Pressure--Temperature--Time Paths of Regional Metamorphism II. Their Inference and Interpretation using Mineral Assemblages in Metamorphic Rocks

Abstract

A companion paper (England & Thompson, 1984a) investigates the pressure-temperature-time (PTt) paths followed by rocks undergoing burial metamorphism in continental thickening events. This paper discusses problems involved in inferring such paths from the petrological data available in metamorphic rocks and—once such paths are determined—how they may be interpreted in terms of the thermal budgets of metamorphism. Each of the principal facies series (glaucophane-jadeite, andalusite- sillimanite and kyanite-sillimanite) may be encountered by rocks involved in the thickening and erosion of continental crust in a regime of average continental heat flow. The inference of a minimum thermal budget required for a given metamorphism depends strongly on a knowledge of the PTt paths followed by rocks during the metamorphism. Discrimination between possible thermal regimes is greatly enhanced if portions of PTt paths, rather than single PT points, are available, and additional constraint is possible if these paths are supplemented by geochronological, structural and heat flow data.