ABSTRACT
This chapter begins with description of the magmatic rocks because they were the first to form on the Earth. Sedimentary and magmatic rocks together are the raw material of metamorphic rocks. Magmatism is a series of processes including the melting of the mantle or crust and the solidification of magma as magmatic rock. The chapter examines processes of differentiation that modify the chemical composition of magma. It discusses theoretical conditions of a homogeneous and closed system, without the addition or loss of matter. The chapter explores the theory of plate tectonics, which is related to magma generation and magmatic composition. It determines two environments: the lithosphere, a combination of the crust and the outer part of the upper mantle, and the asthenosphere. The lithosphere can be likened to rigid plates that float like rafts on the asthenosphere and move as a result of convection currents, the force behind plate tectonics.
