湘西民乐地区马底驿组-牛蹄塘组板岩类稀土元素地球化学特征及其意义

Madiyi formation-Niutitang formation slate class geochemical characteristics of rare earth elements and their significance in Minle area,western Hunan province,China

湘西民乐地区沉积了一套新元古代马底驿组-寒武纪纽芬兰世牛蹄塘组的浅变质板岩类,地层倾角为10°~20°,南东向倾向,层理发育。为了探讨该区的浅变质板岩类的原岩特征和原岩形成时大地构造环境,本文采用等离子体质谱分析仪对样品进行稀土元素分析测试。结果表明:板岩类稀土元素总量REE,轻、重稀土比和Eu,Ce的异常与沉积岩基本一致,表明了民乐地区板岩类的原岩与沉积岩近似。由ΣREE-La/Yb图解和稀土元素特征与不同大地构造背景沉积岩的稀土元素特征比较,得出变质板岩类的原岩为沉积的碎屑物质(火山喷发的玄武岩、泥岩和杂砂岩)形成沉积岩,大地构造环境为活动大陆边缘。

A set of shallow metamorphic slate type of Neoproterozoic Madiyi formation-Cambrian Niutitang formation is deposited in the Minle area,western Hunan,which is bedding development,south-east dip and dip angle of 10° ~ 20°. In order to explore original rock characteristics and formation of the tectonic environment of shallow metamorphic slate type in this area,this paper adopts the plasma mass spectrum analyzer to test the rare earth elements of the sample. The results show that slate type total REE of rare earth elements、light and heavy rare earth ratio and anomal Eu、Ce are consistent with sedimentary rock,which shows the original rock of slate type are similar to sedimentary rock. Through the Σ REE-La /Yb diagram and compared with characteristics of rare earth elements with different tectonic background of sedimentary rocks,we can draw the protolith of metamorphic slate type is depisitional clastic detritus（ volcanic eruption basalt,mudstone and greywacke）,and formation of the tectonic environment is active continental margin.