条带状铁建造（BIF）的形成时代及其研究方法

对条带状铁建造（BIF）进行精确的年代学约束，具有非常重要的科学意义，可以获得BIF的时间分布趋势，反映对应时代的大气和海洋环境，准确建立与重大地质事件的对应关系，为铁建造的成因提供依据。本文在综合前人资料的基础上，重新绘制了全球BIF形成时代的分布图，结果表明BIF在3.6～1.6 Ga连续分布，在2.8～2.7 Ga、 2.5～2.4 Ga、 1.9～1.8 Ga的3个区间范围内形成高峰；Algoma型BIF主要集中于中-晚太古代，而Superior型BIF主要出现在古元古代。本文重点对前人关于BIF年代学的测试方法及其应用进行了介绍和评述，结果表明目前锆石U-Pb测年法依然为主要手段，而Sm-Nd等时线法和Re-Os等时线法尽管有效，但直接测定BIF条带的Sm-Nd等时线和磁铁矿的Re-Os等时线年龄仍存在较大问题，但可用来反映物质的来源以及后期构造热事件的改造等问题，而采取BIF相关单元的年龄来间接代表BIF的形成年龄是目前较为成熟的方法，其中测定铁建造火山岩夹层锆石U-Pb年龄是国际上测定BIF时代常用的手段。

The formation era of BIF and its research methods

To give precise chronology constraints on BIF has very important scientific significance, which can obtain the trend of the time distribution of BIF, reflect the atmospheric and oceanic environment of the corresponding age, establish a corresponding relation with major geological events accurately and provide the basis for the genesis of iron formation. Based on integrating predecessors material, we repaint the formation era distribution diagram of BIF. The results show that BIF has a continuous distribution from 3.6 Ga to 1.6 Ga, forms a peak within three interval range: 2.8～2.7 Ga, 2.5～2.4 Ga, 1.9～1.8 Ga; Algoma-type BIF is dominant in Meso-Neoarchean, whereas Superior-type BIF is much more common in Paleoproterozoic. At the same time, we mainly introduce and review predecessors articles about test methods of BIF chronology and their application, which indicate that at present the zircon U-Pb method is still a main approach, whereas the Sm-Nd isochrone and Re-Os isochrone methods are still effective, however direct measurement of the Sm-Nd isochrone age about BIF mesobands and the Re-Os isochrone age about magnetite still have considerable problems, but which can reflect some other aspects of problems such as the origin of material, the transformation of later structure hot events. Taking the age of relevant units of BIF on behalf of the formation age of BIF indirectly is the mature method at the present, therein determination of the zircon U-Pb age about volcanics interbedded with iron formations is the common means to determine the age of BIF internationally.