The structure and structural dating of the Carn Chuinneag intrusion, Ross-shire

Abstract

Synopsis The Carn Chuinneag intrusion is a foliated granite pluton emplaced in the Moine rocks of the Northern Highlands of Scotland, containing large irregular inclusions of amphibolite. Minor sheet-like apophyses at the margin of the pluton extend into the Moine country rocks. The emplacement occurred after D 1 in static conditions and the Moinian envelope was distended. Structure contours suggest that the intrusion was originally a sheet-like pluton about 4 km (2.48 miles) thick. D 1 structures which are ubiquitous in the Moinian over a wide area surrounding the granite are entirely absent from the pluton. The widespread foliation of the pluton and sheet-like apophyses is equivalent to S 2 in the Moine rocks, and it is folded by major and minor scale D 3 folds closely similar in style to D 3 folds developed in the Moinian both inside and outside the granite aureole. D 4 deformed the whole of the pluton and its Moinian envelope. D 1 and D 2 structures of the Carn Chuinneag area and the Moine Thrust belt at Loch Eriboll are considered to be correlatives. Thus, pre-granite D 1 structures are inferred to be post-Arenig in age.

Proterozoic orogeny questioned: a view from Scottish Highland Field Workshops, 1995–1996.

“…It is the dominant tectonic fabric in the area, but it appears to have been depicted as D l in figure 4b of Shepherd (1973). It is consistent in style and orientation with that associated with the Sgurr Beag slide zone.…”

“…Rb-Sr whole-rock and bulk fraction zircon studies suggested an emplacement age of about 560 Ma, subsequently supported by four near-concordant U-Pb SHRIMP zircon ages in the range 540-620 Ma (Pidgeon and Compston 1992). Shepherd (1973) interpreted the intrusions as emplaced post-Dl, pre-D2 in the structural sequence, the inference being that Dl is Proterozoic. The dominant structure is D2 which consists of folds with a congruous L-S fabric that affects both the country rocks and intrusions, strongly rodding and foliating the latter.…”

“…The Dl structure consists of a bedding-parallel foliation in micaceous lithologies, designated Si' by Shepherd and correlated with a fabric by guest on May 11, 2018 http://sjg.lyellcollection.org/ Downloaded from described as axial planar to rare folds that he designated D l . There is also a grain-alignment lineation assigned to D l but this is described as coaxial with the dominant folds, D2 (Shepherd 1973 , fig 3). Two traverses were made to establish what structures and fabrics are cut by the Carn Chuinneag intrusion.…”

“…One was led by D. Wilson in Kildermorie Forest where the southern contact is exposed between [NH 464794] and [454784]. The other was in upper Strathcarron to examine a well exposed section in the Garbh Allt near Sallachy [490876] described by Shepherd (1973, fig. 9) where several granite apophyses cut the contact hornfelses.…”

The internal structure of the Moine Nappe Complex and the stratigraphy of the Morar Group in the Fannichs–Beinn Dearg area, NW Highlands

“…Three successive sets of tectonic structures occur within the Morar Group in the Achness Thrust Sheet (see also Shepherd 1973, Kelley & Powell 1985. S2 Ac is the dominant fabric, characterised by preferred orientation of biotite, muscovite and quartz ribbons.…”