Chapter 10 - Equation-of-state of magmatic liquids

Abstract

Equation-of-State (EOS) of magmatic liquids includes their density, molar volume, partial molar volume of constituent oxides, thermal expansion, and compressibility (bulk modulus). In general, magma density and bulk modulus decrease and thermal expansivity increases the more felsic and, therefore, more polymerized the magmatic liquid. Other compositional variables affecting those magma properties include the Al/(Al+Si), how tetrahedrally coordinated Al3+ is charge-balanced, and the proportion of alkaline earths relative to alkali metals (MO/M2O). Solution of H2O and CO2 in the magma causes its density decrease. The of CO2 results in lowered magma bulk modulus, whereas H2O enhances it.