滇西澜沧黑河地区超高压变质岩中金红石微量元素特征

The Trace Element Characteristics of Rutile in Ultra-High-Pressure Metamorphic Rocks in the Heihe Region,Lancang,Western Yunnan

为研究黑河地区金红石微量元素特征及榴辉岩型金红石矿床的成矿地质条件,本文选取滇西澜沧黑河地区榴辉岩、石榴多硅白云母片岩中的金红石进行LA-ICP-MS微量元素分析。结果表明金红石微量元素呈现阶梯式三级分布特征,最富集Nb、Ta,其次是Zr、Hf,含量较少的元素有Ba、Rb、Sr、Th、REE;榴辉岩、榴闪岩类原岩属于变质基性岩类,含蓝晶石榴闪岩原岩属于玄武质凝灰岩类,石榴多硅白云母片岩类原岩属于泥质岩类;榴辉岩中金红石Nb/Ta比值均要高于其全岩Nb/Ta比值,金红石Nb、Ta含量与变质作用过程中元素在各矿物间的分配系数有关;采用金红石Zr含量温度计获得黑河地区榴辉岩的峰期变质阶段金红石形成温度为578~605℃,峰期变质作用后的退变质流体会造成金红石中Zr的再平衡。此外,黑河地区具备榴辉岩型金红石矿床形成的成矿物源、成矿作用的物理化学条件以及成矿的物质基础,有一定的找矿潜力。

In order to study the trace element characteristics of rutiles in the Heihe region and the geological conditions for the mineralization of eclogite-type rutile deposits,this study selected rutiles from eclogite and garnet phengite schist in the Heihe region of Yunnan for LA-ICP-MS trace element analysis.The results show that the trace elements in rutiles exhibit a stepped three-level distribution pattern,with Nb and Ta being the most abundant,followed by Zr and Hf.The elements with lower content include Ba,Rb,Sr,Th,and REE.The protoliths of the eclogites and amphibole eclogite type belong to metamorphic mafic rocks,while the protoliths of kyanite-bearing amphibole eclogite and garnet phengite schist belong to basaltic tuffs and argillaceous rocks,respectively.The Nb/Ta ratios of rutiles in eclogite are higher than that of the entire rocks.The Nb and Ta contents of rutiles are related to the partition coefficients of elements among various minerals during metamorphism.The formation temperature of rutiles from the peak metamorphic stage of eclogites in the Heihe area was 578~605℃,obtained by using a Zr-in-rutile thermometer.The retrograde mass flow after the peak metamorphic process resulted in a reequilibrium of Zr in the rutiles.In addition,the Heihe region possesses the ore-forming material source,physical and chemical conditions for mineralization,and material basis for the formation of eclogite-type rutile deposits,which has certain prospecting potential.