marine hydrothermal systems; multidisciplinary studies; serpentinization; ophicalcites; volatiles; microbial activity; Lost City; Mid-Atlantic Ridge; carbonate precipitation; organic geochemistry; stable isotopes; carbon; sulfur; CO2 sequestration; hydrothermal systems; ophiolites
Schwarzenbach E.M., Früh-Green G.L., Bernasconi S.M., Alt J.C., Plas A. (2013), Serpentinization and carbon sequestration: A study of two ancient peridotite-hosted hydrothermal systems, in Chemical Geology
, 351, 115-133.
Boschi Chiara, Bonatti Enrico, Ligi Marco, Brunelli Daniele, Cipriani Anna, Dallai Luigi, D'Orazio Massimo, Frueh-Green Gretchen L., Tonarini Sonia, Barnes Jaime D., Bedini Rosa M. (2013), Serpentinization of mantle peridotites along an uplifted lithospheric section, Mid Atlantic Ridge at 11 degrees N, in LITHOS
, 178, 3-23.
Schwarzenbach E.M., Lang S.Q., Früh-Green G.L., Lilley M.D., Bernasconi S.M., Méhay S. (2013), Sources and cycling of carbon in continental, serpentinite-hosted alkaline springs in the Voltri Massif, Italy, in Lithos
, 177, 226-244.
Alt J.C. Schwarzenbach E.M., Früh-Green G.L. Shanks III W.C: Bernasconi S.M. et al. (2013), The role of serpentinites in cycling of carbon and sulfur: Seafloor serpentinization and subduction metamorphism, in Lithos
, 178, 40-54.
Schwarzenbach E.M. Früh-Green G.L. Bernasconi S.M. Alt J.C. et al. (2012), Sulfur geochemistry of peridotite-hosted hydrothermal systems: Comparing the Ligurian ophiolites with oceanic serpentinites, in Geochimica et Cosmochimica Acta
, 91, 283-305.
The alteration of mantle rocks during serpentinization is a fundamental process that has significant geophysical, geochemical and biological importance for the global marine system and for subduction zone processes, and has biogeochemical consequences during present-day weathering of variably altered mantle rocks on land. This proposal is a continuation of SNF project No. 20020-116226 (2007-2009) to complete the PhD project of Esther Schwarzenbach. This project is a comparative bio-geochemical and isotopic study of the Lost City hydrothermal system with modern and ancient serpentinite-carbonate systems. Lost City is unlike all other hydrothermal known to date and is characterized by metal- and CO2-poor, high pH fluids (9-11) with elevated hydrogen and methane contents resulting from serpentinization processes at depth. These alkaline, CO2-poor, CH4- and H2-rich hydrothermal fluids support sulfur-oxidizing, sulfate-reducing, and methane-cycling microorganisms living within the walls of the hydrothermal chimneys and in the subsurface. Ophiolite complexes exposed on the continents often comprise sections of carbonate veins, carbonate-serpentine breccias and serpentine-hosted deposits, so-called ophicalcites, which show remarkable similarities with the serpentinite-hosted carbonate deposits recovered at Lost City. This leads to the hypothesis that the Lost City vent field is a modern analogue for the hydrothermal processes that produced ancient ophicalcites. Modern serpentinization reactions can also be observed in the Jurassic ophiolites in Liguria (Italy). For example, fluids originating from deep aquifers circulate through the serpentinites of the Gruppo di Voltri and produce Mg-rich to Ca- or Na-rich, high pH (10 - 12) waters. As in the Lost City hydrothermal system, these springs have high hydrogen and methane contents, and the highest pH fluids are associated with carbonate precipitates. The proposed study specifically addresses a number of important open questions about the links between the inorganic reactions during serpentinization, biogeochemical cycling of carbon and sulfur, and microbial activity in these high pH systems. In this second phase of her thesis work, E. Schwarzenbach will investigate these high alkaline Ca-OH springs in Liguria and compare these with the completed studies of Jurassic ophicalcites in ophiolites and those drilled along the ocean-continent transition of the Iberian margin. She will perform geochemical, isotopic and organic geochemical analyses to characterize the volatile contents, C-O-H-S species, and sources and fluxes of volatiles and dissolved organic matter (DOC) in selected springs emanating from the serpentinites of the Gruppo di Voltri peridotites, north of Voltri and Sestri Ponente in Liguria. These studies will be carried out parallel to organic geochemical studies of S. Méhay (SNF Project 200021-1121840/1), and in collaboration with Prof. M. Lilley (Univ. Washington) and Dr. L. Marini (Univ. of Genoa). The overall goal of our studies is to quantify carbon and sulfur pools in active serpentinite-carbonate systems and to evaluate how these change with mineral-fluid and or microbe-fluid interactions over time. Specifically, we propose to:• Constrain the origin and cycling of carbon and sulfur in modern and ancient high pH hydrothermal systems. • Provide quantitative volume estimates of fluid and methane fluxes as well as the amount of CO2 and organic carbon that is sequestered in serpentinite-carbonate systems. • Provide a comparison of present-day and ancient serpentinite-carbonate systems in ophiolite terrains in Italy and the Iberian Margin.