Orogenesis magmas and metamorphism

Abstract

Tectonism, volcanism, plutonism and metamorphism are interdependent and contribute to the fabric of orogens and igneous rocks therein. Major lines of thought on problems relating to orogenesis in relation to igneous and metamorphic activity, generation of magma, rise of magma, and polymorphism and isostasy in crustal deformation, are outlined. The mechanics of emplacement of magma, at higher crustal levels, and the resultant fabric patterns are discussed at some length, as they are pertinent in interpretation of field data. The emplacement of granites and the major ideas in the generation of granite magma are discussed, and the new concepts of Buddington on the nature of emplacement of granite bodies, found at various crustal levels, presented. The tectonic implication of periodtites and serpentines, and the controversy over their mechanism of emplacement, are reviewed briefly. The concept of Hess that serpentinization below the Mohorovicic results in volume changes actuating mechanical movements such as uplifts, is suggested as applicable to the mechanics of uplift of sections of the stable Peninsular block of India.