Metamorphism in the George River Group Cape Breton Island, Nova Scotia

Abstract

<p> A sequence of metasedimentary rocks comprising the George River Group, Cape Breton Island, Nova Scotia, was studied. A petrographic examination of the five different rock types present -- marbles, amphibolites, paragneisses, skarn xenoliths, and granitic bodies was carried out. A petrochemical analysis, using X.R.F. methods was also completed.</p> <p> The GRG has undergone three distinct periods of metamorphism. The first was a period of kyanite grade regional metamorphism, believed related to the Grenville orogeny. High grade metamorphic minerals developed in the various lithologies present in the GRG. These minerals were kyanite, diopside, forsterite, hornblende, and muscovite.</p> <p> A chlorite grade regional metamorphism followed, creating such low grade minerals as chlorite, sericite, and serpentine. These minerals formed by the hydrolysis of higher grade metamorphic minerals.</p> <p> Following this low grade metamorphism, the GRG was subjected to a period of wollastonite grade contact metamorphism. This metamorphic period resulted from the injection of smaller granitic bodies believed related to the Acadian orogeny. The formation of contact metamorphic minerals such as, wollastonite, vesuvianite, phlogopite and sphene characterize the assemblages formed by this metamorphic event.</p> <p> The petrochemical analysis shows that these meta-sedimentary GRG rocks had protoliths of several types, including siliceous dolomitic limestones, siliceous limestones, greywackes, and basic volcanic sills. The amphibolites present crossing the GRG formed by the metamorphism of the basic volcanic sills.</p>