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Inverse calculations reveal the three-dimensional geometry of time-integrated fluid flux over a 120 [km.sup.2] area during peak Barrovian regional metamorphism in southeastern Vermont. Prograde changes in whole-rock C[O.sub.2], [sup.18]O, and [sup.13]C 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*[10.sup.5] mol fluid/[cm.sup.2] 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*[10.sup.4] mol fluid/[cm.sup.2] rock. The average flux vector trends 45[degrees] to the southwest and points upward at 36[degrees] from the present horizontal, parallel to formation boundaries on a regional scale. Fluids in the terrain carried ~3*[10.sup.3] mol C[O.sup.2]/[cm.sup.2] 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. Keywords: metamorphism, fluid flow, inverse problem, C[O.sup.2], [[delta].sup.18]O, [[delta].sup.13]C.

A general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time-integrated fluid flux. The model is applied to regional metamorphism, quartz veins, and a metasomatized ductile fault zone.