The structural evolution of the Dalradian of the Central Highlands of Scotland

Abstract

The first section of the paper is concerned with a detailed account of the structure of the classic Schiehallion area. The account is extended to the flat belt via the Glen Lyon-Ben Lawers area. It is demonstrated that major D1 folds involve the whole of the Appin and Argyll groups and now face SE. However, the original D1 folds were probably open upward-facing folds which have been refolded and modified by the dominant D2 deformation. D2 is represented by an antiformal complex which culminates downwards in the Boundary Slide, a zone of strong deformation associated with NW translation of Dalradian over the ‘young Moine’ rocks. D3 has been responsible for the rotation of the originally flat D2 structures into their present ‘steep’ attitudes N of Glen Lyon. D4 is represented by the strike-swing of the lower Dalradian formations, possibly related to early movements on the two major faults that bound the area. The concept of a D1 Tay Nappe which roots in the ‘young Moine’ to the N is retained, although the scale and flat attitude of that fold is regarded as in part a product of D2.

Reversals in the polarity of structural facing across an early ductile thrust; the Central Donegal Slide, northwest Ireland

“…The D, slide represented by the tectonic schist was probably never a single movement zone occupying the entire width of the schists. It is more plausible that the present tectonic schist unit represents the total spatial variation of numerous more discrete, localized planes of dislocation (see Treagus 1987).…”

A structural reinterpretation of the Tummel Belt and a transpressional model for evolution of the Tay Nappe in the Central Highlands of Scotland

“…2, section B-B′), here involved in two phases of post-D 2 folding. D 2 deformation in the Schiehallion area is deduced to be a combination of sub-vertical shortening in pure shear and top-to-the-southeast simple shear, the former more dominant at depth in the pile (Treagus, 1987). The rocks of the Tummel Belt will be shown to occupy a northwesterly extension of the originally flat-lying composite D 1 /D 2 Tay Nappe, a similar position to that occupied by the Schiehallion area.…”

“…In the southwest Highlands, where unaffected by D 2 , S 1 was produced under greenschist facies conditions; evidence, particularly from inclusions of S 1 in syn-D 2 porphyroblasts (Treagus, 1987), is that these conditions also prevailed in the Central Highlands during D1. The curvilinear hinges of D 1 folds and bedding (S 0 ) intersections with S 1 are related to major northeast-trending folds (see Fig.…”

“…Ph.D. thesis, Univ. Manchester, 1984;Treagus, 1987) along the northwest margin of the Flat Belt and the Aberfoyle Anticline, and the Ben Ledi Syncline and the Ben Vane Anticline (Mendum & Fettes, 1985) along the southeastern margin, possibly the equivalents of the folds to the northwest.…”

Chemical composition and K–Ar age of Phengite from Barrovian metapelites, Loch Leven, Scotland

“…4-5 kbar and ca. 300-500°C; Atherton, 1977) and have been deformed by three recumbent folds, the Appin Syncline, Kinlochleven Anticline and Ballachuish Syncline (highest), which all face towards the NW (Treagus, 1974(Treagus, , 1987Roberts, 1976;Roberts and Treagus, 1977;Hambrey et al, 1991). The lower limbs of the two synclines are occupied by the Fort William and Ballachulish Slides.…”