New light on the Moine rocks of the Central Highlands of Scotland

Abstract

On the basis of new evidence, the Moine rocks SE of the Great Glen Fault are differentiated into two major units: the Central Highland Division, represented by a gneissose assemblage of about 1000 km 2 extent, and the Grampian Division, a younger and more extensive sequence of less deformed metasediments which is separated from the gneisses by a tectonic break, the Grampian Slide. Since the 2 Divisions have greatly differing tectonometamorphic histories, they are believed to correspond respectively to a basement complex and a cover sequence. The discovery of a suite of syntectonic Precambrian pegmatites ( c . 718 ± 19 Ma) equivalent in age to the Morarian pegmatites of Morar and Knoydart, permits the separation of Precambrian from Caledonian orogenic events. The Central Highland division is considered to be an eastward extension of the high-grade rocks which in part form the Glenfinnan Division W of the Great Glen Fault, widely held to be of Grenvillian age, whilst the Grampian Division is interpreted as early post-Grenvillian sediments affected first by a limited Morarian orogenic event, and subsequently by the Caledonian orogeny.

87 Sr/ 86 Sr chemostratigraphy of Neoproterozoic Dalradian limestones of Scotland and Ireland: constraints on depositional ages and time scales

“…1; Smith et al 1999) have been interpreted as basement upon which Grampian and Appin Group rocks were deposited unconformably (e.g. Piasecki & Van Breeman 1979;Piasecki 1980;Smith et al 1999). This interpretation is supported by evidence from regional mapping Smith et al 1999) and the absence of 800-900 Ma monazite ages in proven Grampian Group rocks .…”

Late Precambrian U–Pb titanite age for peak regional metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland

“…Only six grains dated in these studies have ages of ,1000 Ma. The top of the Moine sequence is not seen, and correlation with rocks south of the Great Glen Fault, such as the 'Central Highland Complex' (Piasecki 1980) or 'basement rocks' (Smith et al 1999) is not proven.…”

The pre‐Caledonian Inishkea Division of northwest Co. Mayo, Ireland: Its geochemistry and probable stratigraphic position

“…Although it remains possible that the Inishkea Division is Moine (and existing isotopic data have so far failed to reveal sufficiently old dates, which may not be interpreted as inherited, because of re-equilibration during subsequent metamorphism), it is more likely on the basis of existing evidence that the Inishkea Division sediments were deposited as a suite of greywackes in a restricted basin which formed between 1000 and 800 Ma ago. They were then first metamorphosed by an event which may be equivalent either with the 'Morarian' ages obtained from Scotland (Lambert 1969;van Breeman et al 1974van Breeman et al , 1978Piasecki 1980;Piasecki et ul. 1981), or represents a metamorphic event unique to Ireland.…”