Pressure-volume-temperature relations for water at the depth of the magma chamber at 21??N on the East Pacific Rise suggest that the maximum sub-surface temperature of the geothermal fluid is about 420??C. Both the chemistry of the discharging fluid and thermal balance considerations indicate that the effective water/rock ratios in the geothermal system are between 7 and 16. Such low ratios preclude effective metal transport at temperatures below 350??C, but metal solubilization at 400??C and above is effective even at such low ratios. It is proposed that the 420??C fluid ascends essentially adiabatically and in the process expands, cools, and precipitates metal sulfides within the upper few hundred meters of the sea floor and on the sea floor itself. Copyright ?? 1980 AAAS.
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Geothermal system at 21??N, East Pacific Rise: Physical limits on geothermal fluid and role of adiabatic expansion