9 Reviews in Mineralogy & Geochemistry Vol. 76 pp. 311-350, 2013 Copyright © Mineralogical Society of America 1529-6466/13/0076-0009$05.00 http://dx.doi.org/10.2138/rmg.2013.76.9 Thermodynamics of Organic Transformations in Hydrothermal Fluids Everett L. Shock 1,2 , Peter Canovas 1 , Ziming Yang 2 , Grayson Boyer 2 , Kristin Johnson 2 , Kirtland Robinson 2 , Kristopher Fecteau 2 , Todd Windman 2 , Alysia Cox 1 GEOPIG 1 School of Earth & Space Exploration 2 Department of Chemistry & Biochemistry Arizona State University Tempe, Arizona 85287, U.S.A. Everett.Shock@asu.edu MESSAGES FROM NATURE Hydrothermal luids obtain organic compounds through diverse pathways. In submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal luids through water-rock reactions. Microbes inhabiting hydrothermal systems produce metabolites that enter the luids, and cells can be carried into the reaction zones by circulating luids and pyrolyzed. Analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant- and soil-derived organic compounds from the surface. In addition, hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds. When sedimentary rocks are present, ancient biogenic organic matter can be mobilized or transformed by hot luids. These transformations accompany the generation of petroleum, coal, and other fossil fuels, suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins. Likewise, some types of ore deposition are accompanied by transformations of organic compounds, and metal-organic complexes may be involved in enhancing the transport of metals in ore-forming and other crustal luids. With these thoughts in mind, this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed. ORGANIC INVENTORY OF HYDROTHERMAL FLUIDS Methane can be generated biotically and abiotically from organic or inorganic reactants, and since it lacks a carbon-carbon bond, some researchers would not consider it to be an or- ganic compound. Nevertheless, more data exist for methane in hydrothermal luids than for any organic compound that its the deinition. Methane has been quantiied in continental and submarine hydrothermal luids, fumarolic gases associated with hydrothermal systems, oil- ield brines, deep luids in sedimentary basins and igneous basement rocks, luids associated with active serpentinization, and luid inclusions in minerals from ore deposits, sedimentary basins, and deep crustal settings (recent examples include: Sherwood-Loller et al. 2002; Tassi et al. 2003, 2005a,b, 2007, 2012a,b,c; Potter et al. 2004; Fiebig et al. 2004, 2007, 2009, Cruse and Seewald 2006, 2010; Ikorsky and Avedisyan 2007; Taran et al. 2010; Cinti et al. 2011; Nivin 2011; McLin et al. 2012; Magro et al. 2013). Typical abundances in submarine hy-