Fluid-Rock Reaction and Equilibrium

Reaction rates increase with temperature, and it has been hypothesized that equilibrium is approached in the hot reaction zones at midocean ridges (i.e. Bowers et al., 1988). If hydrothermal systems were simple, and thermodynamic data were complete and infallible, then one could predict equilibrium fluid composition with some accuracy from starting fluid and rock compositions and well-defined reaction pathways. This is a complex problem, and is under attack on a number of fronts by laboratories such as those of W.E. Seyfried Jr. at the University of Minnesota, Everett Shock at Washington University in St. Louis, and others. To date, the thermodynamic modeling and water/rock experimental approaches have produced important interpretations and predictions hydrothermal chemistry. The role of field and analytical chemical work done at PMEL and in other laboratories throughout the world is to determine what real hydrothermal fluids are like, and fit these data into new or existing models of hydrothermal systems. There is an interplay between field work, experimental work, and theoretical work among different laboratories that has made steady progress in understanding hydrothermal chemistry.