Carbon Transformations in Seafloor Serpentinization Systems

Niya Grozeva, Ph.D., 2018
Frieder Klein, Co-Advisor
Jeffrey Seewald, Co-Advisor

This thesis examines abiotic processes controlling the transformation and distribution of carbon compounds in seafloor hydrothermal systems hosted in ultramafic rock. In Chapters 2 and 3, I conduct laboratory experiments to assess the relative extents of carbonate formation and CO2 reduction during alteration of peridotite by CO2(aq)-rich fluids. Results from these experiments reveal that formation of carbonate minerals is favorable on laboratory timescales, even at high H2(aq) concentrations generated by serpentinization reactions. Although CO2(aq) attains rapid metastable equilibrium with formate, formation of thermodynamically stable CH4(aq) is kinetically limited on timescales relevant for active fluid circulation in the subseafloor. It has been proposed that CH4 and potentially longer-chain hydrocarbons may be sourced, instead, from fluid inclusions hosted in plutonic and mantle rocks. Chapter 4 analyzes CH4-rich fluid inclusions in olivine-rich basement rocks from the Von Damm hydrothermal field and the Zambales ophiolite to better understand the origin of abiotic hydrocarbons in ultramafic-influenced hydrothermal systems. Comparisons of hydrocarbon abundances and stable isotopic compositions in fluid inclusions and associated vent fluids suggest that fluid inclusions may provide a significant contribution of abiotic hydrocarbons to both submarine and continental serpentinization systems.