基于U-Pb同位素年龄和团簇同位素(Δ_(47))温度约束的构造-埋藏史重建——以塔里木盆地阿克苏地区震旦系奇格布拉克组为例

Reconstruction of tectonic-burial evolution based on the constraints of laser in situ U-Pb date and clumped isotopic temperature:a case study from Sinian Qigebulak Formation in Akesu area, Tarim Basin

构造-埋藏史恢复是成烃、成储和成藏史研究的重要内容。通过塔里木盆地震旦系奇格布拉克组露头和镜下多期次碳酸盐胶结物的识别和成岩序列的建立,碳酸盐矿物U-Pb同位素测年和团簇同位素(Δ47)测温2项技术的应用,取得2项成果认识:(1)建立了塔里木盆地奇格布拉克组基于同位素年龄和Δ47温度约束的构造-埋藏史曲线,解决了前人基于地质认识的构造-埋藏史曲线不确定性的问题;(2)基于同位素年龄和Δ47温度约束的构造-埋藏史曲线,建立了储层成岩作用-成岩环境-地球化学特征和演化图谱及定时定量的成岩-孔隙演化史曲线,为理解区域构造地质背景控制下孔隙改造事件、成孔效应提供了基础,并指出储集空间主要形成于沉积和早表生环境,埋藏环境通过胶结作用逐渐减孔。

Reliable tectonic-burial evolution curve is essential for the research on the source rock evolution, reservoirs origin and hydrocarbon accumulating of target strata of the basin. Previous publications reported the tectonic-burial evolution curves depending on regional geological setting, formation(denuded) thickness, and tectonic movements, which are uncertain due to the difference in these geological understandings. For the ancient marine carbonates which went through multicycle tectonic reformation, it is more difficult to reconstruct tectonic-burial evolution history. In this paper, based on the identification of carbonate cements and establishment of diagenetic sequence, by coupling carbonate laser U-Pb dating and clumped isotope(Δ_(47))thermometer, two understandings were obtained:(1)the tectonic-burial curves of the Sinian Qigebulak Formation of the Tarim Basin are established under the constraints of absolute age and temperature, avoiding the problems of uncertainty of tectonic-burial history curves in previous studies;(2)the new tectonic-burial evolution curve provide critical reference for mapping the diagenesis-diagenetic environment-geochemical characteristics and evolution curve and the quantitative diagenesis-porosity evolution curve, allowing thequantitative analysis of pores formation and transformation, revealing that the pores in the Sinian Qigebulak Formation are mainly formed in the supergene environment and gradually decrease in the burial environment due to the cementation. The proposed method is worthy of popularization in the study of reservoir-forming and diagenetic geochronology for ancient marine carbonate strata.