Metamorphism in stable continental crust

Abstract

Most of the continental crust in the stable interiors of the continents consists of crystalline rocks with approximately granitic composition, partly or completely overlain by unmetamorphosed sedimentary rocks. The North American continent is a good example, with the crystalline basement exposed in the northern part, where it is known as the Canadian Shield, and in a number of inliers in the interior of the continent (Fig. 2.2). Study of the petrology, geological structure and geochemistry of âncient shields shows that the majority of rocks in them were formed by extensional and collisional plate movements, along with volcanic activity, during Proterozoic and later Archaean times (Windley 1984). It has been suggested that other tectonic mechanisms may have occurred in early Archaean times, and some of the evidence used to support this point of view comes from metamorphic rocks. This point will be discussed again later in this Chapter.