The Structural Geology of the Moine Thrust Zone in Coulin Forest, Wester Ross

Abstract

Summary In the Coulin Forest psammitic schists some 6000 feet thick, with infrequent politic horizons, overlie the Moine thrust : the rocks are the right way up and dip gently eastwards. The Moine outcrop has been divided into an eastern zone in which the rocks owe their structure and texture to regional metamorphism and a western zone in which the rocks exhibit the structural and metamorphic effects of the thrust movements. The structures in the western zone of the Moine and in the Torridonian and Lewisian below the Moine thrust are alike in style and orientation ; they are related to the thrust movements. The following movement history has been recognized in the rocks of the thrust zone :— 1. The formation of folds and linear structures trending E.-W. and generally plunging gently eastwards. The folds, which indicate some movement on N.-S. lines, are not consistently overturned in a single direction. These movements were accompanied by granulation, recrystallization and the formation of. orthorhombic fabrics. The relation of the E.-W. structures to the major transport along the thrusts is discussed. 2. The formation of folds and linear structures trending NNE.-SSW. and generally plunging to the north. These structures were produced by late shearing movements in zones of intense sliding. During this phase, the previously formed and folded mylonites were transported to the west-north-west.