Contact metamorphism in synkinematic two-mica granites produced by younger granitic intrusions, Galicia, N. W. Spain

Abstract

The thermal effects produced by relatively late granitoids on older synkinematic two-mica granites were studied. Both groups of granitoids are of late-Hercygian age and form part of the large Galician granite area in the N.W. of the Hesperian Massif. The thermometamorphic effects observed in the synkinematic two-mica granites consist of a complete recrystallization with progressive breakdown of biotite and muscovite and formation of andalusite, sillimanite, corundum, spinel, cordierite, quartz, plagioclase, K-feldspar and opaque minerals. Breakdown reactions of biotite and muscovite in the presence of quartz and under oxidizing conditions are proposed to explain the appearance of some of the newly formed minerals.