Seawater-crustal reactions in submarine hydrothermal systems may exert an important influence on the mass and isotopic composition of sulfur in seawater, but such effects have been ignored due to a lack of data and understanding of sulfur in these systems. Subduction of altered oceanic crust has also been suggested to account for the 34S-enrichments of arc volcanics and to produce heterogeneities in the sulfur isotopic composition of the mantle, but little is known about the distribution or isotopic composition of sulfur in altered oceanic crust. It is proposed to analyze the sulfide mineralogy, sulfur contents, and sulfur isotopic composition of a section through the Troodos ophiolite in order to understand the geochemistry of sulfur during seawater-crustal reactions and to address these problems. The proposed results will provide a necessary test of recent results from seafloor samples. Moreover, the ophiolite section will provide essential new data on deep reaction/upflow zones, which are lacking from the oceanic sample suite. Such zones exert important controls on hydrothermal fluids which form massive sulfide deposits and vent onto the seafloor. The proposed study will also permit testing of theoretical models which predict zones of sulfur and 34S enriched rocks in the deep recharge areas of hydrothermal systems. Such rocks have not yet been observed from the seafloor.
