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Submitted by Gretchen Früh-Green, October 2015
A number of the Tethyan ophiolites in the Alps and northern Apennines are considered relicts of oceanic lithosphere and contain lower crustal and upper mantle sequences that are believed to have been exposed by detachment faults onto the seafloor. These ophiolite complexes often contain sections of carbonate-veined serpentinites and carbonate-serpentine breccias, so-called ophicalcites, which show similarities to the serpentinite-hosted carbonate deposits recovered at Lost City.
Our long-standing research targets the Jurassic Bracco-Levanto and Val Graveglia ophiolite complexes in Liguria (Italy), which provide spatial information (e.g., three-dimensional distributions and structures) and constraints on the preservation of geochemical fingerprints over time – information that is commonly unavailable in the modern marine system. An overall goal of our project is to obtain a better understanding of the sources of carbon and sulfur in these systems, how they are cycled from the basement to the fluids, the deposits and the biosphere, and how the carbon and sulfur budgets change with mineral-fluid and or microbe-fluid interactions over time. Another aim is to study the links among fluid-rock interaction, hydrothermal deposits and deformation processes and to compare these to modern marine systems along the Mid-Atlantic Ridge (PhD thesis M. Vogel, completed September 2015). We have been conducting petrological, major element, trace element and isotopic (O, C, S, Sr, B) analyses of basement rocks and the hydrothermal deposits to quantify fluid flow paths, mass transfer, and carbon cycles during progressive hydrothermal activity, with emphasis on processes leading to the formation of the ophicalcites. This comparative study will provide a better understanding of evolving, subsurface processes in serpentinite-hosted hydrothermal systems and will contribute to a comprehensive, integrated model of end-member hydrothermal systems in oceanic sequences formed at slow spreading ridge environments. Our work was supported by the Swiss National Science Foundation and ended September 2015.