| 胶-辽-吉造山带辽河群石墨矿碳同位素特征及成因分析 |
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| 引用本文： | 朱建江,刘福来,刘福兴,石闯,王舫,徐文涛.胶-辽-吉造山带辽河群石墨矿碳同位素特征及成因分析[J].岩石学报,2021,37(2):599-618. |
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| 作者姓名： | 朱建江 刘福来 刘福兴 石闯 王舫 徐文涛 |
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| 作者单位： | 自然资源部深地动力学重点实验室, 中国地质科学院地质研究所, 北京 100037;辽宁省有色地质一〇三队有限责任公司, 丹东 118008 |
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| 基金项目： | 本文受国家自然科学基金项目（92062214、41430210、41890833、42002060）、中国地质科学院基本科研业务费（J2009）和自然资源部深地动力学重点实验室自主研究课题（J1901-23）联合资助. |
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| 摘 要： | 作为华北克拉通周缘三条石墨成矿带之一的东部带,胶-辽-吉古元古代石墨成矿带是研究早前寒武纪石墨成矿机制及地球早期气候特征的天然实验室。本文对胶-辽-吉造山带辽河群石墨矿(甜水乡马沟石墨矿)进行了详细的岩相学、地球化学、拉曼光谱学以及碳同位素等方面的研究。研究结果表明辽河群含石墨矿岩石主要为含石墨变质杂砂岩、含石墨黑云母长英质片麻岩和含石墨透闪大理岩,在log(Fe2O3/K2O)-log(SiO2/Al2O3)判别图解中,这些含石墨岩石位于砂岩和页岩区域内,它们具有和太古宙后澳大利亚平均页岩(PAAS)相似的稀土元素特征;地球化学特征表明它们具有低的成熟度,未经历长途搬运,是快速堆积的产物,主要沉积于活动大陆边缘弧后盆地环境。碳同位素研究表明辽河群石墨矿碳同位素值具有很宽的变化范围(δ13CPDB=-16.49‰~-25.93‰),是有机物在变质过程中脱CH_4造成的。结合拉曼光谱学特征,我们认为辽河群石墨矿是由有机物经过变质作用形成的,其变质程度可以达到高角闪岩相(551~627℃)。综合分析前人年代学数据,我们认为辽河群石墨矿的沉积时代为2.13~2.17Ga,在后期的弧-陆碰撞造山以及后碰撞作用过程中(2000~1895Ma;1875~1850Ma),有机物逐渐发生变质形成石墨并聚集形成石墨矿床。华北克拉通周缘大量石墨矿的沉积时代(2.3~2.05Ga)和大氧化事件发生的时间一致,可能是地球早期大氧化事件的沉积响应。
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| 关 键 词： | 胶-辽-吉造山带 辽河群 石墨矿 碳同位素 大氧化事件 |
| 收稿时间： | 2020/6/29 0:00:00 |
| 修稿时间： | 2020/10/18 0:00:00 |
Carbon isotope and genesis studies of graphite deposits in the Liaohe Group of the Jiao-Liao-Ji Orogenic Belt |
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| ZHU JianJiang,LIU FuLai,LIU FuXing,SHI Chuang,WANG Fang,XU WenTao.Carbon isotope and genesis studies of graphite deposits in the Liaohe Group of the Jiao-Liao-Ji Orogenic Belt[J].Acta Petrologica Sinica,2021,37(2):599-618. |
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| Authors: | ZHU JianJiang LIU FuLai LIU FuXing SHI Chuang WANG Fang XU WenTao |
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| Institution: | Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Science, Beijing 100037, China;The Bureau of Non-ferrous Neology of Liaoning Province 103 Limited Liability Branch Company, Dandong 118008, China |
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| Abstract: | As the eastern part of the three graphite metallogenic belts around the North China Craton,the Jiao-Liao-Ji Proterozoic graphite metallogenic belt is a natural laboratory for studying the mechanism of Early Precambrian graphite mineralization and the characteristics of early Earth climate.In this study,we performed detailed petrological,geochemical,Raman spectroscopy,and carbon isotope studies for the graphite deposits in the Liaohe Group(Magou graphite deposits in Tianshui Country)of the Jiao-Liao-Ji Orogenic Belt.The results show that the graphite-bearing rocks in the Liaohe Group are mainly graphite-bearing meta-greywacke,graphitebearing biotite feldspar gneisses,and graphite-bearing tremolite marble.These graphite-bearing rocks are located in the sandstone and shale regions in the log(Fe2O3/K2O)-log(SiO2/Al2O3)diagram,and have similar rare earth elements characteristics with PostArchean Australian Average Shales(PAAS).Geochemical features show that they have low maturity,and are the products of rapid accumulation without a long-distance transportation,which indicate that they are mainly deposited in the back-arc basin of an active continental margin.The carbon isotope study shows that the carbon isotope values of the graphite deposits in the Liaohe Group have a wide range of variation(δ^13 CPDB=-16.49‰~25.93‰),which is caused by the demethanation of organic matter during metamorphism.Combined with the Raman spectrum of the graphite deposits,we propose that the graphite deposits in the Liaohe Group are formed by the metamorphism of organic matter,and its metamorphism can reach high amphibolite facies(551~627℃).Based on the comprehensive analysis of the previous geochronology data,we suggest that the protolith of the graphite deposits were deposited at2.13~2.17 Ga,the organic matter trapped within these sediments gradually metamorphosed into graphite and agglomerated into graphite deposits during the later arc-continent collision and post-collision stages(2000~1895 Ma;1875~1850 Ma).The sedimentary age(2.3~2.05 Ga)of a large number of graphite deposits around the North China Craton coincides with the time of the Great Oxidation Event(GOE),which may be the sedimentary response of the GOE in the early Earth. |
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| Keywords: | Jiao-Liao-Ji belt Liaohe Group Graphite deposits Carbon isotope Great oxidation event |
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