Metamorphic terrains II

Abstract

Most metamorphic rocks occur in fold mountain chains or in continental shields, which may be the eroded root zones of ancient mountain chains. Such metamorphic rocks therefore cover large areas of the continental crust (Fig. 4.1). They are termed regional metamorphic rocks and they include such types as schists and gneisses. Regional metamorphic rocks arise by the combined action of heat, burial pressure, differential stress, strain and fluids on pre-existing rocks (see p. 3 & pp. 20–25 for an explanation of these terms). The resulting rocks are always deformed and they exhibit such characteristics as folds and cleavages (Fig. 4.2). Large amounts of granite are often associated with regional metamorphic rocks, for reasons that will be explained later (p. 88).