The Metamorphic Aureole of the Peridotite at the Lizard, Cornwall

Abstract

The peridotite in the Lizard area of Cornwall was intruded during a period of regional metamorphism of intensity producing blue-green hornblende amphibolites in rocks of basaltic composition. It is demonstrated that the peridotite has a high-temperature aureole in which assemblages characterized successively by brown-green hornblende, brown hornblende with hypersthene and augite, and typical hypersthene + augite pyroxene granulites are developed in rocks compositionally equivalent to the regional metamorphic assemblage. Chemical analyses of whole rocks, four hypersthenes, six clinopyroxenes, and five amphiboles are used to compare the metamorphic assemblages with those developed in other metamorphic gradients. In some areas of complex contact of peridotite and granulite or in granulite included within the peridotite, the granulite has become the more mobile rock and locally intrudes and includes blocks of the peridotite margin.