Geochemistry of hydrothermal fluids from Axial Seamount Hydrothermal Emissions Study vent field, Juan de Fuca Ridge: Subseafloor boiling and subsequent fluid-rock interaction

Journal Article · Fri Aug 10 00:00:00 EDT 1990 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JB095iB08p12895· OSTI ID:5108427

Butterfield, D A; McDuff, R E; Lilley, M D ^[1]; Massoth, G J ^[2]; Lupton, J E ^[3]

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1. Univ. of Washington, Seattle (United States)
2. NOAA, Seattle, WA (United States)
3. Univ. of California, Santa Barbara (United States)

Hydrothermal fluids collected from the ASHES vent field in 1986, 1987, and 1988 exhibit a very wide range of chemical composition over a small area ({approximately} 60 m in diameter). Compositions range from a 300C, gas-enriched (285 mmol/kg CO{sub 2}), low-chlorinity ({approximately} 33% of seawater) fluid to a 328C, relatively gas-depleted (50 mmol/kg CO{sub 2}), high-chlorinity ({approximately} 116% of seawater) fluid. The entire range of measured compositions at ASHES is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust, followed by partial segregation of the vapor and brine phases. Other mechanisms proposed to produce chlorinity variations in hydrothermal fluids (precipitation/dissolution of a chloride-bearing mineral or crustal hydration) cannot produce the covariation of chlorinity and gas content observed at ASHES. There is good argument of the measured fluid compositions generated by a simple model of phase separation, in which gases are partitioned according to Henry's law and all salt remains in the liquid phase. Significant enrichments in silica, lithium and boron in the low-chlorinity fluids over levels predicted by the model are attributed to fluid-rock interaction in the upflow zone. Depletions in iron and calcium suggest that these elements have been removed by iron-sulfide and anhydrite precipitation at some time in the history of the low-chlorinity fluids. The distribution of low- and high-chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability. The relatively shallow depth of the seafloor (1,540 m) and the observed chemistry of ASHES fluids are consistent with phase separation in the sub-critical or near-critical region.

• OSTI ID: 5108427
• Journal Information: Journal of Geophysical Research; (United States), Vol. 95:B8; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
58 GEOSCIENCES
GEOTHERMAL FLUIDS
GEOCHEMISTRY
PACIFIC OCEAN
VOLCANIC REGIONS
ROCK-FLUID INTERACTIONS
BORON
BRINES
CALCIUM
CARBON DIOXIDE
CHEMICAL COMPOSITION
CHLORIDES
GASES
GEOLOGIC MODELS
HYDROTHERMAL SYSTEMS
IRON
LITHIUM
OCEANIC CRUST
PRECIPITATION
SALINITY
SEAWATER
SEPARATION PROCESSES
SILICA
ALKALI METALS
ALKALINE EARTH METALS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
CHLORINE COMPOUNDS
EARTH CRUST
ELEMENTS
ENERGY SYSTEMS
FLUIDS
GEOTHERMAL SYSTEMS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
METALS
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
SEAS
SEMIMETALS
SILICON COMPOUNDS
SILICON OXIDES
SURFACE WATERS
TRANSITION ELEMENTS
WATER
152001* - Geothermal Data & Theory- Properties of Aqueous Solutions
152003 - Geothermal Data & Theory- Rock-Water-Gas Interactions
580000 - Geosciences