Book contents
- Frontmatter
- Contents
- Preface
- Acknowledgments
- List of units
- 1 Introduction
- 2 Physical properties of magma
- 3 Intrusion of magma
- 4 Forms of igneous bodies
- 5 Cooling of igneous bodies and other diffusion processes
- 6 Classification of igneous rocks
- 7 Introduction to thermodynamics
- 8 Free energy and phase equilibria
- 9 Thermodynamics of solutions
- 10 Phase equilibria in igneous systems
- 11 Effects of volatiles on melt equilibria
- 12 Crystal growth
- 13 Isotope geochemistry related to petrology
- 14 Magmatic processes
- 15 Igneous rock associations
- 16 Metamorphism and metamorphic facies
- 17 Deformation and textures of metamorphic rocks
- 18 Graphical analysis of metamorphic mineral assemblages
- 19 Geothermometry, geobarometry, and mineral reactions among solid solutions
- 20 Mineral reactions involving H2O and CO2
- 21 Material transport during metamorphism
- 22 Pressure–temperature–time paths and heat transfer during metamorphism
- 23 Origin of rocks
- Answers to selected numerical problems
- References
- Index
20 - Mineral reactions involving H2O and CO2
- Frontmatter
- Contents
- Preface
- Acknowledgments
- List of units
- 1 Introduction
- 2 Physical properties of magma
- 3 Intrusion of magma
- 4 Forms of igneous bodies
- 5 Cooling of igneous bodies and other diffusion processes
- 6 Classification of igneous rocks
- 7 Introduction to thermodynamics
- 8 Free energy and phase equilibria
- 9 Thermodynamics of solutions
- 10 Phase equilibria in igneous systems
- 11 Effects of volatiles on melt equilibria
- 12 Crystal growth
- 13 Isotope geochemistry related to petrology
- 14 Magmatic processes
- 15 Igneous rock associations
- 16 Metamorphism and metamorphic facies
- 17 Deformation and textures of metamorphic rocks
- 18 Graphical analysis of metamorphic mineral assemblages
- 19 Geothermometry, geobarometry, and mineral reactions among solid solutions
- 20 Mineral reactions involving H2O and CO2
- 21 Material transport during metamorphism
- 22 Pressure–temperature–time paths and heat transfer during metamorphism
- 23 Origin of rocks
- Answers to selected numerical problems
- References
- Index
Summary
INTRODUCTION
Most prograde metamorphic reactions involve dehydration or decarbonation. The large increase in entropy that accompanies the liberation of a volatile phase from a mineral ensures that rising metamorphic temperatures will favor reactions that produce a separate vapor phase. The properties of this phase are critical in determining which metamorphic reactions take place and under what conditions they occur. We have already seen in the simple example of the model metamorphic terrane treated in Chapter 18 that very different conclusions about the conditions of metamorphism can be reached depending on the assumptions made about the composition of the fluid phase (Fig. 18.4). The purpose of this chapter is to outline some of the important principles governing metamorphic reactions that involve a volatile phase.
The fluid phase in most metamorphic rocks is dominated by H2O and CO2. Both of these are initially derived almost entirely from the atmosphere (meteoric). Water is incorporated by minerals, such as the clays, during the weathering of rocks or the diagenesis of sediments. Carbon dioxide may also be similarly incorporated with the formation of calcite or dolomite. But the largest amount of CO2 enters metamorphic rock as calcite of biological origin formed from the shells of organisms. Both H2O and CO2 are trapped directly as pore fluid, but during compaction and diagenesis of sediment most of this is expelled. The fluid phase in metamorphic rocks is therefore derived largely from the breakdown of minerals rather than from the initially trapped pore fluid.
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- Principles of Igneous and Metamorphic Petrology , pp. 490 - 510Publisher: Cambridge University PressPrint publication year: 2009