中元古代增氧事件:来自华北克拉通燕辽地区铁岭组的地球化学证据  

Geochemical evidence of shales in the Tieling Formation,North China Craton:Implications for Mesoproterozoic episodic oxygenation events

作　　者：何雨婷 祝禧艳[4,5] 仇一凡 李杰 赵太平[1,2,5] HE YuTing;ZHU XiYan;QIU YiFan;LI Jie;ZHAO TaiPing(Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Institutions of Earth Sciences,Chinese Academy of Sciences,Beijing 100029,China;State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China)

机构地区：[1]中国科学院广州地球化学研究所,中国科学院矿物学与成矿学重点实验室,广州510640 [2]中国科学院深地科学卓越创新中心,广州510640 [3]中国科学院大学,北京100049 [4]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [5]中国科学院地球科学研究院,北京100029 [6]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广州510640

出　　处：《岩石学报》2022年第6期1741-1755,共15页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2020YFA0714803);国家自然科学基金项目(41630211、41872198)联合资助.

摘　　要：氧气是生命演化的重要因素。近期的一些研究表明,元古宙两次大氧化事件之间的平静期存在多次幕式增氧事件,尤其是14亿年前后大气和海水的氧气水平有着很大程度的提高。但是,目前对于14亿年之前的表生环境氧化还原状态的研究仍存在不足。本次研究通过分析华北克拉通燕辽盆地中元古代~14.4亿年铁岭组绿色页岩的钼同位素组成、氧化还原敏感元素和稀土元素特征,发现绿色页岩的Fe含量和Mn含量较高,并显示富集轻的钼同位素组成(-1.00±0.07‰~-0.49±0.06‰)特征。Fe-Mn-Mo三者相关性表明,轻的Mo同位素主要以吸附共沉淀的形式进入铁锰(氢)氧化物,造成富铁的沉积物富集轻Mo同位素,而海水中Mo同位素偏重,指示绿色页岩沉积于氧化的水体之中。同时,氧化还原敏感元素含量及比值也指示铁岭组绿色页岩沉积时水体为氧化环境。研究结果表明,~14.4亿年前后发生了一次显著的增氧事件,使得当时海水氧化面积扩大,为早期生命演化提供了物质基础。Oxygen is one of the most important factors in the evolution of life.Some recent studies have shown that there were episodic oxygenation events during the quiet period between the two great oxidation events in the Proterozoic era,and the oxygen levels of the atmosphere and ocean were greatly increased around 1.4 billion years ago.However,it is far to confirm the redox state of the epigenetic environment before 1.4 billion years.In this study,molybdenum isotopic composition and characteristics of redox-sensitive elements and rare earth elements of green shales of the~1.44Ga Tieling Formation of the Yanliao Basin in the North China Craton were analyzed.It was found that the Fe and Mn contents of the green shales were high with enriched light molybdenum isotopic compositions(-1.00±0.07‰to-0.49±0.06‰).The Fe-Mn-Mo triadic correlation indicates that the incorporation of Fe-Mn(hydr)oxide by the form of adsorption co-precipitation,resulting in an enrichment of light Mo in Fe-rich sediments isotope,while the Mo isotope is heavier than that in seawater.It indicates these green shales were deposited in oxidized water bodies.In addition,the contents and ratios of redox-sensitive elements also reveal an oxidizing environment for the green shales of Tieling Formation.These results show that an oxygenation event should occur at~1.44 billion years ago with the expansion of seawater oxidation during this period,and the episodic oxygenation event in Mesoproterozoic may have provided material basis for the evolution of early life.

关 键 词：中元古代 铁岭组 绿色页岩 钼同位素 增氧事件 

分 类 号：P588.22[天文地球—岩石学]