中上扬子区上二叠统大隆组硅质岩沉积终结年龄  

Termination Age of the Chert Deposits in the Late Permian Dalong Formation in Middle and Upper Yangtze Area,China

作　　者：韦恒叶 张淦 张璇 胡谍 龚嘉欣 WEI HengYe;ZHANG Gan;ZHANG Xuan;HU Die;GONG JiaXin(School of Geoscience and Technology,Southwest Petroleum University,Chengdu 610500,China;Qiangtang Institute of Sedimentary Basin,Southwest Petroleum University,Chengdu 610500,China;State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu 610500,China)

机构地区：[1]西南石油大学地球科学与技术学院,成都610500 [2]西南石油大学羌塘盆地研究院,成都610500 [3]西南石油大学油气藏地质与开发工程国家重点实验室,成都610500

出　　处：《沉积学报》2024年第6期2135-2143,共9页Acta Sedimentologica Sinica

基　　金：国家自然科学基金项目(42272118);四川省自然科学基金项目(2023NSFSC0279)。

摘　　要：【目的】晚二叠世扬子板块北缘台地内部盆地广旺海槽、开江—梁平海槽与鄂西海槽发育大隆组富有机质的黑色硅质岩沉积,是四川盆地二叠系页岩气勘探的目标层位。这套硅质岩开始沉积于258.77 Ma,其形成与峨眉山地幔柱活动有关,但硅质岩沉积结束的具体年龄以及这些海槽消亡的原因尚不清楚。开展相应的研究有助于深入了解扬子北缘这些深水海槽的演化与发展,为二叠系页岩气勘探潜力评价提供理论依据。【方法】采集位于广旺海槽的旺苍燕儿洞剖面上二叠统大隆组硅质岩上部火山灰夹层样品,开展锆石激光剥蚀电感耦合等离子体质谱仪(LA-ICP-MS)分析,测定锆石U-Pb年龄以及微量元素。【结果】锆石为自形棱角状,发育生长环带,Th/U≥0.46,球粒陨石标准化的稀土配分曲线展示重稀土富集、轻稀土亏损、Ce正异常、Eu负异常的左倾特征;锆石铀铅年龄为253.0±1.3 Ma;锆石微量元素Th/Nb与Hf/Th交会图以及Th/U与Nb/Hf交会图指示岛弧造山构造背景。【结论】华南大隆组硅质岩沉积终结于晚二叠世长兴中期253.0±1.3 Ma,该期火山喷发与板内造山的峨眉山地幔柱活动无关,其形成与扬子板块周围岛弧火山作用有关,后者可能与扬子北缘多个海槽在二叠纪末期萎缩消失密切相关。[Objective]Several intraplatform deep-marine trough basins in the northern Yangtze Platform developed bedded chert in the Dalong Formation during the Late Permian.The organic-rich black rocks in the trough basins are shale gas exploration targets in the Sichuan Basin.The black chert deposition in the Dalong Formation started at 258.77 Ma,related to waning of the Emeishan mantle plume.However,its termination date and the cause of the disappearance of the intraplatform trough basins were still unclear.The results of this study help to better understand the evolution of these deep-marine troughs,offering a theoretical basis for potential assessment and exploration of Permian shale gas.[Methods]Zircon U-Pb LA-ICP-MS age dating and trace element measurement in the bentonite interbeds were carried out in the upper part of the Dalong Formation chert beds[.Results]The zircon grains are euhedral and show clear zoning,with Th/U ratios higher than 0.46.The zircon grains are enriched in heavy rare earth elements(HREE)with positive Ce anomalies and negative Eu anomalies,showing a rising trend from light REE to HREE in the chondrite-normalized REE patterns.The U-Pb LA-ICP-MS age of the zircon was 253.0±1.3 Ma.Diagrams of Th/Nb vs.Hf/Th and Th/U vs.Nb/Hf in the zircon show arc magma origin[.Conclusions]Chert deposition in the Dalong Formation in South China ceased in the mid-Changhsingian Stage of the Late Permian at 253.0±1.3 Ma.The arc volcanism eruption was not related to intraplate Emeishan mantle plume activity,but was caused by arc activity around the Yangtze Block,and was probably related to the disappearance of the deep-marine troughs in the northern Yangtze area.

关 键 词：U-PB定年 岛弧火山 大隆组 晚二叠世 四川盆地 海槽消亡 

分 类 号：P595[天文地球—地球化学]