A strain study of the Strathan Conglomerate, North Sutherland

Abstract

Synopsis The Strathan Conglomerate lies in the Lower Moinian of Sutherland and has been strongly deformed by two events, f 1 and f 2 . Minimum finite strain values X:Y:Z, calculated from deformed pebbles, range from 51:44.5:1 to 32:25:1 respectively. The size, shape and composition of the pebbles is compared to the nearby undeformed Watch Hill Conglomerate of Old Red Sandstone age. A simple method for estimating the minimum finite strain is outlined. The f 2 deformation has resulted in folding of the pre-existing flattened pebbles in some areas. During this folding and accompanying lower amphibolite grade metamorphism (M 2 ) quartz migration to low stress areas has occurred, resulting in a strong f 2 lineation and quartz rodding, both parallel to the X axis of the f 2 strain ellipsoid. On Ben Hutig a similar event has occurred; pre-f 2 planar quartz veins form a series of rods when folded by f 2 folds. The consequences of these results are discussed.