Within the stipulations of the model, fluid produced by prograde reactions is expelled as convective flow is diverted around the resulting pressure maximum. Peak fluid-production rates are predicted to occur early in the metamorphic history. Such changes in flow regimes would be accompanied by changes in fluid source and, possibly, fluid composition, and would occur over small time intervals, years, relative to the total durations of most metamorphic events. Their results demonstrate that the principal effect of reaction progress on fracture permeability derives from precipitation and dissolution of quartz along fracture walls in the model system. Local equilibrium between fluid flowing through fractures and host rock is generally nearly attained at temperatures above approximately 200 C where permeabilities are on the order of to m and fracture spacing is less than approximately 100 m.
Local disequilibrium prevails in the vicinity of permeable thermal boundary layers.
These results lend credibility to many petrological studies of metamorphic fluid flow that assume local equilibrium. Multidimensional numerical models were also used to study fluid flow through metamorphosing rock on the meter and centimeter scales. Gerdes et al. The model can be used to simulate the formation of isotopic exchange fronts in two-dimensional flow systems. Detailed simulations of the effects of fluid flow on mineral parageneses have been carried out independent of hydrodynamic considerations.