东营凹陷岩盐原生流体包裹体中子矿物类型的拉曼光谱分析及其地质意义探讨

摘要

准确鉴定赋存于流体包裹体中的子矿物对于揭示沉积、成岩和成矿等地质过程中相关流体的地球化学信息具有重要的意义。而应用显微激光拉曼光谱技术分析子矿物的类型具有原位无损、灵敏度高、稳定性好以及简便快捷等优势,目前已得到了广泛地应用。利用显微激光拉曼光谱技术,首次对东营凹陷始新统沙四下亚段岩盐原生流体包裹体中子矿物的类型进行了准确地鉴定,并在此基础上,详细地探讨了子矿物对东营凹陷始新世盐湖古卤水地球化学特征的指示意义。研究结果显示：东营凹陷沙四下亚段岩盐原生流体包裹体中普遍发育有硬石膏(CaSO4)和四水泻盐(MgSO4·4H2O)两类子矿物。其中,硬石膏子晶以1018 cm-1的拉曼特征峰强度最大,同时还存在其它5个附属拉曼特征峰,依次为500,611,629,676和1131 cm-1；而四水泻盐子晶以1000 cm-1的拉曼特征峰强度最大,并且还存在其他三个附属拉曼特征峰,分别为462,618和1156 cm-1。这两类子矿物的存在表明岩盐的原始析盐母液中含有少量的 CaSO4和 MgSO4成分,且此时正值盐湖古卤水的早期蒸发析盐阶段,即：硫酸盐析出阶段的结束与氯化物盐析出早期阶段的开始,以析出石盐为主。此外,结合硬石膏和四水泻盐的沉淀温度,明确了东营凹陷始新世盐湖在早期蒸发析盐阶段时期,古卤水的温度介于37~61℃之间,表现为干旱的沉积环境。%Accurate identification of daughter minerals existed in fluid inclusions has a great significance for obtaining the geo-chemical information on fluids related to processes of sedimentation,diagenesis or mineralization,and using micro-Raman spectra to identify the types of daughter minerals is in-situ,nondestructive,high sensitive,good-stability,quick and convenient,so which has been widely used at present.In this paper,we used micro-Raman spectra,for the first time,to identify the types of daughter minerals in primary inclusions,which trapped in rock salt from the lower submember of Eocene Sha-4 member of Sha-hejie Formation (Es4x)in Dongying sag.On this basis,the indication significances of these daughter minerals to geochemical characteristics of paleo-brines in Eocene salt lake of Dongying sag were discussed in detail.The results show that anhydrite and starkeyite are the main daughter minerals in primary inclusions in rock salt of Es4x .Among them,anhydrite has strongest Raman band at 1 018 cm-1 and other five additional weaker bands at 500,611,629,676,1 131 cm-1 ,respectively.Starkeyite has strongest Raman band at 1 000 cm-1 and other three additional weaker bands at 462,618,1 156 cm-1 .These two kinds of daughter minerals existed in primary inclusions indicate that salt lake brines contained small amount of compositions of CaSO4 and MgSO4 ,the brines j ust reached early stage of evapo-concentrated precipitations at this moment,that is,the end of sulfates deposit and the beginning of early stage of rock salt deposit,and halite was the main product of brines precipitation.Moreover, based on the precipitation temperature of anhydrite and starkeyite,the temperature of paleo-brines of Eocene salt lake during the early stage of evapo-concentrated precipitations was determined,namely,the values of temperature ranged from 3 7 to 6 1 ℃ and sedimentary environment was featured by drought.