Abstract

The contact relationships of the fault-intrusion are described, in detail, from the type locality. Textural and mineralogical evidence indicates that the fine-grained marginal facies of the fault-intrusion is not a priori evidence for magmatic emplacement. The production of 'flinty crush-rock' from brecciated quartzites downfaulted within the Glencoe cauldron is described from the south-western inner contact, and is shown to be a result of gas attrition. 'Flinty crush-rock' is recorded for the first time from the north-eastern contact with the country rocks outwith the cauldron, separated from the latter by a sheared microbreccia not found at the inner contact. The contact relations of the fault-intrusion with these 'flinty crush-rocks', more properly termed pseudotachylites, indicates that the fault-intrusion was emplaced as an entrained fluidized system of gas, solid phenocrysts and, probably, liquid droplets. The production of the sheared microbreccia at the outer contact is thought to be due to shearing stresses exerted by the entrained system on the heated wall-rocks.

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