Introduction to Metamorphic Textures and Microstructures

Technological advances over recent years, and examines interrelationships between deforma- a wealth of new research providing refreshing tion and metamorphism. It includes an exten- sive chapter on strain-related microstructures, new interpretations on many metamorphic microstructures, encouraged me to embark on and others on the controversial but important this considerably expanded and fully updated topics of porphyroblast-foliation relation- second edition. ships, and shear-sense indicators. The penulti- My aim in producing this book on metamor- mate chapter is on the topic of fluids and phic textures and microstructures has been to vemmg, and in the final, completely provide a detailed introduction to the thin- redesigned, chapter, the characteristic reaction section description and interpretation of meta- textures and microstructures associated with morphic rocks. Although primarily written for particular environments of metamorphism and specific P-T -t trajectories are discussed. the advanced undergraduate student, it should provide a useful first source of reference for This is done with reference to many of the any geologist dealing with metamorphic rocks. classic areas of metamorphism from around It is intended that the text should be both well- the world. Appendices giving mineral (and other) abbreviations (Appendix I), a glossary illustrated and comprehensive, but at the same of terms (Appendix II), and a list of key time concise and affordable. The book is comprised of three parts.

Table of Contents:
A Introduction to metamorphism and metamorphic rocks.- 1 Environments and processes of metamorphism.- 1.1 Environments of metamorphism.- 1.1.1 Regionally extensive metamorphism.- 1.1.2 Localised metamorphism.- 1.2 The limits of metamorphism.- 1.3 An introduction to chemical processes of metamorphism.- 1.3.1 Equilibrium assemblages and the phase rule.- 1.3.2 The energy of the system.- 1.3.3 Reaction types.- 1.3.4 Reaction rates.- 1.3.5 Diffusion.- 1.3.6 Fluid phase.- 1.4 Physical processes acting during metamorphism.- 1.4.1 Volume changes during reaction.- 1.4.2 Deformation processes on the macro-and microscale.- 1.4.3 Crystal defects and surface energy.- 1.5 Deformation-metamorphism interrelationships.- References.- 2 Facies concept and petrogenetic grids.- 2.1 Metamorphic facies, grade and zones.- 2.2 Petrogenetic grids.- References.- 3 Compositional groups of metamorphic rocks.- 3.1 Pelites.- 3.1.1 Medium-pressure 'Barrovian' metamorphism.- 3.1.2 Low-pressure assemblages.- 3.1.3 High-pressure assemblages.- 3.2 Metacarbonates and calc-silicate rocks.- 3.3 Quartzofeldspathic metasediments.- 3.4 Metabasites.- 3.5 Metamorphosed ultramafic rocks.- 3.6 Meta-granitoids.- References.- B Introduction to metamorphic textures and microstructures.- 4 Layering, banding and fabric development.- 4.1 Compositional layering.- 4.2 Introduction to stress, strain and fabric development.- 4.3 Classification of planar fabrics in metamorphic rocks.- 4.4 Processes involved in cleavage and schistosity development.- 4.5 Processes involved in formation of layering in gneisses and migmatites.- 4.5.1 The nature and origin of gneissose banding.- 4.5.2 The nature and origin of layered migmatites.- References.- 5 Crystal nucleation and growth.- 5.1 Nucleation.- 5.2 Growth of crystals.- 5.3 Size of crystals.- 5.4 Absolute growth times.- 5.5 Shape and form of crystals.- 5.6 Twinning.- 5.6.1 Introduction.- 5.6.2 Primary twins.- 5.6.3 Secondary twins.- 5.7 Zoning.- References.- 6 Mineral inclusions, intergrowths and coronas.- 6.1 Growth of porphyroblasts to enclose residual foreign phases.- 6.2 Exsolution textures.- 6.3 Inclusions representing incomplete replacement.- 6.4 Symplectites.- 6.5 Coronas (of high-grade rocks).- References.- 7 Replacement and overgrowth.- 7.1 Retrograde metamorphism.- 7.1.1 Environments of retrograde metamorphism.- 7.1.2 Textural features of retrogression.- 7.1.3 Specific types of retrogression and replacement.- 7.2 Overgrowth textures during prograde metamorphism.- References.- C Interrelationships between deformation and metamorphism.- 8 Deformed rocks and strain-related microstructures.- 8.1 Deformation mechanisms.- 8.2 Inter-and intracrystalline deformation processes and microstructures.- 8.2.1 Defects.- 8.2.2 Dislocations.- 8.2.3 Creep mechanisms.- 8.2.4 Grain boundaries.- 8.2.5 Recovery.- 8.2.6 Recrystallisation.- 8.2.7 Crystallographic-preferred orientations.- 8.3 Fault and shear zone rocks and their microstructures.- 8.3.1 Deformation of quartzitic and quartzofeldspathic rocks.- 8.3.2 Deformation of mafic rocks.- 8.3.3 Deformation of carbonate rocks.- 8.3.4 Distinguishing between schists and mylonites.- 8.4 The influence of deformation on metamorphic processes.- 8.5 The influence of metamorphism on deformation processes.- References.- 9 Porphyroblast-foliation relationships.- 9.1 Thin-section 'cut effects'.- 9.2 Porphyroblast growth in relation to foliation development.- 9.2.1 Recognition and interpretation of pre-foliation (pre-tectonic) crystals.- 9.2.2 Recognition of syntectonic crystals.- 9.2.3 Recognition and interpretation of post-tectonic crystals.- 9.2.4 Complex porphyroblast inclusion trails and multiple growth stages.- References.- 10 Shear-sense indicators.- 10.1 Introduction.- 10.2 Vein asymmetry and sense of fold overturning.- 10.3 S-C fabrics, shear bands and mica-fish.- 10.4 Differentiated crenulation cleavages.- 10.5 Spiralled inclusion trails.- 10.6 Mantled porphyroclasts and 'rolling structures'.- 10.7 Strain shadows.- 10.8 Grain-shape fabrics and crystallographic preferred orientations.- References.- 11 Veins and fluid inclusions.- 11.1 Controls on fluid migration and veining.- 11.2 Initial description and interpretation of veins.- 11.3 The 'crack-seal' mechanism of vein formation.- 11.4 Interpretation of fibrous veins.- 11.4.1 Syntaxial fibre veins.- 11.4.2 Antitaxial fibre veins.- 11.4.3 Composite fibre veins.- 11.4.4 'Stretched' (or 'ataxial') crystal fibre veins.- 11.5 Veins and melt segregations at high metamorphic grades.- 11.6 Fluid inclusions.- References.- 12 Deciphering polydeformed and polymetamorphosed rocks.- 12.1 Polymetamorphism.- 12.2 Local and regional complications.- 12.3 P-T-t paths.- 12.3.1 Introduction.- 12.3.2 Orogenic metamorphism.- 12.3.3 Orogenic metamorphism with a subsequent thermal overprint.- 12.3.4 Granulite facies P-T-t paths.- 12.3.5 Blueschist facies P-T-t paths.- 12.3.6 Eclogite facies P-T-t paths.- 12.4 Final comments.- References.- Appendix I: Abbreviations.- Mineral abbreviations.- Additional abbreviations.- Appendix II: Glossary.- Appendix III: Key mineral assemblages.- Zeolite facies.- Sub-greenschist facies.- Greenschist facies.- Epidote-amphibolite facies.- Amphibolite facies.- Granulite facies.- Eclogite facies.- Blueschist facies.- Albite-epidote hornfels facies.- Hornblende hornfels facies.- Pyroxene hornfels facies.- Sanidinite facies.- References for Appendices I-III and the plates.- Plates.