榴辉岩退变质过程中的微量元素地球化学行为:对CCSD主孔退变质榴辉岩的研究  

Geochemical behavior of trace elements during retrograde metamorphism of eclogites: Study on the retrograde eclogites from the CCSD main hole.

作　　者：张斌辉[1] 刘勇胜[1] 宗克清[1] 高山[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《岩石学报》2006年第7期1833-1844,共12页Acta Petrologica Sinica

基　　金：本研究受国家重点基础研究发展规划项目(2003CB716501);教育部长江学者和创新团队发展计划(IRT0441);中国地质大学地质过程与矿产资源国家重点实验室(GPMR0511);西北大学大陆动力学国家重点实验室基金共同资助。

摘　　要：对中国大陆科学钻探工程主孔榴辉岩退变质过程中的微量元素地球化学行为进行了研究。对退变质程度连续变化样品的不同部分的对比研究表明,流体作用下的退变质过程中大离子亲石元素(Cs、Rb、Ba、Sr、K、Th、U)和轻稀土元素表现出较大的活动性,重稀土元素和高场强元素变化相对较小。退变质后大离子亲石元素的显著增加和高场强元素、重稀土元素的轻微变化(甚至相对降低),表明与退变质作用有关的流体中的络阴离子含量很少,并不富集高场强元素和重稀土元素。退变质后总体上表现出的Si、大离子亲石元素和轻稀土元素的明显变化,表明外来流体参与了榴辉岩的退变质过程,带入和带出了一些元素。结合榴辉岩中单矿物微量元素组成以及前人对DMineral/Fluid的研究成果,对流体-榴辉岩作用形成的退变质分带(富石英条带→角闪岩→退变质榴辉岩→新鲜榴辉岩)的微量元素组成变化进行了详细研究。结果表明在流体作用下的榴辉岩退变质过程中,大离子亲石元素、轻稀土元素和高场强元素含量的变化除了受退变质流体性质的影响外,更大程度上取决于退变质过程中的矿物相(尤其是副矿物)的变化。Retrograde eclogites from main hole of the Chinese Continental Scientific Drilling Project （CCSD） have been studied. To examine the trace element geochemical behavior during retrograde metamorphism, different sections from amphibolite to retrograde eclogite of samples were analyzed by ICP-MS. The results indicate that large ion lithophile elements （LILE） （ Cs, Rb, Ba, Sr, K, Th, U） and light rare earth elements （LREE） show significant and complicated variations during retrograde metamorphism. However, heavy rare earth elements （HREE） and high field strength elements （HFSE） show little variations comparing with LREE and LILE. The decoupling variations of LILE, LREE and HFSE, HREE suggest that fluids associated with retrograde metamorphism contained little anionic complex, and thus were not enriched in HFSE and HREE. On the other hand, the significant variations of Si, LILE and LREE suggest that external fluids were involved in the retrograde metamorphism. Combining the trace element compositions of minerals in eclogites and D^Mineral/Fluid, the spatial variations of trace elements of retrograde eclogite associated with fluid-eclogite interaction （quartz-rich layer-amphibolite layer-retrograde eclogite layer-fresh eclogite layer） suggest that variations of LILE, LREE and HFSE during retrograde metamorphism are not only affected by the nature of fluids, but also significantly controlled by mineral phase changing （especially accessory minerals）.

关 键 词：中国大陆科学钻探工程 榴辉岩 退变质作用 微量元素地球化学行为 

分 类 号：P588.348[天文地球—岩石学] P595[天文地球—地质学]