Hebridean Terrane

The Hebridean Terrane is one of the terranes that form part of the Caledonian orogenic belt in northwest Scotland. Its boundary with the neighbouring Northern Highland Terrane is formed by the Moine Thrust Belt. The basement is formed by Archaean and Paleoproterozoic gneisses of the Lewisian complex, unconformably overlain by the Neoproterozoic Torridonian sediments, which in turn are unconformably overlain by a sequence of Cambro–Ordovician sediments. It formed part of the Laurentian foreland during the Caledonian continental collision.

The Hebridean Terrane forms the westernmost strip of mainland Scotland, most of the Inner Hebrides and all of the Outer Hebrides. Similar rocks are also thought to be present on Shetland and have been proved west and north of the Outer Hebrides by BGS shallow boreholes and hydrocarbon exploration wells. The full extent of this terrane to the west is obscured by the effects of Mesozoic rifting.

The Lewisian complex consists of mainly granitic gneisses, subject to a series of metamorphic and tectonic events, interrupted by the intrusion of a major dyke swarm.

The protoliths for the Scourian complex were mainly granitic plutonic rocks intruded in the interval 3.0–2.7 Ga. They were metamorphosed to granulite facies and deformed towards the end of the Archaean. At the beginning of the Proterozoic, the Scourian gneisses were locally affected by deformation and retrogression to amphibolite facies in the Inverian event, which overlapped in time with the emplacement of the Scourie dykes.

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