Picritic magma — residual dunite relationships in garnet peridotite at Kalskaret near Tafjord,South Norway

Field and textural relationships have indicated the tectonic emplacement of the Norwegian garnet peridotites as relatively cold intrusions into their present environment. Mineralogical data demonstrate considerable heterogeneity. Olivines and orthopyroxenes in garnet rich peridotites are significantly more ferriferous than those in garnet free peridotites. Mineralogical features indicate that the mineral assemblages have been equilibrated at subsolidus temperatures. However, the hypothesis that these garnet peridotites have resulted from the eclogite facies metamorphism in deep levels of the crust of other peridotite mineral facies assemblages is considered and rejected.Statistical analysis of the bulk rock composition data has substantiated the existence of a very strong linear composition trend, two end members being sufficient to account for almost the whole range of composition variation.The hypothesis favoured is that these peridotites have been involved in partial melting processes in the upper mantle. The Kalskaret garnet peridotite occurrence is considered to represent a case where the picritic partial melt fraction has not been completely liberated but has remained trapped and mixed with the dunitic residual fraction.