A Morarian age for the ‘younger Moines’ of central and western Scotland
MUCH of our recent knowledge of the Moine metasediments1,2, which extend from the Moine Thrust across the Great Glen Fault to the boundary of the Dalradian Supergroup3,4 (Fig. 1), stems from the western Moine region. Here, late-Precambrian, Morarian ages (740–780 Myr) have been established from pegmatites in the Morar Division5, and a Grenvillian age (1,030 ±50 Myr) from the Granitic Gneiss of Ardgour in the Glenfinnan Division6. The ‘Central Highland Granulites’, generally regarded as ‘younger Moine’2,6, are little known geologically. Here we briefly outline the results of field (by M.A.J.P.) and radiometric investigations (by O.v.B.) in the Central Highland Granulites and the western Moines, which have fundamental implications for the evolution of these extensive metamorphic rocks, and for the nature of the Grenvillian–Caledonian interval in this sector of the North Atlantic Crust.
II.—The Moinian and Dalradian Rocks between Glen Roy and the Monadhliath Mountains, Inverness-shire
Synopsis The paper provides the first detailed geological description of a portion of the Grampian Highlands between Glen Roy in the west and the Monadhliath Mountains in the east. Moinian metasediments comprising thick granulites (Eilde Flags = Central Highland Psammitic Group) followed by a variable series of pelites and impersistent quartzites (Monadhliath Schists = Transition Group) are succeeded by Dalradian Limestone (Kinlochlaggan or Ballachulish Limestone = Basal Calcareous Group). The Monadhliath Schists are shown to be stratigraphically equivalent to those of Lochaber below the Ballachulish Limestone. Structurally the area consists of north-easterly anticlines and synclines which are generally isoclinal and often overturned. Many formational junctions are clearly stratigraphical, but the point is discussed whether tectonic contacts (slides) may also be present. Most of the metasediments are of garnet grade, but in the east there is a poorly-developed kyanite zone, and a well-developed sillimanite zone. The high-grade zones are related to a major migmatite and pegmatite belt (the Strathspey Complex); another pegmatite belt occurs farther west around Loch Laggan. Post-tectonic granite, quartz-diorite, diorite and appinite intrusions are also present. The district is traversed by several important north-easterly faults which are later than both the metasediments and the intrusions.
A Metamorphic Boundary in the Moine Schists of the Morar and Knoydart Districts of Inverness-shire
Abstract A re-examination of the Moine—Sub-Moine boundary of the Morar dome shows it to be a zone of transition between two metamorphic states. Some notes on the structure accompany a mineralogical description of the changes across the boundary; discussion is made of evidence that the metamorphic boundary transgresses the geological boundaries. The schists of the core are thought to be in a lower metamorphic state than those of the envelope.