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British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK (e-mail: e.phillips{at}bgs.ac.uk)
The Central Highlands of the Scottish Caledonides are dominated by a sequence of poly-deformed metasedimentary rocks largely belonging to the Grampian and Appin groups of the Dalradian Supergroup. In the northern part of the area these are separated from a suite of variably gneissose to locally migmatitic rocks by a number of prominent mid-crustal shear zones. The early evolution of the Central Highlands is interpreted in terms of regional (D1–D2) folding and N- to NW-directed thrusting accompanied by kyanite-grade metamorphism (P=7.0–8.0 kbar, T= 500–600°C). The later stages of this event were characterized by continued ductile shearing along the pre-existing shear zones under sillimanite-grade metamorphic conditions (P=4.7–5.9 kbar, T=585–695°C). The exact age of this progressive tectonothermal event remains uncertain, however, available geochronological data can be interpreted as indicating an entirely Precambrian age (c. 840–800 Ma). This questions previously held views of an entirely Caledonian age for deformation throughout the Highlands.
Key Words: Dalradian • Central Highlands Scotland • Caledonides • regional metamorphism • shear zones
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