Implications of Pseudomorphic Replacement for Reaction-Transport Modeling in Rocks

Abstract

In reaction-transport models of petrological processes in rocks exhibiting replacement, reactions should be balanced on volume, and mineral reaction rate laws should contain a crucial dependence on stress. Existing models neglect this (e.g., Steefel and Lasaga, 1992); they ought to be improved to take account of authigenic textures. Widespread pseudomorphic replacement in rocks of all types follows from the facts that space in rocks is limited, that growth of new mineral grains would develop huge stress if adjacent grains did not simultaneously dissolve under the pressure developed by the growing grains, and that viscosity of rocks is probably enormous on the time scales of replacement reactions. Available experimental mineral rates of dissolution and growth miss the stressdependence of rates that operates in mineral reactions in rocks. This may underlie the apparent disagreement (Brantley, 1992) between laboratory rates and field-derived rates.