Deformational and metamorphic history of Moinian and Lewisian rocks between Strathconon and Glen Affric

Abstract

Seven distinct sets of fold structures have been recognised within 450 square kilometres of Moinian and Lewisian rocks. The earliest structures are only locally preserved, and are deformed by major folds which originally had approximately NE.-SW. axial traces and very variable axial directions. The formation of these folds was associated with high-grade Barrovian metamorphism and with the development of major slides. A pair of large N.-S. folds subsequently deformed this major fold pattern, apparently under conditions of fairly low metamorphic grade. High-grade metamorphism persisted or was re-established in part of the region during the formation of later structures oblique to the dominant regional trend. Subsequently a widespread set of folds whose style and orientation vary with varying metamorphic grade was superposed. In the area of higher grade these have approximately NE.-SW. axial traces, but their attitude in rocks of lower grade is more variable. Formation of another locally-developed set intervened between this widespread folding and the development of the last structures, which are mainly small NE.-SW. folds formed under low-grade conditions. Possible correlations with events in other parts of the Northern Highlands are discussed.