The evolution of the Glencoe Cauldron

Abstract

Synopsis Previous views concerning the volcanic history and structural development of the Glencoe Cauldron (Roberts 1966a) are considered in the light of recent work by Taubeneck (1967) and Hardie (1968). The assumption that the andesite lavas were derived from outside the cauldron, has important implications concerning its evolution. An analysis of those Group 2 and Group 3 rocks associated with the first cycle of caldera formation shows that this caldera was lop-sided. Volcanic activity was concentrated along the northeastern margin, and the caldera formed by the flap-like subsidence of the caldera floor. Following the work of Hardie (1968), it is proposed that the steep contact between the volcanic and metamorphic rock in the northeast of the cauldron represents the wall to this caldera (cf. Clough et al. 1909). The eruptive products formed during this cycle of caldera formation, and the fault-intrusions which were emplaced during later cycles of caldera formation, indicate that the underlying magma chamber was layered. The volcanic activity resulting in caldera formation at the surface is related to the processes occurring within this chamber.