No abstract

Synopsis Detailed mapping SE of Fort Augustus has revealed the presence of two distinct successions, lithostratigraphically subdivided into nine formations. The upper Corrieyairack Succession is overlain conformably by the Leven Schists of the Dalradian Supergroup and is in tectonic contact with the lower Glenshirra Succession. Both successions are geochemically distinct from the Lower Dalradian and are considered to be part of the Grampian Division. The two successions are also petrographically and geochemically distinct from each other and these differences are considered to represent variations in the nature of the original sediments. The lower Glenshirra Succession appears to represent a series of arkosic sediments deposited in an oxidising environment whilst the Corrieyairack Succession has affinities closer to greywackes. There are also minor differences in geochemistry between the individual formations, which support the structural and stratigraphic interpretation of the area.

Synopsis Psammitic and semi-pelitic metasediments in the Corrieyairack and Loch Killin areas form part of the Grampian Division and underlie the Dalradian Leven Schist of Glen Roy. Two stratigraphic successions, the Corrieyairack and Glenshirra Successions, have been recognized which share a common structural and metamorphic history, although they are separated by a well-defined zone of high strain, here termed the Gair-beinn Slide. An early foliation (S 1 ) associated with the development of isoclinal F 1 folds and movement on the Gairbeinn Slide, is refolded by tight near-upright, NE-SW trending major F 2 folds, in particular the Corrieyairack Syncline. These structures are refolded by open F 3 folds with variably oriented axial traces.

Structures in Atholl nappe Grampian Division rocks in the Tayside Region can be traced NW into the supposedly older Central Highland Division in Speyside and Strath Nairn where they are the earliest fabrics present. Grampian Division/Central Highland Division contrasts appear to involve a gradational metamorphic change, and the existence of the Grampian slide supposed, by previous workers to separate the two units has not been confirmed. Atholl nappe fabrics have been shown to be coeval with those of Grampian orogenesis in the Tay nappe where their age is constrained by the 590 ± 2 Ma Ben Vuirich granite. Grampian orogenic structures can thus be traced, as the earliest structures present, as far as the Great Glen fault, a conclusion which may have a bearing on the significance of the fault as a terrane boundary. Central Highlands. The metamorphic rocks of the Scottish Central Highlands (Fig. 1) comprise units referred to the Southern Highland (youngest), Argyll, Appin and Grampian (oldest) groups. While Harris et al. 1978 regarded the Grampian Group as the oldest Dalradian group, it is broadly equivalent to the Grampian Division (Moine) (GD) of Piasecki (1980) who also identified the Central Highland Division (Moine) (CHD) which occupies several hundred square kilometres of Inverness-shire east and south of Inverness and which forms three other small inliers in Speyside, not distinguished on Fig. 1. Working largely in Speyside and adjacent areas, Piasecki & van Breemen (1983) regarded the CHD as lithostratigraphically broadly equivalent to Moine rocks of the N Highlands and

Synopsis The stratigraphic and structural interpretation of Grampian Group Dalradian rocks of the Monadhliath is greatly enhanced by integrating conventional mapping techniques with the results of a ground survey of total field magnetic intensity. Grampian age D 1 folds are delineated for the first time in this area.