As for serpentinization of
Fo90 olivine, serpentinization of olivine with higher Fe contents produces
brucite proportionally more enriched in Fe relative to the
coexisting serpentine. A general feature of all model runs simulating
serpentinization of olivine is that the amount of magnetite present
in the equilibrium mineral assemblage is inversely correlated with
the Fe+2-content of serpentine and brucite. This is reflected by the
modeled H2(aq) concentrations, which are predicted to be maximal
at intermediate temperatures (Fig. 4) coinciding with the disappearance
of olivine from the equilibrium mineral assemblage and a
maximum predicted amount of magnetite present (Fig. 2). Concentrations
of H2(aq) decrease toward high temperatures, because olivine
is part of the equilibrium mineral assemblage and only small amounts
of magnetite and Fe-bearing serpentine are generated during alteration;
H2(aq) concentrations also decrease toward lower temperatures,
because ferrous iron is preferentially incorporated into brucite.