塔里木盆地柯坪-巴楚地区早古生代白云岩类型及微量元素地球化学特征  

DOLOMITE TYPES AND TRACE ELEMENT GEOCHEMISTRY OF THE EARLY PALEOZOIC STRATA IN THE KEPING-BACHU AREA,TARIM BASIN

作　　者：王旭[1,2] 沈建伟[1] 陈代钊[3] 杨红强[1,2] 王月[1,2] 

机构地区：[1]中国科学院边缘海地质重点实验室,中国科学院南海海洋研究所,广东广州510301 [2]中国科学院研究生院,北京100049 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《矿物岩石》2011年第2期23-32,共10页Mineralogy and Petrology

基　　金：国家自然科学基金(No:40872078);中国科学院南海海洋研究所知识创新工程领域前沿项目(No.LYQY200806)

摘　　要：通过对柯平-巴楚早古生代碳酸盐岩露头样品的染色薄片鉴定、阴极发光研究和微量元素测定及分析,根据其结构成因特征把研究区白云岩分为8种类型:(1)微-粉晶白云石;(2)具原生灰岩残余结构白云石;(3)细晶直面自形-半自形漂浮基质白云石;(4)细晶直面半自形-自形白云石;(5)中-粗晶曲面他形白云石;(6)中晶直面自形-半自形白云石胶结物;(7)粗晶曲面鞍形白云石基质,和(8)粗晶曲面鞍形白云石胶结物。样品微量元素地球化学的总体特征是轻稀土富集,重稀土亏损,不同样品的特征变化元素不同。鞍形白云石Eu正异常最高说明受到热液作用的影响。方解石的Ce/Ce*的值大于1,说明受到后期陆源碎屑影响比较大,而白云岩的Ce/Ce*的值都小于1,说明是幔源成因的。(La/Ce)N和(La/Yb)N比值亦进一步证明上述结论。鞍形白云石的Sr含量较低,Ba元素含量高,说明在成岩流体作用过程中Sr丢失,Ba富集说明是热液成因的鞍形白云岩。样品Sr/Ba比值均大于1,说明受到不同程度热液作用影响。U/Th比值也证明受到不同程度的热液改造。Through the analysis and determination of stained thin sections,observation of cathodoluminescence,and testing of trace elements for the early Paleozoic carbonate in the Tarim basin,eight types of dolomites with different textural genesis are recognized.They are micritic-calcisiltic dolomite,dolomite with relict texture of limestone,fine planar euhedral-subeuhedral floating matrix dolomite,fine euhedral-subeuhedral dolomite,medium-coarse nonplanar anhedral dolomite,medium planar euhedral-subeuhedral dolomite cement,coarse nonplanar saddle matrix dolomite,and coarse nonplanar saddle dolomite cement respectively.Analysis of trace element geochemistry reveals that these samples are rich in light REE,deficit in heavy REE,with negative Eu anomaly.Samples with relative high trace elements are of great variability,and different samples are of different variable elements.Saddle dolomite is characterized by high Eu positive anomaly,indicating hydrothermal influence.The Ce/Ce＊ value of calcite is larger than 1,indicating influence of detrital material of terrigenous origin.However,the Ce/Ce＊ value of dolomite is less than 1,demonstrating mantle origin,which can be further evidenced by the values of（La/Ce）N and（La/Yb）N.Saddle dolomite is characterized by low Sr and high Ba content,the former illustrates the diagenetic process and the latter indicates the hydrothermal origin.The Sr/Ba ratios of all samples are larger than 1,indicating the hydrothermal influences with variable extent,which is approved by the ratios of U/Th of all samples.

关 键 词：白云岩 微量元素 稀土元素 早古生代 塔里木盆地 

分 类 号：P581[天文地球—岩石学]