High-P metamorphism and deformation of the Gurskebotn garnet peridotite, Sunnmøre, western Norway

In Gurskebotn relics of garnet-bearing peridotite occur enclosed in lower-grade ultramafic rocks. Mg-rich garnet pyroxenites and dikes of Fe-rich eclogite also occur within the ultramafic body. Garnet peridotite is extensively deformed and locally shows mylonitic textures. Garnets from ultramafic rocks always show
retrograde zoning. Some garnets from pyroxenites contain inclusions of chlorite, often concentrated in grain cores, suggesting derivation from a lower grade protolith. Eclogite garnets show slight prograde zoning. Two different generations of garnet occur in pyroxenites; they can be distinguished both
texturally and chemically. In garnet peridotite two generations of spinel-bearing kelyphitic rims on garnet can be observed. The earlier is usually deformed and has undergone some recrystallization. P,T-estimates suggest that ultramafic and mafic rocks have been metamorphosed under similar conditions. The most
reliable estimates indicate a metamorphic maximum at T?750°C, P?20 kb. However, the ultramafic rocks may have undergone more than one high-P metamorphic event, as indicated by the presence of two generations of garnet and kelyphite. The present data may be interpreted in terms of a model involving low-P protoliths for both ultramafic and mafic rocks.