Phase equilibria constraints on the chemistry of hot spring fluids at mid-ocean ridges
- Univ. of Minnesota, Minneapolis (United States)
Recent advances in experimental and theoretical geochemistry have made it possible to assess both homogeneous and heterogeneous equilibria involving a wide range of aqueous species at temperatures and pressures appropriate to model hydrothermal alteration processes at mid-ocean ridges. The authors have combined selected aspects of the chemistry of hot spring fluids with constraints imposed by a geologically reasonable assemblage of minerals in the system Na{sub 2}O-K{sub 2}O-CaO-MgO-FeO-Fe{sub 2}O{sub 3}-Al{sub 2}O{sub 3}-SiO{sub 2}-H{sub 2}O-HCl-H{sub 2}S to assess the effect of temperature on the composition of the aqueous phase and the activities of mineral components in plagioclase and epidote solid solutions. Assuming fO{sub 2(g)} and fS{sub 2(g)} controlled by pyrite-pyrrhotite-magnetite equilibria, a constant dissolved Ca concentration, and a dissolved Cl concentration equivalent to that of seawater, increasing temperature from 250 to 400C at 500 bars results in systematic changes in the composition of mineral phases, which in turn constrain pH and the distribution of aqueous species. The model predicts that dissolved concentrations of Fe, SiO{sub 2}, K, H{sub 2}S, and H{sub 2} increase, while Na and pH{sub (25C)} decrease with increasing temperature. That many hot springs vent fluids are characterized by variable degrees of conductive heat loss renders measured temperatures unreliable as indicators of the maximum temperature of subseafloor hydrothermal alteration processes. The implications of this are significant for hot spring fluids which reveal large Cl variations relative to seawater, since likely mechanisms to account for such variability typically require temperatures in excess of those inferred for subseafloor reaction zones by simply correcting measured temperatures for the effects of adiabatic cooling.
- OSTI ID:
- 5077690
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 55:12; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
BASALT
HYDROTHERMAL ALTERATION
MID-ATLANTIC RIDGE
HYDROTHERMAL SYSTEMS
PACIFIC OCEAN
THERMAL WATERS
CHEMICAL COMPOSITION
ROCK-FLUID INTERACTIONS
ANORTHITE
EPIDOTES
GEOCHEMISTRY
GEOTHERMOMETERS
GEOTHERMOMETRY
HOT SPRINGS
MAGNETITE
PH VALUE
PHASE STUDIES
PYRITE
PYRRHOTITE
SEAWATER
SOLID SOLUTIONS
TEMPERATURE EFFECTS
WATER CHEMISTRY
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
ALUMINIUM SILICATES
CALCIUM COMPOUNDS
CALCIUM SILICATES
CHALCOGENIDES
CHEMISTRY
DISPERSIONS
FELDSPARS
GEOTHERMAL SYSTEMS
HYDROGEN COMPOUNDS
IGNEOUS ROCKS
IRON COMPOUNDS
IRON ORES
IRON SILICATES
IRON SULFIDES
MEASURING INSTRUMENTS
MINERALS
MIXTURES
ORES
OXIDE MINERALS
OXYGEN COMPOUNDS
ROCKS
SEAS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SOLUTIONS
SULFIDE MINERALS
SULFIDES
SULFUR COMPOUNDS
SURFACE WATERS
THERMAL SPRINGS
THERMOMETERS
TRANSITION ELEMENT COMPOUNDS
VOLCANIC ROCKS
WATER
WATER SPRINGS
152003* - Geothermal Data & Theory- Rock-Water-Gas Interactions
580000 - Geosciences