Polymetamorphism in Movement Zones in the Caledonian Thrust Belt of Northwest Scotland
Microscopic examination of the textures and mineral orientations in the rocks within the Moine thrust belt is used in conjunction with the field evidence, which indicates several movement episodes of differing intensity and character, to elucidate the changing physical conditions in the northwest thrust front of the Caledonides. Many of the mylonites were formed in an early phase of the orogeny, in narrow (primary) "movement zones" in which the movements are concentrated. During a later phase, recrystallization and new mineral growth, under green schist or epidote-amphibolite facies conditions, occurred in the movement zones and outside them in places where secondary movement zones developed. Later phases show rather brittle, localized deformations, often following the earlier movement zones. Comparison is made of the movement zones and shear belts of the thrust belt with those found in other orogenic belts; and also with those found in nearby parts of the Caledonian belt. It is suggested that the primary...