羌塘盆地隆额尼—昂达尔错古油藏的白云岩组构特征及铅同位素意义

The Dolomite Fabric Characteristics and Lead Isotope Significance of the Ancient Oil Accumulation in Long'eni-Angdar Lake,Qiangtang Basin

以系统的岩石学及沉积相分析为基础,深入探讨了隆额尼—昂达尔错古油藏白云岩及其伴生灰岩的铅同位素特征,认为该区白云岩及伴生灰岩具有统一的铅来源,铅主要来自中央隆起带变质岩、岩浆岩及再旋回沉积的三叠系地层,为地幔、造山带、地壳等多源混合的异常铅。铅元素在含量上与沉积相带关系十分明显,仍受沉积过程的控制,后期构造作用并未带入大量深部流体进行白云岩的交代作用。该区白云岩仍保存有大量具成因意义的组构信息,主要体现在:典型混合水交代成因的雾心亮边结构、等厚环边和世代生成结构、残余鲕粒结构及藻纹层构造等,该区白云岩为混合水交代成因。构造只是起到白云岩化后期的改造作用。

Based on a systematic lithologie and sedimentary facies analysis, this paper deals in detail with Pb isotope charac-teristics of dolomite and associated limestone in the Long＇ eni-Angdar Co ancient oil accumulation. The dolomite and associated calcite seem to have the same Pb source, which was derived mainly from metamorphic rocks, magmatic rocks and recycled Triassic deposits in the uplift area of Qiangtang basin, thus probably being multi-source mixed anomalous lead from the mantle, the orogenic belt and the crust. The Pb content has distinctive relationship with sedimentary facies, still under the control of the sedimentary process. Late tectonic activities did not bring large quantities of hot fluids from the interior of the earth for the replacement of dolomite, and hence dolomite Still preserves many typical structures of genetic significance, such as fogged center and clear margin, ring structure and generations of minerals, remnant oolitic texture and algal stroma-tolite. The dolomite might have resulted from mixed water replacement of calcite, and tectonic activities only exerted late alteration effects on dolomite.