@article{560b43da5b0f43f7bf7f76ce9f28eb2b,
title = "Theoretical Predictions Versus Environmental Observations on Serpentinization Fluids: Lessons From the Samail Ophiolite in Oman",
abstract = "Thermodynamic calculations provide valuable insights into the reactions that drive the profound fluid transformations during serpentinization, where surface fluids are transformed into some of the most reduced and alkaline fluids on Earth. However, environmental observations usually deviate from thermodynamic predictions, especially those occurring at low temperatures where equilibrium is slowly reached. In this work, we analyzed 138 low-temperature (<40°C) fluids from the Samail ophiolite in Oman to test thermodynamic predictions with environmental observations. Four fluid types were identified through this work. (i) Type 1 circumneutral (pH 7–9) fluids result from fluid interactions with serpentinized rocks common in the shallow subsurface. (ii) Fluids with pH ranging from 9 to 11 and low Si concentrations are products of intermediate stages of serpentinization. (iii) Type 2 hyperalkaline (pH > 11) fluids approach equilibrium with diopside, and with serpentine and brucite actively forming during advanced stages of serpentinization. Lastly, (iv) most fluids sampled in this work deviate from predicted equilibrium compositions and depict various degrees of mixing between Type 1 and 2 fluids. Mixed fluids fall within the same pH range but have considerably higher dissolved Si than intermediate-type fluids. Hyperalkaline fluids exhibit variable degrees of mixing despite maintaining pH > 11, implying strong buffering capacity of serpentinization-generated fluids. Overall, this work demonstrates that predicted and measured compositions of serpentinization-derived fluids can be reconciled using a combination of equilibrium and fluid-transport simulations. This work substantiates these calculations as useful tools in exploring serpentinization reactions in continents and perhaps in other low-temperature environments on Earth and beyond.",
keywords = "Geochemical modeling, Oman ophiolite, hyperalkaline fluids, serpentinization, spring chemistry, thermodynamics",
author = "Leong, {J. A.M.} and Howells, {A. E.} and Robinson, {K. J.} and A. Cox and Debes, {R. V.} and K. Fecteau and P. Prapaipong and Shock, {E. L.}",
note = "Funding Information: Samples used in this study were gathered with the help of Peter Kelemen, Juerg Matter, Amelia Paukert Vankeuren, Lisa Streit‐Falk, Peter Canovas, Jeff Havig, and Peter Marsala. Thanks to Prof. Sobhi Nasir of Sultan Qaboos University for help with logistics in Oman. We also would like to thank Tracy Lund, Natasha Zolotova, and Roy Erikson for help in analysis of fluid samples at the ASU GEOPIG laboratory, W.M. Keck Foundation Laboratory for Environmental Biogeochemistry, and Goldwater Environmental Laboratory (the latter two now merged as the Metals, Environmental and Terrestrial Analytical Laboratory [METAL]). Thanks also to Tucker Ely, Vincent Milesi, and Grayson Boyer for helpful discussions on computational tools used in this study. We would like to thank editor Stephen Parman, the anonymous associate editors, Alexis Templeton, and an anonymous reviewer for their helpful and insightful suggestions and reviews. This work was supported by NASA Exobiology grant NNX12AB38G, the NASA Astrobiology Institute Rock‐Powered Life (RPL) and Exploring Ocean Worlds (ExOW) projects, and NSF grant EAR‐1515513. Funding Information: Samples used in this study were gathered with the help of Peter Kelemen, Juerg Matter, Amelia Paukert Vankeuren, Lisa Streit-Falk, Peter Canovas, Jeff Havig, and Peter Marsala. Thanks to Prof. Sobhi Nasir of Sultan Qaboos University for help with logistics in Oman. We also would like to thank Tracy Lund, Natasha Zolotova, and Roy Erikson for help in analysis of fluid samples at the ASU GEOPIG laboratory, W.M. Keck Foundation Laboratory for Environmental Biogeochemistry, and Goldwater Environmental Laboratory (the latter two now merged as the Metals, Environmental and Terrestrial Analytical Laboratory [METAL]). Thanks also to Tucker Ely, Vincent Milesi, and Grayson Boyer for helpful discussions on computational tools used in this study. We would like to thank editor Stephen Parman, the anonymous associate editors, Alexis Templeton, and an anonymous reviewer for their helpful and insightful suggestions and reviews. This work was supported by NASA Exobiology grant NNX12AB38G, the NASA Astrobiology Institute Rock-Powered Life (RPL) and Exploring Ocean Worlds (ExOW) projects, and NSF grant EAR-1515513. Publisher Copyright: {\textcopyright} 2021. American Geophysical Union. All Rights Reserved.",
year = "2021",
month = apr,
doi = "10.1029/2020JB020756",
language = "English (US)",
volume = "126",
journal = "Journal of Geophysical Research: Solid Earth",
issn = "2169-9313",
publisher = "Wiley-Blackwell",
number = "4",
}