The Tectonics of the Schichallion Complex

Abstract

The results of the present investigation of the Schichallion complex can be summarized as follows :– (i) The succession established by Bailey & McCallien (1937) is confirmed. (ii) The imprints of four separate movements, F 1 to F 4 , have been found in the area. (iii) F 1 and F 2 are somewhat closely connected and are responsible for the two major systems of folding, which have produced the “Schichallion swing”. (iv) No indications of “twisting” or “torsion” have been found.

A Re-Interpretation of the Ben Lui Fold

“…These are respectively the Ardrishaig Anticline and the Loch Awe Syncline in the South-West Highlands (Roberts, 1963), (Text- fig, la), and the Sron na Iohlaire-Meall Uaine Anticline and the Sron Mhor-Coillebrochain Syncline (Sturt, 1961 ;Harris, 1963) in Central Perthshire (Text-fig, Ic). To the north-west, the primary structures face northwest, as recorded by Sturt (1961), Rast (1958), Harris (1963), Voll (1960), and Knill (1960), with axial planes fanning from the vertical to dip south-east, parallel to the basal Loch Skerrols Thrust and the Moine-Dalradian boundary slide, respectively. In both areas, the Cowal-Loch Tay flat belt and the steep belt to the north-west, in our opinion, define an original fold of the primary structures, developed during the primary deformation and subsequently modified by secondary deformation.…”

“…On this view, the primary structures in both limbs face south-east. Rast (1963) has noted the difficulty in reconciling such structures in the lower limb with the presence of north-west-facing primary structures in an analogous position in Central Perthshire, as described by Rast (1958), Sturt (1961), and Harris (1963) from the Schiehallion, Tummel, and Blair Atholl districts respectively.…”

“…In both areas, the Cowal-Loch Tay flat belt and the steep belt to the north-west, in our opinion, define an original fold of the primary structures, developed during the primary deformation and subsequently modified by secondary deformation. We have termed this fold a monoform (a fold of the primary banding (bedding and primary schistosities) in which one limb is flat-lying) in contrast to Bailey (1925), Bailey and McCallien (1937), Sturt (1961), and Rast (1958), who all considered the central steep belt to be the hinge of the primary and recumbent Ben Lui Fold. Harris (1963) has interpreted the central steep belt as part of such a monoform but considered that a primary syncline, equivalent to the Ben Lui Fold as defined by Bailey (1922), lies structurally below the Loch Tay Inversion.…”

Notes on the Structure of the Ben Lawers Synform

“…Folds with the relations shown by F 2 have not been described from adjacent areas, and are not equivalent to those called F 2 by Rast (1958), Sturt (1961), Jones (1964), and Ramsay (1963). The F 2 folds of Rast, Sturt, and Ramsay are all associated with a strong mineral lineation parallel to their axes.…”

Nick Rast and the recognition of the Avalonian Arc

“…Rast's contributions to British geology covered a wide range of topics, from field studies in Scotland, Ireland and Snowdonia describing structural (e.g., Rast, 1955, 1959;Rast, 1958aRast, , 1961aRast, , 1963, volcanic (e.g., Rast et al, 1958;Rast, 1961bRast, , 1969, stratigraphic (e.g., Smith and Rast, 1958;Harper and Rast, 1964;Rast and Litherman, 1970) and metamorphic (e.g., Rast, 1958b;Harris and Rast, 1960a) relationships, to process-oriented investigations of small-scale folding (e.g., King and Rast, 1956;Rast and Platt, 1957;Rast, 1964), boudinage (Rast, 1956), the growth of metamorphic minerals (e.g., Rast and Sturt, 1957;Harris and Rast, 1960b;Rast et al, 1962;Rast, 1965Rast, , 1966, and the ascent and emplacement of magmas (Rast, 1970). To each of these topics he brought an insight gained from both a keen observational eye and a perceptive ability to recognize the large-scale implications of his observations.…”