The effects of solid and vapour phase compositional variations on the amphibolite facies to granulite facies transition in the Agto metadolerites

Abstract

Metadolerites occurring in the vicinity of Agto (within the Isortoq Complex of central West Greenland) have been metamorphosed in upper amphibolite to garnet granulite facies. Detailed sampling and petrographic study of these demonstrates that the entire sequence of assemblages may occur in individual dykes, with the amphibolite assemblages normally restricted to dyke margins, garnet granulite facies rocks occurring in the dyke cores, and pyroxene granulite facies rocks intervening between these two. Bulk rock chemical analyses demonstrate that the dykes are chernically homogeneous with respect to all oxides except Al2O3 and Na2O. Nevertheless, variation in the latter two oxides is small, and demonstrably is not a parameter which significantly controls assemblage development.