川东南地区娄山关群白云岩稀土元素特征及其意义  

Characteristics and indications of rare earth elements in dolomite of the Cambrian Loushanguan Group,SE Sichuan Basin

作　　者：江文剑[1] 侯明才[1,2] 邢凤存[1,2] 徐胜林[1] 林良彪[1,2] 

机构地区：[1] 成都理工大学沉积地质研究院,四川成都610059 [2]成都理工大学油气藏地质与开发工程国家重点实验室,四川成都610059

出　　处：《石油与天然气地质》2016年第4期473-482,共10页Oil & Gas Geology

基　　金：中国地质调查局项目(212011220758);财政部中央财政支持地方高校发展专项资金项目(11000-13Z00701)

摘　　要：通过对四川盆地东南部(简称川东南)寒武系娄山关群两剖面(京竹和中坝剖面)的白云岩样品进行岩石学和稀土元素特征研究,主要有微晶白云岩、颗粒白云岩、晶粒白云岩和鞍形白云石4种类型。稀土元素特征分析结果表明:14种类型的白云岩(石)均具有较低的稀土元素含量(平均含量为15.69×10-6)和较高的Y/Ho比值(平均值为50),且与铁锰含量相关性很弱,反映了研究区白云岩受陆源碎屑物和铁锰氧化物的污染较小。2不同类型白云岩(石)其稀土元素总含量有一定差别,泥微晶白云岩具有高的稀土元素含量(平均值为21.06×10-6),主要与其含有丰富的藻类有关;颗粒白云岩(平均值13.66×10-6)与晶粒白云岩(平均值13.02×10-6)具有相近的稀土元素含量;鞍形白云石具有较高的稀土元素含量(平均值为16.28×10-6),可能与热液参与有关。34种类型白云岩(石)均具有与灰岩相似的稀土配分模式,(Nd/Yb)SN平均值为1.52,相对轻稀土富集和重稀土亏损,负δEu和负δCe异常(平均值分别为0.79和0.36),显著Y正异常和La正异常,这些特征表明其白云岩化流体主要为海源性流体,成岩系统较封闭,成岩环境为还原环境,成岩温度较低。Petrologic study and REE （ rare earth element） characterization of dolomite samples from Jingzhu and Zhongba outcrops of the Cambrian Loushanguan Group in SE Sichuan Basin identified four types of dolomite： micritic dolomite, grain dolomite,crystalline dolomite and baroque dolomite. The analysis results of the REE characteristics show that all the 4 types have low REE content （avg. 15. 69ppm） and relatively high Y/Ho ratios （avg. 50）. The very poor correlation of REE content with Fe and Mn contents suggests a limited effect of terrigenous clastics and iron and manganese oxyhydrox-ide on the dolomite in the study area. Different types of dolomite vary in their total REE content readings. The micritic dolomite is rich in algae and has the highest content of REE （avg. 21. 06ppm）. The grain dolomite （avg. 13. 66ppm） and crystalline dolomite （avg. 13. 02ppm） have similar REE content. The baroque dolomite has relatively high REE con-tent （avg. 16. 28ppm）,indicating possible involvement of hydrothermal fluids. It also shows that all types of dolomite shares similar REE patterns with limestone. The average value of （Nd/Yb）SN in dolomite samples is 1. 52,indicating they are relatively rich in LREE and depleted in HREE. All the samples show negative Eu and Ce anomalies （avg. 0. 79 and 0. 36,respectively）. Significant positive Y anomalies and positive La anomalies were also observed. All these facts indi-cate that the dolomite was formed by fluids of marine origin in a relatively closed diagenetic system of relatively reducing environment and low temperature.

关 键 词：稀土元素 成岩流体 白云岩 娄山关群 寒武系 川东南地区 

分 类 号：TE121.3[石油与天然气工程—油气勘探]