地学前缘 ›› 2024, Vol. 31 ›› Issue (1): 111-126.DOI: 10.13745/j.esf.sf.2023.11.8

• 华北克拉通演化及其效应 • 上一篇    下一篇

条带状铁建造消失之谜:铁-硅互层机制研究进展与展望

王瑞敏(), 沈冰*()   

  1. 北京大学 地球与空间科学学院 造山带与地壳演化教育部重点实验室, 北京 100871
  • 收稿日期:2023-10-20 修回日期:2023-11-06 出版日期:2024-01-25 发布日期:2024-01-25
  • 通讯作者: *沈 冰(1979—),男,博士,教授,博士生导师,主要从事地球生物学、天体生物学、低温地球化学和古生物学的研究。E-mail: bingshen@pku.edu.cn
  • 作者简介:王瑞敏(1998—),女,博士研究生,主要从事早期地球环境演化、地球生物学和低温地球化学研究。E-mail: ruiminwang@pku.edu.cn
  • 基金资助:
    科学技术部重点研发计划项目(2021YFA0718200);国家自然科学基金项目(42225304)

The disappearance of banded iron formations: Research progress and perspectives on the origin of rhythmic Fe-rich/Si-rich laminae

WANG Ruimin(), SHEN Bing*()   

  1. MOE Key Laboratory of Orogenic Belt and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing 100871, China
  • Received:2023-10-20 Revised:2023-11-06 Online:2024-01-25 Published:2024-01-25

摘要:

条带状铁建造(banded iron formation,BIF)是指以铁-硅韵律层结构为特征的化学沉积岩。BIF不仅是重要的铁资源,也是记录早期地球演化、早期微生物活动和大气-海洋氧化还原状态的重要载体。BIF的出现和消失与重要环境事件的演变密切相关。BIF在>3.8 Ga首次出现,并在第一次大氧化事件前大量形成,在1.8~0.8 Ga沉积中断,而在成冰纪雪球地球冰期中复现,最终消失在显生宙的氧化海洋中。传统模型认为BIF的出现与消失主要受控于海洋中Fe(II)离子的含量。在1.8~0.8 Ga期间,构造-岩浆-热液活动减弱,海洋氧化还原剧变(氧化/硫化)导致海水中的Fe(II)被大量耗尽,BIF消失。然而,地球化学证据表明中元古代深海区域仍处于铁化状态,即Fe(II) 可以稳定存在的氧化还原状态;沉积学证据也表明中元古代仍有大量的铁岩沉积。这些富铁沉积的大量出现,表明中元古代的海洋仍具有沉积铁岩/富铁层的条件,只是不再出现BIF这种“铁-硅互层”的韵律沉积。因此,BIF在1.8~0.8 Ga的沉积中断并不是由Fe(II)耗尽造成的,而很可能与海水中铁-硅循环变化导致“铁-硅互层”沉积模式的改变有关。本文对BIF的地质学特征进行了概述,深入探讨了BIF中富铁-富硅层的沉积模式,并从Fe(II)的来源差异和Fe(II)的氧化差异及Fe(III)的保存差异3方面全面综述了BIF “铁-硅互层”机制的研究进展。在此基础上,尝试找出解决中元古代BIF消失之谜的可能方向。最后,对BIF的成因机制所承载的前寒武纪铁-硅生物地球化学循环、早期地球演化过程和早期生命信息等方面提出展望。

关键词: 条带状铁建造, 铁循环, 硅循环, 韵律层沉积, 前寒武纪

Abstract:

Banded iron formations (BIFs) are chemical sediments consisting of rhythmic Fe-rich and Si-rich laminae that are millimeters to centimeters thick. BIFs not only are an important iron resource, but also record the Earth's early evolution, early microbial activity, and atmosphere-ocean redox status. First appeared prior to 3.8 Ga, BIFs were common in the Archean and Paleoproterozoic, but they started to disappear about 1.8-0.8 Ga and were absent throughout the rest of Earth's history except for a brief appearance in the Cyogenian during global glaciation. The traditional model suggests that the abundance of BIFs is mainly controlled by dissolved Fe(II) contents in the ocean, and weakened tectonic/magmatic/hydrothermal activities, ocean oxidation, or oceanic euxinia about 1.8-0.8 Ga were responsible for the depletion of Fe (II) in the mid-Proterozoic ocean to drive to BIFs to disappear. However, geochemical evidence revealed that mid-Proterozoic ocean was predominantly ferruginous (Fe2+ rich) with large amounts of non-BIF ironstone deposits, challenging the traditional model. Here, we argue that the disappearance of BIFs in the mid-Proterozoic might result from changes in rhythmic deposition of Fe-rich/Si-rich laminae. We review the geological characteristics of BIFs and discuss different deposition models in detail. Additionally, we comprehensively review recent researches on the origin of rhythmic Fe-rich/Si-rich laminae in BIFs focused on Fe (II) source, Fe(II) oxidation, and Fe(III) preservation in sediments. Based on this, we attempt to identify possible directions for solving the mystery of BIFs’ disappearance by considering the coupling between iron and silicon biogeochemical cycles, so as to develop new insights into the evolution of the early Earth.

Key words: banded iron formation, Fe cycle, Si cycle, rhythmic laminae, Precambrian

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