Thermodynamic Modeling: a Unique Tool to Study Magma Evolution
Thermodynamic Modeling: A Unique Tool to Study Magmatic Systems
Nikitha Susan Saji
Given a set of variables - temperature, pressure and concentrations of chemical components forming the system – thermodynamic theory has the rigorous theoretical framework that can simulate chemical evolution of magmatic systems. This is what thermodynamic modeling does. Equilibrium phase composition of the system is calculated as a function of existing conditions. This article primarily explains the theory and method of thermodynamic modeling as applied to magmatic systems. The use of thermodynamic modeling in igneous petrology as an approach complimentary to the conventional geochemical modeling is also explored.
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Introduction
Magmas are the hot molten bodies produced by melting events within solid Earth. Most magmas exist as physically heterogeneous mixtures of melt, suspended crystals, and dissolved gases, with a bulk chemical composition so complex that it practically contains all the naturally occurring elements on Earth in one form or the other. These multiphase-multicomponent mobile melt systems have a primary rockforming role to play in geology. Buoyant ascent and subsequent solidification on cooling of these melt bodies is what creates the voluminous igneous rocks of Earth. Once formed by partial melting of the rocks in the source region, the magma undergoes a complex evolutionary process before it manifests itself on the surface as igneous rocks. The density contrast with the surrounding rocks makes the magma buoyant and it forces its way upward. Cooling and decompression accompanying this ascent cause crystallization as well as volatile exsolution from the magma. A host of processes such as crystal fractionation, liquid immiscibility, magma mixing and country rock assimilation - together referred to as magmatic differentiation processes – modify the primary magma compositionally leading its complex chemical and physical evolution to derivative magmas. The magma
Nikitha Susan Saji
Given a set of variables - temperature, pressure and concentrations of chemical components forming the system – thermodynamic theory has the rigorous theoretical framework that can simulate chemical evolution of magmatic systems. This is what thermodynamic modeling does. Equilibrium phase composition of the system is calculated as a function of existing conditions. This article primarily explains the theory and method of thermodynamic modeling as applied to magmatic systems. The use of thermodynamic modeling in igneous petrology as an approach complimentary to the conventional geochemical modeling is also explored.
1|Page
Introduction
Magmas are the hot molten bodies produced by melting events within solid Earth. Most magmas exist as physically heterogeneous mixtures of melt, suspended crystals, and dissolved gases, with a bulk chemical composition so complex that it practically contains all the naturally occurring elements on Earth in one form or the other. These multiphase-multicomponent mobile melt systems have a primary rockforming role to play in geology. Buoyant ascent and subsequent solidification on cooling of these melt bodies is what creates the voluminous igneous rocks of Earth. Once formed by partial melting of the rocks in the source region, the magma undergoes a complex evolutionary process before it manifests itself on the surface as igneous rocks. The density contrast with the surrounding rocks makes the magma buoyant and it forces its way upward. Cooling and decompression accompanying this ascent cause crystallization as well as volatile exsolution from the magma. A host of processes such as crystal fractionation, liquid immiscibility, magma mixing and country rock assimilation - together referred to as magmatic differentiation processes – modify the primary magma compositionally leading its complex chemical and physical evolution to derivative magmas. The magma
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