Mid-Crustal Focused Fluid Movement: Thermal Consequences and Silica Transport

Petrologic evidence indicates that a fluid phase is almost invariably present during metamorphic activity. This association has led some petrologists to conclude that fluids are, at least sometimes, a source of metamorphic heat. An alternative view is that the association of fluids and metamorphic activity reflects the catalytic, rather than causal, role of fluids in metamorphism. This latter view is supported by numerical modelling of crustal metamorphism which suggests that regional-scale metamorphic fluid fluxes, estimated to be on the order of 10−8 to 10−10 kg m−2 s−1, are too small to significantly alter the thermal development of metamorphic systems (e.g. Peacock, 1987, 1989; Brady, 1989; Connolly and Thompson, 1989; Jamtveit, Bucher-Nurminen and Austrheim, 1990). Thus, it appears that anomalously large fluxes are required to generate notable thermal effects.