国内外前寒武纪条带状铁建造研究现状

An Overview of Studies on Precambrian Banded Iron Formations(BIFs) in China and Abroad

条带状铁建造(BIFs)主要发育于早前寒武纪时期(3.8~1.8Ga),记录了早期地球演化的重要信息且蕴含丰富的铁矿石资源。本文梳理总结了国内外BIF相关领域的研究认识及存在问题:1统计对比显示,BIF沉积事件与地幔柱、地壳增生等重大地质事件相关;2稀土元素及Nd同位素示踪表明,Fe来源于海水与海底高温热液的混合溶液,其中高温热液与海水比例为1:1000;3 BIFs缺乏负Ce异常且富集重Fe同位素,暗示沉积时古海洋整体处于缺氧环境以避免Fe^(2+)发生氧化;4一些重要科学问题尚未解决,例如Si的主要来源、沉淀机制及条带成因等;5华北克拉通BIFs多形成于约2.54Ga,BIF类型、形成时代与富矿成因等问题有待深入研究。本文认为,加强国内外典型BIFs的对比研究并适当应用现代先进测试技术,有利于探索BIF沉积的精细过程及古老克拉通的早期演化。

Banded iron formations（ BIFs） were mainly formed in the early Precambrian（3. 8 ~ 1. 8Ga）; they record some important information about the evolution of early Earth and contain very large amounts of iron ores.This paper summarizes the significant advances and open issues on the BIF-related studies in China and abroad： 1the statistics and comparisons indicate that the BIF deposition was associated with momentous geological events,such as mantle plumes and crustal growth; 2 the REE and Nd isotope show that Fe precipitated from marine seawater with minor high-temperature hydrothermal component in the proportion of 1：1000; 3 most of BIFs have no Ce anomalies with enrichment in δ^（57）FeIRMM,implying that the paleo-ocean was in low abundances of O2 and thus Fe2 ＋could not be oxidized; 4 some key scientific problems have not been resolved,such as the source of Si,precipitation mechanism and genesis of bands; 5 BIFs in the North China Craton primarily occurred at about 2. 54Ga; however,some issues need to research deeply,such as the BIF types,formation ages and genesis of highgrade iron ores. We propose that the comparative studies on typical BIFs and applications of advanced measuring techniques are helpful to understand the precise procedures of BIF deposition and early evolution of old cratons.