Hydroxychloride‐Bearing Fluid Inclusions in Ultramafic Rocks From New Caledonia: Implications for Serpentinization in Saline Environments on Earth and Beyond. Issue 8 (26th August 2022)

• Record Type: Journal Article
• Authors: Zhang, Long; Wang, Qiang; Mikhailenko, Denis S.; Ding, Xing; Li, Wan‐Cai; Xian, Haiyang
• Is Part Of: Journal of geophysical research. Volume 127:Issue 8(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-08-26
• Subjects: serpentinization -- saline -- chlorine -- kuliginite -- fluid inclusions -- New Caledonia; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024508
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Serpentinization produces H2 and synthesizes CH4 that can support nonphotosynthetic habitability on Earth and possibly beyond. Although fluids on Earth and beyond that may participate in serpentinization are extensively saline with elevated levels of chlorine, chloride minerals are generally not considered to be a crucial component of serpentinization. In this study, we report the formation of kuliginite, a recently discovered hydroxychloride mineral with the ideal formula of Fe3 Mg(OH)6 Cl2, during internal serpentinization within olivine‐hosted fluid inclusions in ultramafic rocks from New Caledonia, southwest Pacific. It is inferred that kuliginite may form during serpentinization by Cl‐rich saline fluids under certain conditions on celestial bodies, which is largely unrevealed due to our insufficient knowledge about kuliginite. As a mineral containing ∼57 wt.% FeO that is mainly ferrous, kuliginite, even in minor amounts, may play an important role in iron partitioning during serpentinization, with a great influence on the production of H2 and synthesis of CH4 . In a word, stabilization of kuliginite retards iron oxidation, whereas further hydration of kuliginite supplements canonical pathways of iron oxidation. In addition, as a hydroxychloride, kuliginite may have a significant weight in the chlorine budget of serpentinite. Therefore, kuliginite in the serpentinized fluid inclusions presented in this study may have general implications for serpentinization in certain saline environments on Earth and beyond, which needs to be further explored in the future. Plain Language Summary: Serpentinization represents the hydration of mantle rocks uplifted to the surface into serpentine‐dominated rocks. It produces hydrogen and synthesizes methane that can be utilized as energy by chemosynthetic microbes to further support a nonphotosynthetic habitat. Generation of hydrogen from water during serpentinization is caused by the oxidation of iron, which is dictated by iron distribution between newly formed minerals. In this study, kuliginite, a recently discovered chloride mineral with the ideal formula of Fe3 Mg(OH)6 Cl2, is shown to form during serpentinization in mantle rocks from New Caledonia, southwest Pacific. It is proposed that kuliginite may be produced during serpentinization in certain saline environments on Earth and beyond. As kuliginite is highly enriched in iron, its presence during serpentinization can significantly influence iron distribution and hydrogen generation. Future studies are expected to identify more kuliginite and better understand the role of chlorine during serpentinization. Key Points: Kuliginite, a recently discovered hydroxychloride with the ideal formula of Fe3 Mg(OH)6 Cl2, was found in serpentinized fluid inclusions Kuliginite may form during serpentinization in certain saline environments on Earth and beyond Kuliginite formation can greatly influence iron partitioning and hydrogen/methane generation during serpentinization