Neoproterozoic iron formations are exposed in the Wadi Hamama area (Egypt) in the northwestern part of the Arabian–Nubian Shield. Mafic and felsic volcanic and volcaniclastic rocks of an intra-oceanic island-arc setting host multiple, thin iron-formation units. Major element compositions of the iron formation confirm a low detrital input, whereas the rare-earth elements and Y data suggest deposition related to an influx of low-temperature hydrothermal fluids. Unlike most Neoproterozoic banded iron formations, but similar to other iron-formation occurrences from the Arabian–Nubian Shield, the Nd isotopic compositions of the Wadi Hamama iron formations are predominantly mantle-like. SIMS U–Pb zircon ages of the host volcaniclastic units indicate that the age of iron-formation deposition is ca. 695 Ma, which is within the Sturtian epoch that is presumed to be a glacial event of global extent. Nevertheless, there is no robust evidence of any influence of Sturtian glaciation in the Arabian–Nubian Shield. Our results rather suggest that the iron formations in the area may have formed as low-temperature exhalites on the floor of an island-arc basin. The iron formations were deposited during periods of volcanic quiescence, with metals having been derived during low-temperature pervasive hydrothermal alteration of volcanic and volcaniclastic rocks exposed at the seafloor–seawater interface. Precipitation took place due to mixing of metal-bearing hydrothermal fluids and cold, oxygenated seawater. There is no need to invoke possible effects of global glaciation to explain the origin of the Sturtian-aged iron formations in the shield. Our study thus suggests that not all Neoproterozoic iron formations are necessarily linked to glacial events as the Hamama deposit represents a non-Rapitan exhalative iron formation.

中文翻译：

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并非所有的新元古代铁地层都是冰川成因的：来自阿拉伯-努比亚地盾的斯图尔蒂安时代非拉皮坦喷气铁地层

新元古代铁地层出露在阿拉伯-努比亚地盾西北部的 Wadi Hamama 地区（埃及）。大洋内岛弧环境中的镁铁质和长英质火山岩和火山碎屑岩拥有多个薄铁形成单元。铁地层的主要元素组成证实了低碎屑输入，而稀土元素和 Y 数据表明沉积与低温热液流体的流入有关。与大多数新元古代带状铁地层不同，但与阿拉伯-努比亚地盾的其他铁地层产地类似，Wadi Hamama 铁地层的 Nd 同位素组成主要是地幔状。寄主火山碎屑单元的 SIMS U-Pb 锆石年龄表明铁形成沉积的年龄约为 695 马，这是在 Sturtian 时代，被认为是全球范围的冰川事件。然而，没有强有力的证据表明阿拉伯-努比亚地盾中的斯图尔特冰川有任何影响。我们的研究结果表明，该地区的铁矿层可能是岛弧盆地底部的低温喷出物。铁地层是在火山静止期间沉积的，金属是在暴露于海底 - 海水界面的火山和火山碎屑岩的低温普遍热液蚀变中衍生出来的。降水是由于含金属的热液与寒冷的含氧海水混合而发生的。无需援引全球冰川作用的可能影响来解释地盾中 Sturtian 时代铁层的起源。