Metamorphic isograds of Uwet area, southeastern Nigeria

Abstract

Progressive regional dynamothermal metamorphism of the kyanite-sillimanite type has been recognized in the Uwet area of the Oban massif in southeastern Nigeria. Metamorphic isograds, based on the entry of pelitic index minerals, biotite, garnet, kyanite and sillimanite have been mapped. The distribution of these isograds indicates a northwest to southeast increase in the intensity of metamorphism in the Uwet area from medium greenschist facies to uppermost amphibolite facies. The presence of kyanite and sillimanite indicate high pressure-high temperature Barrovian-type regional metamorphism whereas the absence of staurolite in these alumina-rich rocks is indicative of the high fugacity of oxygen during the metamorphism of the area. © 1985 Pergamon Press Ltd. All rights reserved.