function of temperature. Since serpentinization reactions are considered
to proceed fast at temperatures higher than ~100 °C in relation
to geologic times (Martin and Fyfe, 1970) all reactions are assumed
to reach (at least local) equilibrium. This assumption is an acceptable
approximation only if the reactions take place over a period of time,
which is less than the time scale of interest. Isothermal serpentinization
as a function of w/r was not computed for all 31 lithologies;
however, for comparison, two lithologies (olivine Fo90 and a
clinopyroxene-free harzburgite) were chosen to explore the influence
of w/r (initial w/r = 0.5, 1, and 10) on secondary mineralogy, fluid
composition, and redox conditions during serpentinization. The
models shown represent phase equilibrium calculations for coexisting
fluids and minerals at a specific temperature. They should
not be interpreted in terms of reaction progress. All calculations
presented here are performed for a pressure of 50 MPa, appropriate
to shallow to intermediate crustal depths. While the temperatures
of phase transitions in the models commonly increase with increasing
pressure, the relative thermodynamic properties of the phases involved
in serpentinization reactions are not particularly sensitive to
pressure. Consequently, moderate increases in pressure (up to a few
hundred MPa) results in an increase of only a few tens of degrees
for the reactions considered