Migration of metamorphic fluid: some aspects of mass and heat transfer

Abstract

Minute amounts of free fluids contained along grain boundaries or in fluid inclusions in the rocks of the lower continental crust, mostly remain trapped until dislodged by thermally-induced hydrofracturing, deformation, or tectonic uplift. Volatile-components of minerals in the lower continental crust, are released at rates depending upon the changes in metamorphic heat-supply during tectonic processes, and at depths depending upon appropriate petrogenetic grids at near lithostatic pressure (Pfluid ∼ Prock). Pervasive flow of metamorphic fluid does not result in significant heat advection nor metasomatic mass-transfer. Layers of different permeability, strength and fertility (in the sense of amounts of metamorphic fluid released from minerals), control the local metamorphic hydrology. Only by focussing fluid-flow, by at least 103, can heat and mass advection become significant. The most favourable geological mechanisms to focus fluid-flow seem to be the reactivation of inherited heterogeneiities such as lithological contacts, old faults and shear zones, close to a deep-crustal aquitard or a fertile layer. © 1992.