地学前缘 ›› 2018, Vol. 25 ›› Issue (4): 99-115.DOI: 10.13745/j.esf.yx.2017-12-28

• 岩（矿）石、地层特征及地质意义 • 上一篇    下一篇

中国东部大陆尺度地球化学走廊带碳酸盐岩稀土元素分布特征与影响因素

柳青青，迟清华，王学求，周建，刘汉粮，刘东盛，高艳芳，翟大兴   

  1. 1. 国土资源部地球化学探测技术重点实验室; 中国地质科学院 地球物理地球化学勘查研究所, 河北 廊坊 065000
    2. 联合国教科文组织全球尺度地球化学国际研究中心, 河北 廊坊 065000
    3. 河北省地球物理勘查院, 河北 廊坊 065000
  • 收稿日期:2017-05-15 修回日期:2017-08-03 出版日期:2018-07-15 发布日期:2018-07-15
  • 作者简介:柳青青(1986—),女,硕士,工程师,从事应用地球化学研究。E-mail：liuqingqing@igge.cn
  • 基金资助:
    中国地质科学院基本科研业务费项目(AS2016P02)；国家公益性行业科研专项(SinoProbe-04-05)；国家重点研发计划项目“穿透性地球化学勘查技术”(2016YFC0600600)；中国地质调查局化学地球国际合作计划或全球地球化学填图计划(DD20160116)

Distribution and influencing factors of rare earth elements in carbonate rocks along three continentalscale transects in eastern China.

LIU Qingqing,CHI Qinghua,WANG Xueqiu,ZHOU Jian,LIU Hanliang,LIU Dongsheng,GAO Yanfang,ZHAI Daxing   

  1. 1. Key Laboratory of Geochemical Exploration,Ministry of Land and Resources; Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang 065000, China
    2. UNESCO International Centre on GlobalScale Geochemistry, Langfang 065000, China
    3. Hebei Institute of Geophysical Exploration, Langfang 065000, China
  • Received:2017-05-15 Revised:2017-08-03 Online:2018-07-15 Published:2018-07-15

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摘要： 碳酸盐岩是地球表层岩石圈的重要组成部分，其化学组成可提供沉积环境与海洋水体演化等信息，然而，前人对碳酸盐岩中稀土等元素的分布与变化特征关注不足。本文选择穿越中国东部6个一级大地构造单元的3条地球化学走廊带，系统采集了582件碳酸盐岩地层样品，并准确分析了包括稀土元素(REE)在内的81项指标的含量。结果表明，中国东部地球化学走廊带碳酸盐岩稀土元素(REE＋Y)总量为(0.59～183)×10-6，均值为24.0×10-6，纯净碳酸盐岩(CMC含量≥99％)均值为4.80×10-6。PAAS标准化后其显示具有轻稀土相对于中稀土和重稀土略亏损、δEu轻微正异常、δCe中度负异常等特征。白云岩中稀土含量、LREE/HREE值一般低于石灰岩；砂泥质含量相近时，前中生代各时代碳酸盐岩稀土分布模式相差不大，各构造单元稀土分布特征基本相似；与其他时代相比，中生代及中新元古代碳酸盐岩具有相对较平坦的稀土分布模式。研究表明，碳酸盐岩中稀土分布受碎屑物质影响明显，表现为稀土元素含量与碳酸根负相关，与碎屑物质相关元素(Si、Ti、Rb、Cs、Th、Zr等)、黏土相关元素(Al、Fe、K等)等正相关。成岩过程及白云化过程对较纯净碳酸盐岩中稀土分布特征影响不明显。我国古生代纯净碳酸盐岩分布模式受控于海相环境，其分布模式与现今海水相近；中生代纯净石灰岩受到陆相或海陆交互相的影响，具有较平坦的稀土分布模式。氧化还原条件对δCe的影响较δEu更为明显，δCe值受海相环境控制，极端正异常值(δCe＞1.3)受到还原环境或/和热液影响。若假定海水中REE自中元古代至今无太大变化，各时代稀土元素分配系数均值介于103.55～102.39，分配系数差异是造成碳酸盐岩中轻稀土亏损、Ce负异常及Y正异常的主要原因。微生物(席)可富集稀土等金属元素并改变沉积环境，这可能是造成中新元古界碳酸盐岩较平坦的稀土分布模式的主要原因。

关键词: 地球化学走廊带, 稀土元素, 碳酸盐岩, 沉积环境

Abstract: As an important part of the lithosphere on the earth surface, the carbonate rocks chemical composition can provide useful information on their sedimentary environment and evolution of marine waters. However, previous studies paid little attention to the distribution characteristics of rare earth elements and other elements in the carbonate rocks. This study examined a total of 582 carbonate rock samples collected along three continentalscale transects in eastern China. The results show that the total concentrations of REE＋Y in the carbonate rocks ranged from 0.59×10-6 to 183×10-6 (average 24.0×10-6), with the mean of 4.80×10-6 in the pure carbonate rocks (CMC≥99％). Compared with MREE and HREE, LREE depletion was observed after PAASnormalization, with weak positive δEu anomaly and moderate negative δCe anomaly. Values of REEs and LREE/HREE in dolomite were generally lower than those in limestone. When the contents of sand and mud were similar, the distribution patterns of carbonate rocks were similar in different tectonic units during the preMesozoic era. Compared with the other eras, the Mesozoic and Mesoproterozoic carbonate rocks had relatively flat distribution patterns. This study proves that the distribution of REEs in carbonate rocks is obviously influenced by detrital material. Meanwhile, the concentrations of REE＋Y were negatively correlated with CO2-3 and positively correlated with the elements in the detrital material (Si, Ti, Rb, Cs, Th, Zr, etc) and in clay (Al, Fe, K, etc). The diagenesis and dolomitization had little effect on the distribution of REE＋Y in the pure carbonate rocks. The distribution pattern of Paleozoic pure carbonate rocks in eastern China was controlled by the marine environment, which was very similar to the pattern of current seawater. The Mesozoic pure limestone was affected by terrestrial facies or marineterrigenous facies, with a relatively flat REE＋Y distribution pattern. The δCe value was controlled by the marine environment, and the extreme positive anomaly (δCe＞1.3) was affected by the reducing environment/hydrothermal solution, which led to even more significant effect of redox conditions on the δCe than δEu. When the REEs in seawater had no obvious change since the Middle Proterozoic, and the mean value of REE＋Y partition coefficient was between 103.55 and 102.39, the LREE depletion, negative anomaly of Ce and positive anomaly of Y were mainly due to differences in the distribution coefficient. Microorganisms could enrich REEs and change the sedimentary environment, it might be the main reason for the flat REE＋Y distribution pattern in the MiddleUpper Proterozoic carbonate rocks.

Key words:  continentalscale transects in eastern China, rare earth elements, carbonate rocks, sedimentary environment

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