Banded iron formations (BIFs) were deposited before and concurrent with the Great Oxidation Event at ∼2.33 Ga. They provide useful archives that document the transformation of the Precambrian hydrosphere from anoxic to progressively oxygenated conditions. Their formation involves removal of oceanic Fe by either inorganic or biologically promoted Fe²⁺ oxidation, or both. To evaluate depositional settings, elemental sources that affect seawater chemistry, and oxidation pathways, we present the first combined highly siderophile element (HSE) and Fe-Os isotope study for the ∼2.7 Ga Temagami BIF, Abitibi Greenstone Belt, Ontario (Canada). HSE abundances and ¹⁸⁷Os/¹⁸⁸Os ratios show no systematic variation between alternating magnetite and (meta)chert bands of the Temagami BIF. Whereas HSE concentrations mostly resemble modern crustal values, present-day ¹⁸⁷Os/¹⁸⁸Os ratios range from ∼0.17 to ∼10.8. Magnetite samples define a regression line corresponding to an age of 2661 ± 126 Ma. A chondrite-like ¹⁸⁷Os/¹⁸⁸Os initial value is in agreement with earlier studies on Neoarchean marine sediments and is thought to reflect seawater composition, which, unlike modern oceans, is dominated by mantle-like ¹⁸⁷Os inventory most likely derived from deep-sea hydrothermal vents. Our δ⁵⁶Fe data vary from about +0.6‰ to +0.9‰ and define a sawtooth-like pattern between alternating magnetite and (meta)chert layers. Partial oxidation of hydrothermally sourced Fe(II) and a lack of microbially mediated dissimilatory iron reduction provide the most plausible explanation for the positive δ⁵⁶Fe values. Notably, our δ⁵⁶Fe data for Temagami are in accord with trends defined by literature results for other Algoma-type BIFs that were deposited throughout the Archean.

中文翻译：

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加拿大 Temagami 铁层中的高度亲铁元素和耦合的 Fe-Os 同位素特征：新太古代海水化学和地球氧化历史的可能特征

带状铁地层 (BIFs) 在大氧化事件发生之前和同时沉积在~2.33 Ga。它们提供了有用的档案，记录了前寒武纪水圈从缺氧条件到逐渐氧化条件的转变。它们的形成涉及通过无机或生物促进的 Fe ²⁺氧化或两者兼而有之，去除海洋中的 Fe 。为了评估沉积环境、影响海水化学的元素来源和氧化途径，我们首次针对加拿大安大略省阿比提比绿岩带的 ~2.7 Ga Temagami BIF 进行了高亲铁元素 (HSE) 和 Fe-Os 同位素组合研究。HSE 丰度和¹⁸⁷ Os/ ¹⁸⁸Os 比率显示 Temagami BIF 的交替磁铁矿和（元）燧石带之间没有系统变化。虽然 HSE 浓度大多类似于现代地壳值，但当今¹⁸⁷ Os/ ¹⁸⁸ Os 的比率范围从 ~0.17 到 ~10.8。磁铁矿样品定义了对应于 2661 ± 126 Ma 年龄的回归线。类似球粒陨石的¹⁸⁷ Os/ ¹⁸⁸ Os 初始值与早期对新太古代海洋沉积物的研究一致，被认为反映了海水成分，与现代海洋不同，海水成分以类似地幔的¹⁸⁷ Os 存量为主，最有可能来自深海海洋热液喷口。我们的δ ⁵⁶Fe 数据从大约 +0.6‰ 到 +0.9‰ 变化，并在交替的磁铁矿和（变）燧石层之间定义了锯齿状图案。水热来源的 Fe(II) 的部分氧化和缺乏微生物介导的异化铁还原为正 δ ⁵⁶ Fe 值提供了最合理的解释。值得注意的是，我们的 Temagami δ ⁵⁶ Fe 数据与沉积在整个太古代的其他 Algoma 型 BIF 的文献结果所定义的趋势一致。