Seafloor massive sulfide (SMS) deposits in different geological settings can have variable magnetic mineralogy, but the mechanism and implications of their spatiotemporal diversity are poorly understood. Based on seabed shallow drilling and surficial sampling of the Yuhuang hydrothermal field, Southwest Indian Ridge, we investigate here whether ubiquitous oxidative weathering affects the magnetic properties of SMS deposits. Microscopic observation and ferrous iron concentrations reveal that seafloor SMS deposits are extensively oxidized; subseafloor SMS deposits are relatively fresh, but oxidation initiates immediately after sample recovery. Negative frequency dependence of magnetic susceptibility likely due to measurement eddy currents is observed for fresh samples but not for oxidized ones, which suggests that oxidative weathering reduces the electromagnetic detectability of SMS deposits in geophysical investigations. Pyrrhotite (and probably other magnetic iron sulfide minerals), magnetite, and hematite are recognized as dominating magnetic (ferromagnetic, sensu lato) minerals in SMS deposits. Electron and quantum diamond microscope observations reveal pyrrhotite mineralization from high-temperature reducing hydrothermal fluids, while iron-oxides are mostly oxidation products of primary sulfides. Oxidative weathering modifies paleomagnetic records of SMS deposits. Bulk magnetic parameters vary systematically with enhanced oxidation degree. Temperature-dependent magnetic measurements are useful tools for distinguishing the oxidation state of SMS deposits. Overall, these findings explain magnetic mineral variability in SMS deposits, linking mineral magnetic properties with seafloor geophysical investigations. Mineral magnetism can also be a redox state proxy for tracing natural and artificial environmental fluctuations in seafloor hydrothermal fields, inspiring novel interdisciplinary research to understand interactions in the dynamic Earth System.

中文翻译：

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海底块状硫化物矿床的氧化还原敏感矿物磁特征


不同地质环境中的海底块状硫化物 （SMS） 矿床可能具有可变的磁性矿物学，但对其时空多样性的机制和影响知之甚少。基于西南印度海脊玉皇热液田的海底浅层钻探和地表取样，我们研究了无处不在的氧化风化作用是否影响 SMS 矿床的磁性。显微镜观察和亚铁浓度表明，海底 SMS 矿床被广泛氧化;海底 SMS 沉积物相对较新鲜，但在样品回收后立即开始氧化。对于新样品，可能由于测量涡流而观察到磁化率的负频率依赖性，但在氧化样品中未观察到，这表明氧化风化降低了地球物理研究中 SMS 矿床的电磁可探测性。磁黄铁矿（可能还有其他磁性硫化铁矿物）、磁铁矿和赤铁矿被认为是 SMS 矿床中占主导地位的磁性（铁磁性、sensu lato）矿物。电子和量子金刚石显微镜观察揭示了高温还原热液流体中的磁黄铁矿矿化，而氧化铁主要是初级硫化物的氧化产物。氧化风化改变了 SMS 矿床的古地磁记录。体磁参数随着氧化程度的增加而系统地变化。与温度相关的磁性测量是区分 SMS 沉积物氧化态的有用工具。总体而言，这些发现解释了 SMS 矿床中的磁性矿物变化，将矿物磁性与海底地球物理研究联系起来。 矿物磁学也可以作为追踪海底热液场中自然和人工环境波动的氧化还原状态代理，激发新的跨学科研究来理解动态地球系统中的相互作用。