| 内蒙古贺根山蛇纹岩化流体来源的H-O-B同位素地球化学制约 |
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| 引用本文： | 龙雄志,郭锋,赵亮,章清文,吴扬名.内蒙古贺根山蛇纹岩化流体来源的H-O-B同位素地球化学制约[J].大地构造与成矿学,2017,41(3):590-603. |
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| 作者姓名： | 龙雄志 郭锋 赵亮 章清文 吴扬名 |
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| 作者单位： | 1. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640;中国科学院大学,北京100049;2. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 |
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| 基金项目： | 国家科技部973项目二级课题，国家杰出青年基金项目，广东省“特支计划”科技创新领军人才项目 |
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| 摘 要： | 对内蒙古贺根山蛇绿岩带内3个采样点的蛇纹岩样品开展了主量、微量元素和H-O-B同位素分析,以揭示其构造属性、蛇纹石化温度和流体来源。贺根山蛇纹岩具有低Al_2O_3含量(0.2%~1.3%)、高Mg~#(89~92)特征,为难熔地幔残余。蛇纹岩的U型稀土元素配分模式、相对富集LILE和亏损HFSE的微量元素地球化学特点,反映其原岩为化学成分高度亏损的俯冲带型(SSZ)超基性岩。样品的dD值相对均一(dD=-120‰~-133‰);理论计算显示,这些蛇纹岩的H同位素组成可能是蛇绿岩剥露地表后与区域大气降水发生再平衡作用的结果。贺根山蛇纹岩的d~(18)O变化在4.3‰~9.8‰之间,反映不同地点蛇纹石化的温度存在差别:其中贺根山东样品具有相对较高的d~(18)O值(d~(18)O=7.7‰~9.8‰),蛇纹石化温度为90~130℃,同时部分样品中出现碳酸盐矿物,表明蛇纹石化作用发生在近海底环境;小坝梁样品具有最低的d~(18)O值(d~(18)O=4.3‰~5.0‰),其蛇纹石化温度在205~235℃之间;贺根山南样品的d~(18)O值变化范围较大(d~(18)O=6.0‰~9.7‰),其蛇纹石化温度在90~170℃之间。3个采样点蛇纹岩的d~(11)B值也显示出一定的变化(d~(11)B=9.1‰~14.7‰),指示蛇纹石化流体来源于脱水的蚀变洋壳和海底沉积物;理论模拟和计算结果显示,这些板片流体的d~(11)B值变化在15‰~25‰之间。
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| 关 键 词： | 俯冲板片流体 H-O-B同位素组成 微量元素 蛇纹岩 内蒙古贺根山 |
H-O-B Isotopic Constraints on Fluid Origin of Serpentinization of the Hegenshan Ophiolite,Inner Mongolia |
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| LONG Xiongzhi,GUO Feng,ZHAO Liang,ZHANG Qingwen,WU Yangming.H-O-B Isotopic Constraints on Fluid Origin of Serpentinization of the Hegenshan Ophiolite,Inner Mongolia[J].Geotectonica et Metallogenia,2017,41(3):590-603. |
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| Authors: | LONG Xiongzhi GUO Feng ZHAO Liang ZHANG Qingwen WU Yangming |
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| Abstract: | We report major,trace elements and H-O-B isotopic compositions of serpentinites sampled in three localities of the Hegenshan ophiolite in Inner Mongolia,with aims to constrain the tectonic setting,alternation temperature and fluid origin of the serpentinization.The serpentinites,which are characterized by low A12O3 (0.2％-1.3％) and high Mg# (89-92),were the residual and refractory mantle peridotites after high-degree basalt extraction.They also show U-type REE patterns,enrichment in large ion lithophile elements (LILE) and depletions in high field strength elements (HFSE),reflecting their derivation from a highly depleted super-subduction zone (SSZ).The studied samples show relatively uniform δD values range from-120‰ to-133‰,and mass balance calculation suggest that these serpentinites re-equilibrated with present-day local meteoric water after exposure onto the surface.The serpeninites from the eastern and southern Hegenshan and Xiaobaliang have δ18O values of 7.7‰-9.8‰,6.0‰-9.7‰ and 4.3‰-5.0‰,respectively,corresponding to altemation temperatures of 90-130 ℃,90-170 ℃ and 205-235 ℃.Also,the occurrence of carbonate minerals in some serpeninites from the eastern Hegenshan indicates the near-seafloor serpeninization.The serpeninites in the Hegenshan also show variable δ11B values (δ11B=9.1‰-14.7‰),suggesting that serpeninization was likely caused by fluids dehydrated from the subducted slab and pelagic sediments with a δ11B range of 15‰-25‰. |
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| Keywords: | dehydration fluids of subducted slab H-O-B isotopic compositions trace element serpentinites Inner Mongolia |
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