应用方解石激光原位U-Pb同位素定年确定多旋回叠合盆地油气成藏绝对时间——以塔里木盆地塔河油田为例

Application of laser in-situ U-Pb dating of calcite to determination of the absolute time of hydrocarbon accumulation in polycyclic superimposed basins: A case study on Tahe oilfield, Tarim Basin

陈家旭 王斌 郭小文 曹自成 刘永立 耿锋 张旭友 徐豪 赵建新

Jiaxu Chen Bin Wang Xiaowen Guo Zicheng Cao Yongli Liu Feng Geng Xuyou Zhang Hao Xu Jianxin Zhao

多旋回叠合盆地油气成藏绝对时间一直是油气成藏研究需要解决的一个重大难题。以塔里木盆地塔河油田为例，在油包裹体观察和荧光光谱分析的基础上，通过阴极发光和微量元素分析划分方解石脉体形成期次，对不同期次方解石脉体进行激光原位U-Pb同位素定年获得油气充注绝对时间。研究结果表明，塔里木盆地塔河油田奥陶系储层方解石脉体中发育黄色和蓝白色荧光两种类型油包裹体。阴极发光和微区微量元素的差异性指示存在两期方解石脉体，其中发育黄色荧光原生油包裹体，两期方解石的年龄分别对应两期黄色荧光原油的充注时间。方解石脉体激光原位U-Pb同位素定年结果显示，第一期黄色荧光原油的充注时间为329.7 Ma±1.6 Ma，第二期充注时间为249.3 Ma±2.6 Ma~220.5 Ma±7.3 Ma。激光原位U-Pb同位素定年技术结合烃类流体包裹体分析可以很好地用于确定多旋回叠合盆地油气成藏时间，对重建油气成藏动态过程具有重要作用。

The absolute time of hydrocarbon accumulation in polycyclic superimposed basins has always been a major problem to be solved in the research of hydrocarbon accumulation. Based on the observation of oil inclusions and fluorescence spectrum analysis, we classify the generation of calcite crystallization into four stages by cathodoluminescence and trace elements analysis carried out in the Tahe oilfield, Tarim Basin; then determine the absolute time of hydrocarbon accumulation by laser in-situ U-Pb dating of calcite generated in these stages. The results show that two types of oil inclusions with yellow and blue-white fluorescent respectively are developed in calcite veins of the Ordovician in the study area. The differences of cathodoluminescence and micro-area trace elements indicate two stages of calcite veins contain primary oil inclusions with yellow fluorescent, the ages of which just correspond to the two charging episodes of yellow fluorescent crude oil. The laser in-situ U-Pb isotope dating results of calcite veins show that the first episode of yellow fluorescent crude oil charging occurred during 329.7 Ma±1.6 Ma, the second ran from 249.3 Ma±2.6 Ma to 220.5 Ma±7.3 Ma. An integration of the isotope dating technique and hydrocarbon fluid inclusion analysis can effectively determine the absolute time of hydrocarbon accumulation in polycyclic superimposed basins, and is of great significance to reconstructing the dynamic process of hydrocarbon accumulation.

10.11743/ogg20210611