TRANSPORT OF STABLE ISOTOPES, KINETICS, DISPERSIVE ADVECTION, AND THE ISOTOPIC FRONTS OF BAUMGARTNER AND RUMBLE (1988)

Baumgartner and Rumble (1988) apply a 'kinetic continuum theory for stable isotope transport' to unidimensional infiltration of fluid into rock. Their numerical applications are restricted to the simplified case of rapid isotope exchange between phases, where the sharp isotope fronts of pure advection are distended by dispersive mechanisms only. However, kinetic limitations of isotope exchange are potentially an equally important distending mechanism, and it will only rarely be possible to ascribe front gradients to diffusion/dispersion alone. Abrupt isotopic changes at vein boundaries are more often a secondary signal of lithologic change than the expression of a retarded advective front. At such boundaries, diffusion and dispersion play a role that is comparable to, or greater than, that of advection, so that the detailed shapes of isotope fronts depend upon boundary conditions for the infiltration process. Zerodimensional box models have legitimate, if limited, uses in the modelling of fluid-rock interaction, and are reexamined. © 1990 Springer-Verlag.