Metamorphism of the Ben More-Am Binnein area, western Perthshire, Scotland

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Abstract
Several published studies suggest that a large part of the south-west Highlands, of which the area described forms a small part, represents an inverted stratigraphic succession (e.g. Bailey 1922 ; Shackleton 1958 ), and that the garnet isograd in the area is inverted ( Tilley 1925 ; Elles & Tilley 1930). The present study was undertaken in order to determine, as far as possible, the structural and crystallization history of these rocks. Three deformation phases have been recognized: the first resulted in the development of folds with north–south axes and axial planes lying statistically parallel to the regional foliation-surfaces; the second formed folds having axes with a 120° azimuth and axial planes dipping to the north-east; the third formed more open folds with Caledonoid (60°) axes. It is concluded that if large-scale regional inversion has occurred the rocks have possibly been overturned before the earliest distinguishable deformation phase. Microfabric study shows that recrystallization accompanied the three deformation phases. An intense and complex series of crystal growths, including growth of biotite, garnet, and albite, and regional diaphthoresis, occurred after development of the third-phase structures. This post-tectonic recrystallization formed the most common microfabric of the area, partly or totally obliterating earlier microfabrics; it is characterized by a low degree of preferred orientation of quartz c -axes. Detailed examination of the garnet isograd leads to the conclusion that there is no evidence of its inversion in this area.

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