FY 1989

Submarine venting of phase-separated hydrothermal fluids at Axial Volcano, Juan de Fuca Ridge

Massoth, G.J., D.A. Butterfield, J.E. Lupton, R.E. McDuff, M.D. Lilley, and I.R. Jonasson

Nature, 340(6236), 702–705 (1989)

Since the discovery of high-temperature venting on the East Pacific Rise in 1979, it has been expected, because of the physical properties of sea water at pressures and temperatures encountered during submarine hydrothermal circulation, that phase-separated fluids would discharge from ridgecrest vents. Although this notion is supported by the reported large deviations in vent-fluid chlorinity relative to that of sea water (-40% - +200%), by observations of venting at P-T conditions clearly within the two-phase region (220 bar and 420°C) and by fluid-inclusion data, unequivocal identification of phase-separated venting fluids has remained elusive. Here we report observations of chloride- and metal-depleted, gas-enriched fluids from a shallow vent field on the Juan de Fuca Ridge which confirm the expectation that phase-separated effluents are delivered to the deep ocean from some sea-floor venting systems.