Inverse calculations reveal the three-dimensional geometry of time-integrated fluid flux over a 120 km2 area during peak Barrovian regional metamorphism in southeastern Vermont. Prograde changes in whole-rock CO2, 18O, and 13C and calculated fluid compositions at the peak of metamorphism were inverted assuming tracer mass balance to obtain the time-integrated fluid flux in three dimensions. Peak metamorphic fluid flow was spatially nonuniform with flux magnitudes ranging from ∼0 to 3·105 mol fluid/cm2 rock and flux directions ranging from vertical (upward and downward) to horizontal. Averaged over the entire study area, the magnitude of the time-integrated metamorphic fluid flux vector is ∼3.4·104 mol fluid/cm2 rock. The average flux vector trends 45° to the southwest and points upward at 36° from the present horizontal, parallel to formation boundaries on a regional scale. Fluids in the terrain carried ∼3·103 mol CO2/cm2 rock toward Earth's surface during the peak of metamorphism. Results suggest that local cross-layer transport processes are secondary to terrain-scale metamorphic fluid flow in driving prograde decarbonation reactions. Regional structure exerts a first-order control on the gross geometry of peak metamorphic fluid flow.

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