A possible Al-Ti-augite high-pressure cumulate from the Glenelg inlier,NW Scotland

Aluminous clinopyroxenite is described from an exposure in the Eastern Lewisian metamorphic complex at Glenelg in NW Scotland. One specimen (S527) has exsolution lamellae of Ca-rich garnet in an omphacitic host, while another specimen (S526) contains Ca-Tschermakitic augite and green hercynitic spinel with reaction rims of garnet. Garnet exsolution is attributed to cooling to about 600°C at eclogite-stabilizing pressure, and is shown to depend on the Ca + Na content of the pyroxene. Pyroxene stoichiometry is questioned. Originally the pyroxenite was probably a high-pressure cumulate which crystallized and cooled within an eclogite-facies environment. Alternatively, it may have formed during an early phase of very high-grade metamorphism.