塔里木盆地西北缘早寒武世玉尔吐斯组硅质岩成因  

Genesis of Early Cambrian cherts of the Yurtus Formation in northwestern Tarim Basin

作　　者：曹旭阳 韩以贵 鞠鹏程 鲁立辉 邵东 石震 CAO Xuyang;HAN Yigui;JU Pengcheng;LU Lihui;SHAO Dong;SHI Zhen(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,China;Key Laboratory of Crust-Mantle Materials and Environments,Chinese Academy of Sciences/School of Earth and Space Sciences,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]西北大学地质学系/大陆动力学国家重点实验室,陕西西安710069 [2]中国科学技术大学地球和空间科学学院/中国科学院壳幔物质与环境重点实验室,安徽合肥230026

出　　处：《西北大学学报（自然科学版）》2024年第4期715-728,共14页Journal of Northwest University（Natural Science Edition）

基　　金：国家自然科学基金(42072264);陕西省自然科学基础研究计划项目(2023JC-XJ-05)。

摘　　要：对塔里木盆地西北缘下寒武统玉尔吐斯组硅质岩开展岩石学以及元素与硅同位素地球化学研究,探讨硅质岩的成因及沉积模式。岩石学观察表明,玉尔吐斯组中段硅质岩主要由隐晶硅质和微晶石英组成,未见碎屑石英,排除了陆源输入对硅质岩沉积的影响。玉尔吐斯组下段硅质岩相对富Fe且具有显著的Eu正异常,反映了硅质岩可能主要来源于海底热液;而中段硅质岩显示Y/Ho比值较高、中等Ce负异常、LREE亏损和Y正异常,说明硅质来源主要为海水,这也符合中段硅质岩具有总体偏向热水来源的δ^(30)Si值。此外,氧化还原敏感元素指标表明,玉尔吐斯组硅质岩的沉积环境为表层海水氧化,而底层海水缺氧甚至硫化。研究认为,玉尔吐斯组硅质岩的沉积模式为:下段硅质岩由大量富硅热液在上升流作用下直接沉积,之后热液活动减弱,氧化还原分层海洋促进海水中溶解的硅和铁循环耦合,硅质以Fe^(3+)-Si胶体形式共沉积,当硫化水域盛行时铁和硅循环解耦,沉积黑色页岩,形成中段硅质岩和黑色页岩互层。This study employed petrological,elemental and silicon isotopic geochemical studies of the cherts from the lowest Cambrian Yurtus Formation in the northwestern margin of the Tarim Basin.The genesis and sedimentary model of the cherts were discussed.Petrological observations indicate that the cherts in the middle Yurtus Formation are mostly composed of cryptocrystalline and microcrystalline quartz without clastic quartz,which excludes the influence of terrigenous input on the chert deposition.The cherts in the lower Yurtus Formation are relatively Fe-rich and have a significantly positive Eu anomaly,which suggests that the cherts were likely originated from submarine hydrothermal fluids.In contrast,the middle Yurtus Formation cherts show high Y/Ho ratio,moderate negative Ce anomaly,LREE depletion,and positive Y anomaly,indicating that the cherts were mainly sourced from seawater.This is also consistent with their δ^(30)Si values that bias to hot water sources.In addition,the redox-sensitive element proxies indicate that the sedimentary environment of the cherts of the Yurtus Formation was probably oxidized for the surface seawater,while is anoxic or even euxinic for the bottom seawater.This study proposes that a sedimentary model for the cherts of the Yurtus Formation as follows:the cherts in the lower section were directly sourced from large amounts of silica-rich hydrothermal fluids under the influence of upwelling.Subsequently,the hydrothermal activities weakened and the redox-stratified ocean facilitated the coupled cycling of dissolved silicon and iron in seawater,and the silicon was co-deposited in the form of Fe^(3+)-Si colloidal.During the dominance of the euxinic zone,the iron and silicon cycle was decoupled,leading to the deposition of black shale and the formation of interbedded cherts and black shales in the middle section.

关 键 词：塔里木盆地 早寒武世 玉尔吐斯组 硅质岩 沉积环境 

分 类 号：P593[天文地球—地球化学]