Properties, Origin and Environment of Magmas

Abstract

Magmas are natural melts which are usually complex solutions of oxides or silicates. However, occasionally magmas composed of sulfides or metals may also occur. The complexity of the physicochemical behavior exhibited by these melts arises from the interactions of the solution components over a broad range of temperatures and pressures. A part of this complexity is revealed by the chemical analyses of rocks such as those presented in Table 4.1 and elsewhere, which frequently show 10 or more major components. However a large part of the behavior of melts is attributable to constituents which either do not regularly appear in the analyses or which appear as only traces in them. This is true for water and such other volatile constituents as HC1, HF, etc., the greater part of which may have been lost from the magma before solidification occurred. Then too the effect of a component is usually more closely related to its molar concentration than to its weight percentage so that light constituents such as H₂O and HF may have a proportionately larger effect (Buerger, 1948).