Courtney-Davies Liam, Fiorentini Marco, Dalstra Hilke, Hagemann Steffen, Ramanaidou Erick, Danišik Martin, Evans Noreen J, Rankenburg Kai, McInnes Brent I A
John de Laeter Centre, Curtin University, Perth, WA 6845, Australia.
Centre for Exploration Targeting, School of Earth Sciences, The University of Western Australia, Perth, WA 6009, Australia.
Proc Natl Acad Sci U S A. 2024 Jul 30;121(31):e2405741121. doi: 10.1073/pnas.2405741121. Epub 2024 Jul 23.
Banded iron formations (BIFs) archive the relationship between Earth's lithosphere, hydrosphere, and atmosphere through time. However, constraints on the origin of Earth's largest ore deposits, hosted by BIFs, are limited by the absence of direct geochronology. Without this temporal context, genetic models cannot be correlated with tectono-thermal and atmospheric drivers responsible for BIF upgrading through time. Utilizing in situ iron oxide U-Pb geochronology, we provide a direct timeline of events tracing development of all the giant BIF-hosted hematite deposits of the Hamersley Province (Pilbara Craton, Western Australia). Direct dating demonstrates that the major iron ore deposits in the region formed during 1.4 to 1.1 Ga. This is one billion to hundreds of millions of years later than previous age constraints based upon 1) the presence of hematite ore clasts in conglomerate beds deposited before ~1.84 Ga, and 2) phosphate mineral dating, which placed the onset of iron mineralization in the Province at ~2.2 to 2.0 Ga during the great oxidation event. Dating of the hematite clasts verified the occurrence of a ~2.2 to 2.0 Ga event, reflecting widespread, but now largely eroded iron mineralization occurring when the Pilbara and Kaapvaal cratons were proximal. No existing phosphate mineral dates overlap with obtained hematite dates and therefore cannot be related to hematite crystallization and ore formation. New geochronology conclusively links all major preserved hematite deposits to a far younger (1.4 to 1.1 Ga) formation period, correlated with the amalgamation of Australia following breakup of the Columbia supercontinent.
条带状铁建造（BIFs）记录了地球岩石圈、水圈和大气圈随时间的关系。然而，由BIFs承载的地球上最大的矿床成因受到缺乏直接地质年代学的限制。没有这种时间背景，成因模型就无法与随时间导致BIF升级的构造-热和大气驱动因素相关联。利用原位氧化铁铀-铅地质年代学，我们提供了一个直接的事件时间线，追踪了哈默斯利省（西澳大利亚皮尔巴拉克拉通）所有巨型BIF-hosted赤铁矿矿床的发育过程。直接测年表明，该地区的主要铁矿床形成于14亿至11亿年前。这比基于以下两点的先前年龄限制晚了10亿至数亿年：1）在约18.4亿年前沉积的砾岩床中存在赤铁矿矿屑；2）磷酸盐矿物测年，该测年将该省铁矿化的开始时间定在大氧化事件期间的约22亿至20亿年前。对赤铁矿矿屑的测年证实了约22亿至20亿年前事件的发生，反映了当时皮尔巴拉和卡普瓦尔克拉通相邻时广泛但现已大部分被侵蚀的铁矿化。现有的磷酸盐矿物测年结果与获得的赤铁矿测年结果没有重叠，因此与赤铁矿结晶和矿石形成无关。新的地质年代学最终将所有主要保存下来的赤铁矿矿床与一个年轻得多（14亿至11亿年前）的形成时期联系起来，这与哥伦比亚超大陆解体后澳大利亚的合并相关。
