The effects of solid solution and diffusion on infiltration-driven metamorphism with application to metaperidotite, Val d’Efra, Central Swiss Alps

• Published in: Contributions to mineralogy and petrology 2012-07, Vol.164 (1), p.157-175
• Main Authors: Winslow, Nathan W., Ferry, John M.
• Format: Article
• Language: English
• Subjects: Dehydration; Earth and Environmental Science; Earth Sciences; Fluid flow; Geochemistry; Geology; Geophysics; Infiltration; Metamorphic rocks; Metamorphism; Mineral Resources; Mineralogy; Original Paper; Petrology; Rheology; Rocks; Spatial distribution; Upstream
• ISSN: 0010-7999; 1432-0967
• DOI: 10.1007/s00410-012-0731-y

The complication introduced by solid solutions in the analysis of infiltration-driven mineral reactions is that the mole fraction of tracer component i in fluid ( X i ) changes with reaction progress (ξ). The effect was incorporated into transport models for coupled fluid flow and mineral reaction by parameterizing the relation between X i and ξ. With specific reference to carbonation and hydration during regional metamorphism of the peridotite body in Val d’Efra, whose constituent minerals are all solid solutions, infiltration of a disequilibrium fluid produces a single sharp reaction front if rock is assumed uniform in composition. The reaction front separates completely unreacted rock downstream from rock upstream with ξ at a steady-state limit (ξ ss  ≤ ξ max ) that depends on input fluid composition (ξ max is the maximum possible value). Novel phenomena develop, however, if the flow medium, like the metaperidotite body, is composed of many small domains that differ in initial mineral modes and compositions but with X i homogenized at a spatial scale larger than the size of the domains (e.g., by diffusion). In this case, infiltration of a disequilibrium fluid produces up to as many different reaction fronts along the flow path as there are domains with 0 ≤ ξ