CONTRASTING MICROBE-MINERAL INTERACTIONS IN CONTINENTAL VS. SUBMARINE SERPENTINITES

Serpentinization is the aqueous alteration of ultramafic (Fe- and Mg-rich) rocks, resulting in secondary mineral assemblages of serpentine, brucite, iron oxyhydroxides and magnetite, talc, and possibly carbonate and silica-rich veins and other minor phases—all depending on the evolving pressure-temperature-composition of the system. The abiotic evolution of hydrogen and possibly organic compounds via serpentinization (McCollom and Bach, 2009) highlights the relevance of this geologic process to carbon and energy sources for the deep biosphere. Serpentinization may fuel life over long stretches of geologic time, throughout the global seabed and in exposed, faulted peridotite blocks (as at Lost City Hydrothermal Field, Kelley et al., 2005), and in obducted oceanic mantle units in ophiolites (e.g., Tiago et al., 2004).

In this work, I model serpentinizing fluid as an environmental niche. In terms of continental serpentinites, reported field data for high and moderate pH serpentinizing fluids were modeled from Cyprus, the Philippines, Oman, Northern California, New Caledonia, Yugoslavia, Portugal, Italy, Newfoundland Canada, New Zealand, and Turkey. In terms of submarine serpentinites, published data for modern and past serpentinizing systems are also considered, with sites as varied as the Lost City Hydrothermal Field and selected sites from Ocean Drilling Program Legs 125, 149, 153, and 195. I consider the implications of changing metabolic landscapes for subseafloor and obducted serpentinite-hosted biospheres.

References cited:

Kelley et al., 2005, Science 307:1428-1434.

McCollom and Bach, 2009, GCA 73:856–875.

Tiago et al., 2004, AEM 70(12):7378-7387.