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<p>Banded Iron Formations (BIFs), tuffaceous deposits, and chert commonly co-occur in Archean volcano-sedimentary sequences, indicating a complex genetic relationship influenced by hydrothermal, volcanic, and sedimentary processes in greenstone belts. These lithologies often form in submarine hydrothermal settings, reflecting the interaction of volcanic activity, ocean chemistry, and biological influences. Understanding their genetic relationships is crucial for reconstructing paleoenvironmental conditions, determining ore-forming processes, and exploring mineral deposits. The genetic link between BIF, tuff, and chert in volcano-sedimentary environments reflects a dynamic interplay of volcanic input, hydrothermal activity, and ocean chemistry. This study examines their interconnections by field based approach. Archaean greenstone belts also often contain thin successions of immature clastic rocks broadly referred to as greywackes (meta-graywackes after metamorphism). These units are central to reconstructing Archean sedimentary systems, provenance, and tectonic settings, but their highly variable texture, mixed provenance signature, and overprinting by hydrothermal alteration and metamorphism produce persistent ambiguities—the “greywacke puzzle.” Greywacke are easily confused with metamorphosed mafic/ultramafic-derived lithologies and with meta-basics/volcaniclastic rocks. The role of hydrothermal exhalations, silica precipitation mechanisms, and volcanic inputs in the formation of these lithologies is discussed in detail, providing insights into early Earth conditions. Tuffaceous layers interbedded with BIFs indicate episodic volcanic activity. Volcanic ash contributes Fe, Si, and trace elements to the ocean, enhancing chemical precipitation. Pyroclastic inputs provide reactive surfaces for Fe and silica precipitation, influencing BIF mineralogy. Archaean Earth was hotter (with average sea water temperature &gt; 65&#xa0;°C) than present, hence freely available hydrothermal Fe-rich input, with iron sourced from deep-sea vents could transport dissolved silica, leading to chert precipitation. Chert bands in BIFs may form due to fluctuations in hydrothermal activity, affecting Fe-Si ratios in seawater. BIF and chert deposition also coincides with episodic oxygenation events, promoting Fe oxidation. Archaean prokaryotic cyanobacteria also play a role in silica and Fe precipitation, leading to form laminations in BIF and chert. The transition from Fe-rich to Si-rich layers reflects variations in ocean chemistry, hydrothermal flux, and biological activity.</p>

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Genetic link between banded iron formation (BIF), tuff, and chert in a Volcano-Sedimentary environment of archaean greenstone belts

  • 期刊论文

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  • 发表日期：

    2025年12月5日

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  • Sukanta Goswami

摘要

Banded Iron Formations (BIFs), tuffaceous deposits, and chert commonly co-occur in Archean volcano-sedimentary sequences, indicating a complex genetic relationship influenced by hydrothermal, volcanic, and sedimentary processes in greenstone belts. These lithologies often form in submarine hydrothermal settings, reflecting the interaction of volcanic activity, ocean chemistry, and biological influences. Understanding their genetic relationships is crucial for reconstructing paleoenvironmental conditions, determining ore-forming processes, and exploring mineral deposits. The genetic link between BIF, tuff, and chert in volcano-sedimentary environments reflects a dynamic interplay of volcanic input, hydrothermal activity, and ocean chemistry. This study examines their interconnections by field based approach. Archaean greenstone belts also often contain thin successions of immature clastic rocks broadly referred to as greywackes (meta-graywackes after metamorphism). These units are central to reconstructing Archean sedimentary systems, provenance, and tectonic settings, but their highly variable texture, mixed provenance signature, and overprinting by hydrothermal alteration and metamorphism produce persistent ambiguities—the “greywacke puzzle.” Greywacke are easily confused with metamorphosed mafic/ultramafic-derived lithologies and with meta-basics/volcaniclastic rocks. The role of hydrothermal exhalations, silica precipitation mechanisms, and volcanic inputs in the formation of these lithologies is discussed in detail, providing insights into early Earth conditions. Tuffaceous layers interbedded with BIFs indicate episodic volcanic activity. Volcanic ash contributes Fe, Si, and trace elements to the ocean, enhancing chemical precipitation. Pyroclastic inputs provide reactive surfaces for Fe and silica precipitation, influencing BIF mineralogy. Archaean Earth was hotter (with average sea water temperature > 65 °C) than present, hence freely available hydrothermal Fe-rich input, with iron sourced from deep-sea vents could transport dissolved silica, leading to chert precipitation. Chert bands in BIFs may form due to fluctuations in hydrothermal activity, affecting Fe-Si ratios in seawater. BIF and chert deposition also coincides with episodic oxygenation events, promoting Fe oxidation. Archaean prokaryotic cyanobacteria also play a role in silica and Fe precipitation, leading to form laminations in BIF and chert. The transition from Fe-rich to Si-rich layers reflects variations in ocean chemistry, hydrothermal flux, and biological activity.