Observations on eclogite- and granulite-facies rocks in the basement of the Caledonides

Summary Eclogite-facies metamorphism in the Glenelg inlier, NW Scotland, occurred after a phase of basic dyke intrusion (?Scourie dykes), and before a period of ?Caledonian mylonitisation. It possibly occurred during the Precambrian Morarian event since banded eclogitic rocks share the same ESE-dipping foliation as the overlying Moines. P-T conditions of metamorphism estimated as 750–600°C and 10–15 kb, suggest that the inlier is an upthrust segment of stable continental lower crust. Granulite-facies rocks of the NE Ox Mountains inlier, W Ireland, show evidence of Caledonian retrogression. Inferred P-T conditions (900–750°C, >10 kb) are those of a heated, lower crustal environment. The rocks are very similar to xenolithic material from the Scottish Midland Valley.