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Structural setting and U–Pb zircon geochronology of the Glen Scaddle Metagabbro: evidence for polyphase Scandian ductile deformation in the Caledonides of northern Scotland

R. A. STRACHAN^*,* and J. A. EVANS

^* School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth PO1 3QL, UK
NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK

^* Author for correspondence: rob.strachan{at}port.ac.uk

Within the Scottish Caledonides, the Glen Scaddle Metagabbro was intruded into the Moine Supergroup of the Northern Highland Terrane after Grampian D₂ folding and prior to regional D₃ and D₄ upright folding and amphibolitefacies metamorphism. A U–Pb zircon age of 426 ± 3 Ma obtained from the metagabbro is interpreted to date emplacement. D₃–D₄ folding is constrained to have occurred during the Scandian orogenic event. In contrast, polyphase folding and regional metamorphism of the Dalradian Supergroup southeast of the Great Glen Fault is entirely Grampian. These differences are consistent with published tectonic models that invoke a minimum of 700 km of post-Scandian sinistral displacements across the Great Glen Fault to juxtapose the Grampian and Northern Highland terranes.

Key Words: U-Pb zircon • Caledonides • Scandian • Scotland