Fluid regime of granite formation in ultrametamorphic zones

A study of the P/T conditions of ultrametamorphic granitoids showed that in the transitional zone from amphibolite facies to granulite facies, the temperature of anatectic magmas rises from 680 to 800°C. This corresponds to a reduction in the activity of H₂O from 0.8-0.9 to 0.3-0.4. The results of gas chromatography also indicate a tendency towards a reduction in the ratio of H₂O/CO₂ during the transition from an amphibolite facies to a granulite facies. These data, along with the results of research into fluid inclusions, formed the basis for a model of an equal concentration of hydrogen in a fluid column, which describes the effects of ultrametamorphism in zonal metamorphic complexes. -P.Cooke