Pressures and temperatures of metamorphism in the eastern Dalradian

Abstract

Pressures and temperatures have been determined from locations in the eastern Dalradian using a number of different geothermometers and geobarometers. Temperatures range from 550°C in the low kyanite zone to about 800°C in the sillimanite–K feldspar zone. Pressures range from about 5.5 kbar in Glen Esk to 9–10 kbar in the Central Highlands. The barometric calibrations employed are consistent with the kyanite–sillimanite equilibrium. Evidence from mineral zoning suggests that rocks outside the Buchan area (in the Duchray Hill Gneiss, Glens Clova and Avon and in the Schichallion area) underwent a pressure decrease synchronous with the metamorphic peak. Regional temperature variations define a thermal high centred on the Cromar–Glen Muick–Duchray Hill Gneiss area. To the W of this high temperatures decrease rapidly. A sharp thermal break occurs between high grade sillimanite–K feldspar gneisses in Glen Muick and kyanite–staurolite schists to the W. This thermal contrast is attributed to a structural break which may be analogous to a number of other thermal features in the Dalradian.