DETERMINING THE DEGREE OF SERPENTINIZATION OF CORED ROCKS IN THE COAST RANGE OPHIOLITE IN LOWER LAKE, CA, USA

The reaction of water with rocks from planetary subsurfaces (i.e., silicate rich mantles) forms new mineral assemblages rich in serpentine; for this reason, detection of the mineral serpentine is a signal of the past presence of liquid water and possible chemosynthetic microbial ecosystems. Serpentinization can power living systems because olivine-rich, mantle-type parent rocks interact with water, and as minerals transform, the reactions also release hydrogen and complex organics that serve as reactants for microbial metabolic reactions. These particular rocks have been also detected on Mars (Ehlmann et al., 2010) and an argument has been made for chemosynthetic life on Mars (Schulte et al., 2006), causing interest from many geologists. In this study, serpentinite samples were obtained at the Coast Range Ophiolite Microbial Observatory (CROMO), a research site located at McLaughlin Natural Reserve in Lower Lake, California. The samples included cored rocks from Homestake Mining Co., Inc. at site M81-313 (88^o 57.4’ NW, 7^o 15.4’SW) and surface samples at the CROMO were collected in summer 2016 for context. The rocks were analyzed using x-ray diffraction (XRD) and diffractograms were interpreted using peak-matching software (X-powder, xpowder.com), to give a semi-quantitative analysis of the minerals. Cored samples had notable variation in the proportion of serpentine group minerals, ranging from ~9% to ~60%. Two of the samples tested did not have any of serpentine group minerals present, meaning there was a change in lithology (likely altered mafic material) at that depth. Consequently, these findings suggest that deep, dark, chemically-driven habitat exists in unconventional places (serpentinite-dominated subsurface environments on Earth, Mars, and perhaps other planetary bodies) that were thought to be unsuitable for life in the past.