辽河西部凹陷雷家地区古近系沙四段湖相白云岩成因

通过岩石学特征、主微量元素、碳氧同位素等地球化学特征分析,明确了辽河西部凹陷雷家地区古近系沙四段湖相白云岩的成因.研究结果表明:①研究区白云岩沉积时,湖盆水体较咸,且处于强还原环境,以泥晶级白云岩为主,有均匀分散型、纹层状富集型2种产状.②研究区白云岩的δ18O值平均为-4.4‰,δ13C值平均为8.7‰,整体上具有"...

Genesis of lacustrine dolomites of the fourth member of Paleogene Shahejie Formation in Leijia area,Western Liao Depression

The petrological characteristics,major and trace elements,carbon and oxygen isotopes and other geochemical characteristics were used to analyz the genesis of lacustrine dolomites of the fourth member of Paleogene Shahejie Formation in Leijia area of Western Liaohe Depression.The results show that:(1)During the deposition of dolomites in the study area,the lake basin water bodies were relatively salty and in a strong reducing environment,dominated by micritic dolomites,with two types of occurrences:uniform dispersion and laminar enrichment.(2)The average values ofδ¹⁸O andδ¹³C of the dolomites in the study area are-4.4‰and 8.7‰respectively,the carbon isotope is positive and the oxygen isotope is negative,reflecting the characteristics of overall salinized water body.The cathodoluminescence test results are no luminescence or dim light,dark red and orange light.The rare earth elements are relatively enriched in light rare earth elements,and weak Eu positive anomaly.The distribution model of rare earth elements shows that the analcite-bearing dolomites have a certain affinity with the alkaline basalts of the underlying Fangshenpao Formation and the basalts in the same layer.(3)There are two genetic types of dolomites in the study area:quasi-syngenetic dolomitization and hydrothermal sedimentary dolomitization.The quasi syngenetic dolomitization is dominated by argillaceous structure,with fine grains,low order of dolomite and rich-calcium and poor-magnesium,which is metasomatized by high salinity lake water.Deep hydrothermal fluids carrying a large number of cations spewed out of the surface and mixed with lake water to form hydrothermal sedimentary rocks.