基于U-Pb同位素年龄和团簇同位素(Δ_(47))温度约束的四川盆地震旦系灯影组构造-埋藏史重建

Reconstruction of tectonic-burial evolution history of Sinian Dengying Formation in Sichuan Basin based on the constraints of in-situ laser ablation U-Pb date and clumped isotopic thermometer(Δ_(47))

目的层系构造—埋藏史曲线对成烃、成储和成藏史的研究有着非常重要的作用。前人基于区域地质背景、地层剥蚀厚度、构造运动幕次等地质认识恢复的构造—埋藏史,因构造运动幕次认识的不同,地层剥蚀厚度难以恢复,存在不确定性,尤其是经历多旋回构造运动改造的中国海相碳酸盐岩构造—埋藏史的重建。通过四川盆地震旦系灯影组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(Δ_(47))测温两项技术的应用,取得两项成果认识:(1)建立了四川盆地震旦系灯影组基于同位素年龄和Δ_(47)温度约束的构造—埋藏史曲线,解决了前人基于区域地质背景、地层剥蚀厚度和构造运动幕次等地质认识约束的构造—埋藏史曲线不确定性的问题;(2)基于同位素年龄和Δ_(47)温度约束的构造—埋藏史曲线,重新认识了灯影组气藏的成烃、成储和成藏史,指出该气藏经历了志留纪石油聚集、二叠纪石油聚集、燕山—喜马拉雅期天然气持续聚集和调整3个阶段。该案例揭示基于同位素年龄和Δ_(47)温度约束的构造—埋藏史恢复方法不但适用于经历多旋回构造改造的深层碳酸盐岩构造—埋藏史重建,而且在成烃、成储和成藏研究中具重要的应用价值。

Reliable evolution curve of tectonic-burial history is essential for the research of the source rock evolution,reservoir formation and hydrocarbon accumulation of target strata of basin.Previous publications reported the tectonicburial evolution history curves established depending on regional geological setting,formation(denuded)thickness,and tectonic movements,which were uncertain due to the difference in such geological understandings.For the ancient marine carbonates in China,which have experienced multiple tectonic movement reformation,it is more difficult to reconstruct tectonic-burial evolution history.In this paper,based on the identification of carbonate cements and the establishment of diagenetic sequence,through coupling carbonate laser ablation U-Pb dating and clumped isotope(Δ_(47))thermometer,two understandings were proposed:(1)The tectonic-burial curves of the Sinian Dengying Formation in the Sichuan Basin were established under the constraints of absolute age and temperature,which avoided the problems of uncertainty of tectonic-burial history curves in previous studies;(2)The new tectonic-burial history curve provided critical reference for study on the source rock evolution,reservoir origin and hydrocarbon accumulation of the Sinian Dengying Formation of the Sichuan Basin,revealing three stages of hydrocarbon accumulation in the Dengying gas reservoir including Silurian,Permian and Yanshanian-Himalayan periods.The proposed method of reconstructing tectonic-burial evolution curve is not only suitable for the ancient marine carbonates which experienced multiple tectonic movement reformation,but is also promising for the study of source rock evolution,reservoir origin and hydrocarbon accumulation.