华北克拉通南缘中元古代早期杂色页岩的古环境指示意义  

The study of Early Mesoproterozoic variegated shales in the southern North China Craton and its paleoenvironmental implications

作　　者：左鹏飞 祝禧艳[3] 郑德顺[1] 孙风波[1] 王世炎[4] ZUO PengFei;ZHU XiYan;ZHENG DeShun;SUN FengBo;WANG ShiYan(School of Resources and Environment,Henan Polytechnic University,Jiaozuo 454000,China;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;Henan Institute of Geology Survey,Zhengzhou 450001,China)

机构地区：[1]河南理工大学资源环境学院,焦作454000 [2]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [3]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 [4]河南省地质调查院,郑州450001

出　　处：《岩石学报》2022年第6期1713-1726,共14页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2020YFA0714803);地质过程与矿产资源国家重点实验室开放课题(GPMR202119);国家自然科学基金项目(42172131);河南省高校基本科研业务费专项资金(NSFRF210323)联合资助.

摘　　要：中元古代大气氧含量是否有变化以及何时、如何变化的,目前是尚不清楚、存有争议的热点问题。细碎屑岩常被认为可反映其沉积时的水体环境,是记录古海洋氧化还原信息的重要载体。华北克拉通自18亿年之后,处于多期裂解的陆内伸展环境,发育一系列泥页岩,其中华北克拉通南缘崔庄组(~1648Ma)泥页岩沉积于陆棚-浅海环境。本次研究选取该组杂色页岩作为研究对象,扫描电镜和粉晶衍射结果显示,绿色和紫红色页岩主要矿物包括伊利石、石英、长石,还包含了云母、绿泥石、赤铁矿。赤铁矿分布在云母内部和绿泥石边缘,指示其来自于矿物蚀变。两种页岩中的伊利石均以纤维状分布在长石、石英和云母碎屑粒间孔隙,且主要为1M型,指示其经历了浅成岩作用。紫红色页岩与绿色页岩相比,剖面上风化程度较高。主量元素显示,两种页岩的源岩都经历明显的钾化作用,经过钾校正之后,风化指数(CIA)约为80~85,说明物源区经历强烈的风化作用。同时,全铁含量与澳大利亚后太古代页岩和北美页岩相似,铁并无明显富集,指示铁可能是陆源输入。稀土元素与澳大利亚后太古代相比明显Eu异常,无明显Ce异常,而过渡金属元素(V、Cr、Co、Ni)无显著富集,其比值显示该套页岩沉积于氧化的水体中。结合该时期海洋分层模型,推测中元古代早期浅海陆棚海水已出现氧化。黏土质泥页岩在该时期广泛发育,均指示陆壳风化作用强烈,该过程可能影响和控制氧气含量的变化。The evolution of oxygen-increasing is one of the most significant events in the history of the Earth.It is controversial if there are variable oxygen levels in Proterozoic.Fine-grained sedimentary rocks,which record the redox state of the ocean sensitively,can be used in constraining the oxygen levels.A series of shales in the North China Craton(NCC)were deposited in extension environments after 1800Ma.Variegated shales,from the black shales in a shelf-neritic environment(ca.1648Ma),were carried out in mineralogy and geochemistry study.Scanning electron microscope and X-ray diffraction(XRD)show purplish-red and dark-green flaky shales mainly consist of illite,quartz and K-feldspar.Hematite distributes in biotite and chlorite and indicates its alteration genesis.Illite occurs as fibrous within intergranular pore among detrital K-feldspar,quartz and muscovite.Illite consists of 1M polytype suggesting very low-to low-grade metamorphism.The Chemical Index of Alteration(CIA)indicates intense weathering during the deposition of the shales.Compared with Post-Archean Australian Shales(PAAS),there is a slight enrichment in HREE,depletion in LREE and positive Eu anomalies.It is noted that enrichment of total iron has not been observed in the shales more than that of the PAAS and North America Shales(NASC)and,by extension,implying no anoxia.Transition trace elements(V,Cr,Co and Ni)show oxidized water column.It is reasonable to infer that neritic-shelf seawater has been oxidized in combination with a stratified model of the Mesoproterozoic Ocean.Meanwhile,contemporaneous clay and shale deposits also indicate intense weathering worldwide and it could be related to variable oxygen contents.

关 键 词：黑色岩系 华北克拉通 中元古代 氧化事件 

分 类 号：P575[天文地球—矿物学] P588.22[天文地球—地质学]