西藏隆鄂尼—昂达尔错地区布曲组白云岩地球化学特征及成因

Geochemical Characteristics and Genesis of Buqu Dolomite in Longeni-Angdaercuo Area,Tibet

西藏隆鄂尼—昂达尔错地区中侏罗统布曲组白云岩，是一个具有含油远景的层系，查明其成因，对于正确评价研究区含油远景具有重要意义。为此，对研究区含油白云岩的流体包裹体和碳、氧同位素进行了分析。研究区白云石环带内流体包裹体的均一温度和盐度较高，均一温度集中在130~170℃，盐度集中于3.5%~4.5%，显示白云石环带形成环境的温度及盐度较高，应为深埋藏到成岩晚期产物。白云岩δ18OPDB均小于零且变化范围较大，并向负值偏移，具有低温白云岩和高温白云岩成因。结合大量野外调查和室内测试分析，认为研究区白云岩成因复杂，至少为3期成因的复合，即早期低温准同生白云岩化，中期高温深埋藏白云岩化，晚期构造白云岩化。

The Buqu dolomite of the Middle Jurassic in Longeni-Angdaercuo area in Tibet is a sequence with petroliferous prospect. To understand its genesis is very significant for accurate evaluation of petroliferous potential in the study area. This paper analyzes the fluid inclusion, carbon and oxygen isotopes in oil-bearing dolomite in this area, showing that the homogenization temperature mainly ranges from 130℃ to 170℃ and the salinity mainly ranges from 3.5% to 4.5% of fluid inclusion in dolomite zones, which indicates that the dolomite zone-formed environment temperature and salinity are all relatively high and they should be the products of deep-burial to late-stage diagenesis. All the δ18OPDB values of dolomite are less than zero （migrating toward negative values） and vary largely, indicating the low-temperature and high-temperature genesis of dolomite. Based on the combination of field survey and indoor test and analysis, it is considered that the dolomite in the study area experienced a complex genesis—at least the compound of 3 stages of genesis, namely low-temperature penecontemporaneous dolomitization at the early stage, high-temperature and deep-burial dolomitization at the middle stage and structural dolomitization at the late stage .