将康穷蛇纹岩划分为A组和B组2种。两者均富集大离子亲石元素(Rb、Cs)和高场强元素(U、Nb)。经估算,A组蛇纹岩原岩是原始地幔经过10%~17%部分熔融的地幔残留,B组蛇纹岩原岩经历过更高程度的部分熔融(17%~23%),表明康穷蛇纹岩原岩至少经历过两阶段的部分熔融。初步研究认为,A组蛇纹岩原岩是洋内俯冲初始阶段上涌软流圈地幔部分熔融的地幔残留,受类MOR型熔体交代作用而仍然亏损轻稀土元素(LREE),却富集U和Nb,属类MOR型地幔橄榄岩;B组蛇纹岩原岩是A组蛇纹岩原岩在洋内俯冲带环境再熔融的产物,受玻安质熔体交代作用而相对富集轻稀土元素,属弧前地幔橄榄岩。两者均发生蛇纹石化作用而转变成蛇纹岩,最终因大洋碰撞闭合而残存于缝合带内,是班公湖-怒江新特提斯洋洋内俯冲演化阶段的岩石记录。
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| 关 键 词： | 蛇纹岩 地球化学 蛇绿岩 洋内俯冲 班公湖-怒江新特提斯洋 |
Petrological and geochemical characteristics of Kangqiong serpentinites in the central- western part of Bangong- Nujiang suture zone, Tibet |
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| XU Wei,LI Cai,WU Yanwang,XU Mengjing,FAN Jianjun,JIANG Qingyuan,PENG Hu.Petrological and geochemical characteristics of Kangqiong serpentinites in the central- western part of Bangong- Nujiang suture zone, Tibet[J].Geologcal Bulletin OF China,2015,34(8):1401-1412. |
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| Authors: | XU Wei LI Cai WU Yanwang XU Mengjing FAN Jianjun JIANG Qingyuan PENG Hu |
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| Abstract: | Kangqiong serpentinites, exposed in the central-western part of Bangong-Nujiang suture zone, constitute the ultrabasic end member of Kangqiong ophiolitic mélange. Serpentinites in group A have relatively high Al2O3 (4.23%) and CaO (3.48%) contents, relatively depleted LREEs, their trace element normalized partition curves are similar to those of the global abyssal peridotites, whereas serpentinites in group B have lower Al2O3 (0.61%) and CaO (0.27%) values and slightly more enriched LREEs with negative Eu and Ce anomalies, and their trace element normalized partition curves resemble those of Izu-Bonin-Mariana forearc mantle peridotites, with both of them enriched in LILE (Rb, Cs) and HFSE (U, Nb). Estimation reveals that protoliths of group A were the mantle residue from partial melting of asthenospheric mantle, and protoliths of group B underwent higher-degree partial melting, indicating that they at least have experienced two stages of partial melting. It is preliminarily held that protoliths of group A were the mantle residue from partial melting of asthenospheric mantle in the forearc environment, characterized by depletion of LREE but enrichment of U and Nb because of MOR-like melt-rock interaction, and that protoliths of group B resulted from partial re-melting of group A in the intra-ocean subduction zone and became more reluctant to melting and more enriched in LREE and HFSE (U, Nb) because of boninitic melt-rock interaction, thus belonging to forearc mantle peridotites. Both protoliths of group A and group B transformed into serpentinites resulting from serpentinization, and eventually remained in the suture zone while the ancient ocean collided and closed. They are thus the rock records of intra-ocean subduction of the Bangong-Nujiang Neo-Tethys Ocean. |
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| Keywords: | serpentinites geochemistry ophiolite Intra-ocean Subduction Bangong-Nujiang Neo-Tethys Ocean |
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