The ‘Central Highland Granulites’: cover-basement tectonics in the Moine

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Abstract
Summary: The Central Highland Granulites have been split into a cover assemblage of medium grade, little disturbed metasediments named the Grampian group, separated by a zone of sliding referred to as the Grampian Slide, from an underlying basement assemblage of high grade gneissose and migmatitic metasediments called the Central Highland Division. The Central Highland Division rocks are correlated on lithological, tectonic, metamorphic and radiometric grounds with the high grade Grenvillian rocks of the western Highland Moine, and are believed to represent their extension southeast of the Great Glen fault. The discovery of Precambrian ( c .720 Ma) pegmatites sheared by Caledonian (<570 Ma) sliding in the Central Highlands, enables the separation of Caledonian from Precambrian orogenic events in the rocks of both assemblages; their Precambrian orogenic history is so different, that the Central Highland Division rocks are considered to form a Grenvillian basement to the younger (Morarian) cover succession of the Grampian group. The western Highland Moine region is examined in the light of the tectonic cover-basement relationship postulated for the Central Highlands. The Loch Eil Division contains rock assemblages indistinguishable from the Central Highland Division, and others similar to the Grampian group. Evidence is put forward for a post Grenvillian, Morarian age for the Morar Division. The distribution of metamorphic zones in the Moine would seem to reflect the distribution of high grade basement and lower grade cover rocks, and may be in part determined by movements on a series of Caledonian slides, though this has not been demonstrated.