西沙群岛西科1井三亚组一段致密白云岩围岩矿物及稀土元素特征

西沙群岛西科1井致密白云岩具有低孔低渗特征，前人证实其是由填隙物与围岩2个相互独立的岩石矿物学端元组成，同时西沙群岛远离陆架，其内碳酸盐岩中的地球化学指标尤其稀土元素可以很好地指示古海洋和沉积环境。作者以致密白云岩围岩为研究对象，通过显微观察、SEM-EDS(场发射扫描电子显微镜-X射线能谱仪)、激光原位剥蚀技术分析其矿物及稀土元素特征。结果表明围岩中白云石以细晶白云石为主，包括自形、半自形及他形，孔隙细小，发育典型雾心亮边构造。稀土配分表现为LREE亏损、La正异常、Ce负异常、高Y/Ho值等典型海相碳酸盐岩稀土元素特征。此外Eu具有正异常，认为与来自海底的热液活动有关。

Mineral and rare earth elements characteristics of tight dolomite surrounding rock in the Member 1 of Sanya Formation in Well Xike 1,Xisha Islands,China

Tight dolomite in Well Xike 1,Xisha Islands,which featured with low porosity and permeability,which is proven to be composed of two mutually-independent rock mineralogical end-members,interstitial material and surrounding rock according to previous studies. Moreover,since the Xisha Islands are far away from the continental shelf,the geochemical indexes of carbonate rocks on the islands,especially the rare earth elements,are great indicators for the paleo-ocean and sedimentary environment. Hence,the surrounding rock of tight dolomite was studied over its minerals and rare earth elements by means of microscopic observation,SEM-EDS(Scanning Electron Microscope-Energy Dispersive Spectrometer)and laser in-situ denudation technology. The findings show that the surrounding rock is dominated by fine-grained dolomite in automorphic,hypautomorphic and xenomorphic properties with small pores,where developed typical structure with fogged center and clear margin. Further,typical rare earth elements of marine carbonate rocks such as LREE depletion,La positive anomaly,Ce negative anomaly,and high Y/^Ho value are represented in the rare earth element distribution is characterized by. In addition,Eu with positive anomaly is thought to be associated with the seabed hydrothermal activity.