川东北地区下寒武统龙王庙组白云岩成因分析

通过剖面实测、薄片鉴定、阴极发光分析和地球化学分析，对川东北地区下寒武统龙王庙组白云岩成因进行了研究。研究结果表明:研究区龙王庙组自下而上发育灰岩—过渡岩性—白云岩，以颗粒结构为主，白云石主要为泥—粉晶，呈它形—半自形晶，阴极发光呈昏暗光—暗红光。样品的MgO与CaO呈负相关，白云岩Mg2+/Ca2+较低，高Na含量，低Sr、Fe、Mn含量，白云石有序度较低，各岩性稀土元素配分曲线平行一致分布，δCe无异常，δEu负异常，灰岩δ13C偏正、δ18O处于同期海水内，白云岩δ13C、δ18O偏正，87Sr/86Sr高于同期海水值。结合区域地质背景、岩石学特征和地球化学分析结果，研究区白云石化流体为高盐度蒸发海水，研究区白云岩为渗透回流白云石化作用形成。

Genesis of Dolomite in the Lower Cambrian Longwangmiao Formation,Northeastern Sichuan Basin

Based on measurement of field outcrops， microscopic thin section identification， cathodoluminescence analysis and geochemical analysis， this paper systematically studied the genesis of dolomite in the lower Cambrian Longwangmiao Formation， northeastern Sichuan Basin. It was found that limestone?transitional lithology?dolomite was developed from bottom to top in the study area， and the rocks have a predominantly grainy texture. The dolomite is mainly subhedral?xenotopic micritic to powder crystalline， and exhibits dim， dark?red luminescence. The MgO and CaO contents of the samples are negatively correlated. The Mg2+/Ca2+ ratio， the Sr， Fe and Mn contents and the order degree of the dolomite are relatively low， but the Na content is relatively high. The distribution curves of rare earth elements （REE） in each lithology are parallel and uniform， and it shows δEu anomalies but no δCe anomalies. The δ18O value of the limestone is consistent with that of coeval seawater. The δ13C and δ18O values of the dolomite and the δ13C values of the limestone are slightly higher than for coeval seawater. The 87Sr/86Sr ratio of the dolomite is higher than for coeval seawater. Combined with the regional geological background， petrological characteristics and geochemical analysis results， it is considered that the dolomitization fluid in the study area was highly saline evaporating seawater. The dolomite in the study area was formed by seepage?reflux dolomitization.