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- Title
Controls on Mineral Formation in High pH Fluids From the Lost City Hydrothermal Field.
- Authors
Aquino, Karmina A.; Früh‐Green, Gretchen L.; Bernasconi, Stefano M.; Bontognali, Tomaso R. R.; Foubert, Anneleen; Lang, Susan Q.
- Abstract
Although the serpentinite‐hosted Lost City hydrothermal field (LCHF) was discovered more than 20 years ago, it remains unclear whether and how the presence of microbes affects the mineralogy and textures of the hydrothermal chimney structures. Most chimneys have flow textures comprised of mineral walls bounding paleo‐channels, which are preserved in inactive vent structures to a varying degree. Brucite lines the internal part of these channels, while aragonite dominates the exterior. Calcite is also present locally, mostly associated with brucite. Based on a combination of microscopic and geochemical analyses, we interpret brucite, calcite, and aragonite as primary minerals that precipitate abiotically from mixing seawater and hydrothermal fluids. We also observed local brucite precipitation on microbial filaments and, in some cases, microbial filaments may affect the growth direction of brucite crystals. Brucite is more fluorescent than carbonate minerals, possibly indicating the presence of organic compounds. Our results point to brucite as an important substrate for microbial life in alkaline hydrothermal systems. Plain Language Summary: Water‐serpentinite reactions at the Lost City hydrothermal field (LCHF) are considered similar to the interactions between seawater and volcanic rocks of the early Earth. The vent fluids that form as a result of this interaction are rich in organic compounds that serve as food and hydrogen that provides energy for microbial life. Systems such as Lost City are ideal sites for investigating processes relevant to early life on Earth. Dense microbial communities live in the mineral structures that form from mixing between vent fluids and seawater at the LCHF. The effect of these microbial inhabitants on the mineralogy and textures of the hydrothermal chimneys is still unknown. This study aims to better understand the mineralogy of the hydrothermal chimneys at Lost City and the relationships between microbes and minerals. Calcite and brucite form in the interior of the chimneys, while aragonite forms on the exterior. Brucite forms inorganic mineral membranes that bound cavities where microbes may live. Unlike calcite and aragonite, brucite is spatially closely associated with microbial activity. Key Points: Lost City hydrothermal chimneys preserve flow textures defined by mineral membranes bounding paleo‐channels and form a network of cavitiesThe backbone of the chimney structure is initially brucite. Carbonates precipitate on brucite as the chimneys continue to formBrucite is the preferred substrate for the growth of microbial biofilms within the chimneys
- Subjects
CALCITE; CARBONATE minerals; MINERALS; BRUCITE; CHIMNEYS; VOLCANIC ash, tuff, etc.
- Publication
Geochemistry, Geophysics, Geosystems: G3, 2024, Vol 25, Issue 2, p1
- ISSN
1525-2027
- Publication type
Article
- DOI
10.1029/2023GC011010