低级变质岩在热液蚀变过程中的微量元素地球化学行为－以赣东北银山地区双桥山群为例
Geochemical behavior of trace element during hydrothermal alteration in low-metamorphic rock: a case study for Shuangqiaoshan Group in Yinshan area, northwestern Jiangxi province, China
查看参考文献16篇
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文摘
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对江西银山地区双桥山群绢云母千枚岩及其原岩的稀土及微量元素的研究表明，热液蚀变过程中它们的地球化学行为 发复杂：热液蚀变作用并不使REE淋滤降低，反而导致ΣREE较其原岩普遍升高，但岩体接触带附近蚀变围岩的ΣREEE则低于原岩。蚀变岩出现Eu亏损，ΣREE／ΣHREE值降低。它量计算显示，ΣREE总升幅中有29％～45％是由围岩质量迁移引起的表现浓缩效应，而另外的55％～71％则是流体带入了REE；在绢云母千枚岩中绢云母可能是REE的主要寄主矿物相，REE主要以吸附作用的形式固着在矿物的表面或含有可交换电价的晶体结构层（四面体层和八面体层）的层面上；参与蚀变作用的热液ΣLREE／ΣHREE值低、Eu强正异常。流体REE的带入可能是造成蚀变围岩较原岩轻重稀土比值降低的主要因素。热液蚀变作用使岩石的Eu被还原成更易活动的Eu~(2+)而活化迁出，导致蚀变岩的Eu负异常更显著；围岩蚀变作用造成Sr普遍降低，Ba显著升高，而Rb含量相对稳定，这是由其主要寄主矿物相的变化特征所致；Hf、Th、U、V、Cr、Co、Nb、Mo、Ta、Zr表现为惰性，成矿元素Cu、Pb、Zn、Ag和Sn等大量带入，Y、Sc活化迁出。 |
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其他语种文摘
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Rare earth elements and other trace elements in altered phyllite and its fresh counter part were determined in order to examine behavior of the trace elements during hydrothermal alteration in Shuangqishan group, a set of low-metamorphic rock in Yinshan polymetallic area of northwestern Jiangxi province. It is demonstrated that behavior of the trace elements during alteration were extremely complicated. The trace element characteristics are as follows: (1) Instead of being leached, REE contents were higher in the altered phyllite in a magnitude range from 8.6% to 54.8% than in their fresh counterparts, excepting samples on the contact with lower REE concentrations. Less than 45% of the increment REE contents were caused by the "condensed" effect of mass transfered of major elements such as Si, Na, Mg etc. removed from the rock, and larger than 55% of which should be responsible for the addition of REE into the rock from hydrothermal fluid that caused rock alteration. Significantly lower contents of REE in samples on the contacts of intrusion were ascribed to the dilution caused by much more higher contents of REE barren-mineral such as quartz, pyrite and sphalerite in the rock. (2) The acting hydrothermal fluid was characterized by low ΣLREE/ΣHREE ratios and in a reductive state, resulting in a less partition between LREE and HREE in altered phyllite and evident loss of Eu that caused by Eu~(3+) was reduced into more mobile Eu~(2+) and was removed from phyllite. Dissolution of feldspars may also be responsible for part of ΣLREE/ΣHREE ratio decrease in altered rock by causing selective mobility of LREE and removed out. (3) LIL elements such as Rb, Su, Ba show different behavior due to their hosting phases changed in different ways. Hf, Th, U, V, Cr, Co, Nb, Mo, Ta and Zr show immobility during hydrothermal alteration. Y and Sc were carried off while the ore-forming elements such as Cu, Pb, Zn, Ag and Sn were introduced into altered phyllite by hydrothermal fluid during hydrothermal alteration. |
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来源
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岩石学报
,2002,18(1):100-108 【核心库】
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关键词
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低级变质岩
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热液蚀变作用
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微量元素地球化学行为
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银山地区
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地址
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中科院贵阳地球化学研究所, 地球深部物质与流体作用地球化学实验室, 贵阳, 550002
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语种
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中文 |
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文献类型
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研究性论文 |
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ISSN
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1000-0569 |
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学科
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地质学 |
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基金
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国家“九五”攀登计划项目
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国家自然科学基金国家杰出青年科学基金
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文献收藏号
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CSCD:1151381
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