Open Session - SWISS GEOSCIENCE MEETINGs

102
Symposium 2: Mineralogy-Petrology-Geochemistry
2.2
Comparing carbon and sulfur isotopes in ophiolites and active peridotitehosted
hydrothermal systems
Schwarzenbach Esther M.*, Früh-Green Gretchen L.*, Bernasconi Stefano M.**
* Institut für Mineralogie und Petrographie, Clausiusstrasse 25, CH-8092 Zürich (esther.schwarzenbach@erdw.ethz.ch)
** Geologisches Institut, Universitätstrasse 16, CH-8092 Zürich
At slow and ultraslow mid-oceanic ridges extensional processes and crustal thinning lead to the exposure of ultramafic rocks
on the ocean floor resulting in serpentinization and precipitation of carbonate in open fractures. Serpentini-zation plays a
major role in the global marine bio-geochemical cycle and accounts for an important part of the exchange of sulfur and
carbon between seawater and the oceanic crust. The opaque mineral assemblage and the sulfur and carbon isotopic composition
strongly depend on fluid flux and redox conditions prevailing during serpentinization of the peridotites. Furthermore,
the unique conditions prevailing in these systems supports a microbial community with sulfate-reducing, sulfur-oxidizing
and methane-oxidizing bacteria leading to characteristic enrichments and depletions of the sulfur and carbon isotopes.
The Lost City Hydrothermal Field (LCHF) is as yet the only known example of an active, low temperature (T =