EVOLVING GEOCHEMISTRY OF SERPENTINITE-HOSTED WATERS

Serpentinization is a long duration, expansive geologic process exhibiting punctuated equilibrium characteristics. Olivine and pyroxene minerals in parent rocks alter to serpentine-dominated assemblages; overall, ferrous iron is oxidized and hydrogen in molecular water is reduced to diatomic hydrogen, generating daughter materials generally more hydrated, oxidized, and diverse when compared to parent materials. Depending on tectonic history and weathering patterns, sequential, distinct periods of water-rock interaction imprint mineralogically in the host rock and drive changes in the geochemistry of through-flowing waters. I propose that these be viewed in the context of quasi-stable systems within a punctuated equilibrium framework. Geochemical modeling results support this framework, and field and analytical observations (XRD data, thin section analyses) of Coast Range Ophiolite ultramafic units (Lower Lake, CA locality) serve as a case study. Wide-reaching implications for elemental cycling, gas evasion, and support of the resident chemosynthetic biosphere are considered.