Le facies granulite en norvege meridionale: I. Les associations minéralogiques

The basement of Southern Norway is a genetically homogeneous migmatite complex in which old supracrustals produced granitic and granodioritic ‘neosome’ during a late Precambrian (10⁹ years ago) regional metamorphism. Observed isograds of critical minerals: muscovite, cordierite, orthopyroxene indicate that the Telemark amphibolite facies in the North passes into the coastal Bamble granulite facies in the South. The data of expeimental petrology suggest that the transition, which took place at temperatures of 700–800°C, is essentially due to a decrease of the partial water pressure. P_H2O was equal to total pressure P_s in the amphibolite facies and lower than 2 kb in the granulite facies.