Determination of time-integrated metamorphic fluid fluxes from the reaction progress of multivariant assemblages

An expression is derived for the calculation of time-integrated metamorphic fluid fluxes in two or more dimensions in rocks undergoing multivariant re actions under conditions of varying pressure, temperature and angle of flow . This calculation requires knowledge of mineral assemblages, modes and com positions, which are obtained from isobaric T-X-CO2 pseudosections construc ted using the program THERMOCALC and compared with those observed in east c entral Vermont. THERMOCALC is capable of reproducing peak mineral assemblag es, modes, compositions and the observed reaction sequences within the syst em KCaNaFMASCH for two kyanite grade pelitic carbonate rocks from a Barrovi an style regional metamorphic terrain in east central Vermont, U.S.A. Calcu lation of fluid fluxes for decarbonation reactions under conditions of hori zontal, layer-parallel flow produces time-integrated fluid flux figures of the order of 10(8) moles m(-2). Allowance for possible cross-layer flow fro m adjacent dehydrating pelites reduces this figure significantly, with epis odic cross-layer fluxes of the order of 10(5) moles m(-2) being capable of driving the observed decarbonation. Chlorite bearing carbonate protoliths w ould have initially dehydrated with increasing temperature, a process requi ring down-temperature fluid flow to produce the assemblages currently obser ved.