Shishun Wang, Chunhui Tao, Shili Liao, Mingcheng Cai, Tao Wu, Mingxu Wang
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引用次数: 0
Abstract
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.
期刊介绍：
The Journal of Geophysical Research: Solid Earth serves as the premier publication for the breadth of solid Earth geophysics including (in alphabetical order): electromagnetic methods; exploration geophysics; geodesy and gravity; geodynamics, rheology, and plate kinematics; geomagnetism and paleomagnetism; hydrogeophysics; Instruments, techniques, and models; solid Earth interactions with the cryosphere, atmosphere, oceans, and climate; marine geology and geophysics; natural and anthropogenic hazards; near surface geophysics; petrology, geochemistry, and mineralogy; planet Earth physics and chemistry; rock mechanics and deformation; seismology; tectonophysics; and volcanology.
JGR: Solid Earth has long distinguished itself as the venue for publication of Research Articles backed solidly by data and as well as presenting theoretical and numerical developments with broad applications. Research Articles published in JGR: Solid Earth have had long-term impacts in their fields.
JGR: Solid Earth provides a venue for special issues and special themes based on conferences, workshops, and community initiatives. JGR: Solid Earth also publishes Commentaries on research and emerging trends in the field; these are commissioned by the editors, and suggestion are welcome.
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