Material flux through the hydrothermal circulation at the mid-ocean ridge estimated by Ophiolite

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In order to estimate the depth of and material transfer through the hydrothermal circulation at the mid-oceanic ridge, sulfur contents and oxygen and sulfur isotopic ratios of a series of rock samples collected from the Samail Ophiolite in Oman were measured. Oxygen isotope ratios of the pillow lava unit indicates that this unit finally reacted with hydrothermal fluid whose temperature was less than 200℃ and at high water/rock ratio. In the sheeted dike complex, hydrothermal fluid whose temperature was higher than 350℃ was circulated into the boundary of the gabbro unit, if we assume that the water/rock ratio is unity in this unit. The altered gabbro might be reacted with hydrothermal fluid of 500℃ at very low water/rock ratio, 0.n. There are very good correlations between whole rock oxygen isotope ratios and whole rock strontium isotope ratios, and between whole rock oxygen isotope ratios and water content of rocks. It indicates that the oxygen isotope ratio is a very good indicator o … More f the degree of alteration. Sulfur content of the whole rock sample does not correlate with oxygen isotope ratio or strontium isotope ratio. In the pillow lave unit, sulfur content is very low because sulfur was extensively lost by hydrothermal circulation. In the sheeted dike complex unit, there are two parts : one has very low sulfur content because sulfur was lost by hydrothermal circulation and the other is enriched in sulfur compared to the original igneous sulfur content. Sulfur isotope ratio suggests that sulfur enrichment was caused by the precipitation of sulfide minerals from the hydrothermal fluid. In the gabbro unit, unaltered sample has sulfur content and sulfur isotope ratio similar to those of original igneous rock. It indicates that the sulfur loss did not occur at the bottom of the gabbro unit. If we estimate the total sulfur loss from the sheeted dike complex using the difference between average sulfur content of measured samples and original sulfur content of igneous rock, it exceed the amount of sulfur to produce the volcanogenic massive sulfide deposit which is now under mining on land. Less