Theoretical Predictions Versus Environmental Observations on Serpentinization Fluids: Lessons From the Samail Ophiolite in Oman

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 ( 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. Plain Language Summary The lithosphere is directly involved in the habitability of a planet. Interaction between water and rocks mobilizes nutrients and facilitates the transfer of energy from the lithosphere to the biosphere. Of all water and rock reactions on Earth, perhaps one of the most profound is serpentinization as it produces some of the most reduced and alkaline fluids on the planet. Fluids generated through serpentinization support microbial communities and thus are attractive for their potential to support life in the deep subsurface as well as in rocky bodies outside our own planet. Thermodynamic simulations allow pre