华北陆块2.56~2.52 Ga增氧事件对成矿和生命演化的影响
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本文为中国地质调查局中国矿产地质与成矿规律综合集成和服务项目(矿产地质志)(编号 DD20160346)资助的成果。


Effect of 2. 56~2. 52 Ga oxidation event on mineralization and life evolution in the North China block
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    摘要:

    地球表层大气氧浓度的显著增高是地球史上最重大的地质事件之一,它不仅改变了地球表层环境,促进了生命演化,而且加速了表生地质过程,形成一系列适应环境突变的岩石和重要矿床。地球在前寒武纪时期曾发生过两次大气快速增氧事件,分别为大氧化事件(GOE)和新元古代氧化事件(NOE)。本文主要论述华北陆块新太古代晚期增氧事件的时限及其对成矿和生命演化的影响。华北陆块新太古代晚期形成千余个氧化物相BIF型铁矿床和矿点,属于阿尔戈马型,累计查明资源储量约335. 36亿t,占全国铁矿总资源储量46%。该类矿床和矿点形成于弱碱性氧化环境,成矿时代主要介于2. 56~2. 52 Ga,并经历了2. 51~2. 50 Ga的变质作用。通过对BIF型铁矿床中矿石的Ce异常、铁同位素组成和硫同位素非质量分馏效应(MIFS)等特征研究,显示在2. 56~2. 52 Ga期间大气圈的氧浓度大幅度升高,并由缺氧还原环境变为具一定氧浓度(1%~10% PAL)的氧化环境,暗示华北陆块在此期间曾出现过一次显著的增氧事件。其对华北陆块的成矿作用产生了重要影响,主要表现在以下三个方面:① 形成大量氧化物相BIF型铁矿床,这是中国最重要的铁矿床类型和铁矿石开采对象,但缺少碳酸盐相BIF型铁矿床的产出;② 制约了新太古代晚期VMS型铜锌块状硫化物矿床的发育,目前仅在辽北红透山地区有报道;③ 缺失南非兰德型金铀砾岩矿床。此外,此次增氧事件也加速了华北陆块上生命演化的进程。一般来说,从以单细胞为主的真核生物演化到宏观多细胞真核生物大约需经历1. 6~1. 7 Ga。然而,华北陆块从新太古代晚期(2. 56~2. 52 Ga)的增氧事件到中元古代蓟县纪高于庄组宏观化石的发现,即从以单细胞为主的真核生物向宏观多细胞真核生物演化仅经历了约1. 0 Ga。上述研究结果表明,华北陆块上第一次出现显著增氧过程的时限为2. 56~2. 52 Ga,不仅时间上比全球其他地区(~2. 4 Ga)早了约1亿多年,而且生命演化也比其他地区提早0. 6~0. 7 Ga。

    Abstract:

    The significant increase in atmospheric oxygen concentration on the earth’s surface is one of the most important geological events in the earth’s history. It not only changed the earth’s surface environment and promoted the evolution of life, but also accelerated the supergene geological process, forming a series of rocks and important ore deposits adapted to the abrupt change of environment. During the Precambrian, the earth experienced two rapid atmospheric oxygen enrichment events, namely the Great Oxidation Event (GOE) and the Neoproterozoic Oxidation Event (NOE). This paper mainly discusses the time limit of the late Neoarcheanoxidation eventin the North China block and its influence on mineralization and biological evolution. In the late Neoarchean period, more than thousand oxide phase BIF type iron deposits and occurrences belonging to the Algoma type were formed in the North China block. The total identified reserves are about 33. 536 billion tons, accounting for 46% of the total iron ore reserves in China. These deposits and mineralised pit occurrences were formed in a weakly alkaline oxidation environment, and their metallogenic ages are mainly between 2. 56 Ga and 2. 52 Ga, and underwent metamorphism at 2. 51~2. 50 Ga. The characteristics of Ce anomaly, iron isotopic composition and MassIndependent Fractionation effect of sulfur isotope (MIF- S) in BIF type iron ore deposits show that the oxygen concentration in the atmosphere increased greatly during 2. 56~2. 52 Ga, and changed from anoxic reduction environment to oxidation environment with oxygen concentration (1%~10% PAL), implying that a significant oxygenation event occurred in the North China block during this period. The oxidation event has an important impact on the mineralization of the North China landmass, mainly in the following three aspects: (1) the formation of a large number of oxide phase BIF type iron ore deposits, which are the most important iron deposit typesmined in China, but lack carbonate BIF type iron ore deposits; (2) restricting the development of VMS type Cu, Zn massive sulfide deposits in the late Neoarchean, which is only reported in the Hongtoushan area, Northern Liaoning Province; (3) there is no Rand type gold uranium conglomerate deposit as in South Africa. In addition, the oxidation event accelerated the evolution of life on the North China block. Generally, it takes about 1. 6~1. 7 billion years to evolve from single cell eukaryotes to macro multicellular eukaryotes. However, from the late Neoarchean (2. 56~2. 52 Ga) oxidation event to the discovery of macro fossils from the Gaoyuzhuang Formation of Jixian period in the North China block, the evolution from single cell eukaryotes to macro multicellular eukaryotes only took about 1 billion years. The results show that the time limit of the first oxidation event is 2. 56~2. 52 Ga in the North China block, which is not only about 100 million years earlier than the other regions of the world (~2. 4 Ga), but also the life evolution is 600~700 million years earlier than other regions.

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沈保丰,毕君辉,张阔.2021.华北陆块2.56~2.52 Ga增氧事件对成矿和生命演化的影响[J].地质学报,95(2):336-351.
SHEN Baofeng, BI Junhui, ZHANG Kuo.2021. Effect of 2. 56~2. 52 Ga oxidation event on mineralization and life evolution in the North China block[J]. Acta Geologica Sinica,95(2):336-351.

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  • 收稿日期:2020-10-09
  • 最后修改日期:2020-11-12
  • 录用日期:2020-11-12
  • 在线发布日期: 2020-11-29