60-36 Assessing Fluid Composition Changes Through Reaction with Serpentinized Peridotites

Session: 2YC and 4YCU Geoscience Student Research Poster Showcase

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The Cenozoic has seen significant changes in the magnesium and calcium ratios in seawater. Different hypothesis exist for of these changes. One overlooked source of Mg are peridotites exposed in ultra-slow spreading ridges. Peridotites are unstable in these conditions and their olivine and pyroxenes react with water to form an array of secondary minerals, most notably serpentinite, in a process called serpentinization. Ocean drillcore samples show that brucite contents increases with depth and is almost non-existent in samples collected near or at the seafloor. Brucite is undersaturated in fluids close to neutral pH (like seawater). These suggest that serpentinite alteration may be a contributor of the increasing magnesium concentrations in Cenozoic seawater. ​ This project focused on reacting serpentinized peridotites with and without brucite with water and evaluate fluid chemistry changes over time. Fluids near neutral pH are undersaturated in brucite and brucite releases OH- when dissolved and so should raise the fluid’s pH significantly. The goal being to see which samples contain brucite and what geochemical signatures can be used to identify the process of dissolution of brucite in water from these samples. Samples identified to have an abundance of brucite will be used in other projects of this lab to quantify the magnesium exchange between fluids and peridotite during serpentinization.​ We find that changes in pH and dissolved Mg2+ within fluid show a distinct signature that can be used to identify the dissolution of brucite from ophiolitic peridotites altered by fluid interactions. Using our methods, it can be seen that specific samples in our sample group contain brucite in their mineralogies and that this alteration process favors the dissolution of brucite over serpentinite into water.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8598

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