Metamorphic Reactions And Metamorphic Facies

This book presents the genetic connections of metamorphism and geodynamics. It discusses the tectonic and magmatic processes as the reason of metamorphism, and the geological types of metamorphism, which define the features of Р-Т parameters and Р-Т-t paths. Three categories of metamorphism are distinguished depending on the heat flow rate: 1) at a geothermal gradient near to an average terrestrial ("normal") value; 2) at a heightened thermal gradient as the result of additional heat supply in the earth's crust by magmatic intrusions and diapirism of magma; 3) at a reduced thermal gradient during the collision of lithosphere plates and blocks of the earth's crust. The quantitative methods of description of metamorphism have been widely used in this book. The mathematical models of metamorphism have been studied in connection with magmatic intrusions, rifting process and magmatic diapirism. Mineral changes in the rocks controlled by variations of Р-Т of parameters, mass transfer and chemical reactions have also been characterized. The book proposes a quasi-stationary model of diffusion metasomatism with respect to the formation of zonal structures of minerals. The method of mineral thermobarometry for the conditions of unsteady equilibrium has been worked out; the quantitative analysis of mass transfer during metamorphic reactions in the rock matrix has been carried out, and the mobility of chemical elements at metamorphism has been estimated as well. The book is intended for specialists in the fields of petrology, mineralogy and geochemistry, and for students at the senior and graduate level.

The first edition of this book was published in 1965 and its French translation in 1966. The revised second edition followed in 1967 and its Russian translation became available in 1969. Since then, many new petrographic observations and experimental data elucidat ing reactions in metamorphic rocks have made a new approach in the study of metamorphic transformation desirable and possible. It is felt that this new approach, attempted in this book, leads to a better unders tanding of rock metamorphism. The concept of metamorphic facies and subfacies considers asso ciations of mineral assemblages from diverse bulk compositions as characteristic of a certain pressure-temperature range. As new petrographic observations accumulated, it became increasingly difficult to accommodate this information within a manageable framework of metamorphic facies and subfacies. Instead, it turned out that mineral assemblages due to reactions in common rocks of a particular composi tion provide suitable indicators of metamorphic conditions. Metamorphic zones, defined on the basis of mineral reactions, very effectively display the evolution of metamorphic rocks. Thus the im portance ofreactions in metamorphic rocks is emphasized. Experimen tal calibration of mineral reactions makes it possible to distinguish reac tions which are of petrogenetic significance from those which are not. This distinction provides guidance in petrographic investigations un dertaken with the object of deducing the physical conditions of metamorphism.

Metamorphic rocks are one of the three classes of rocks. Seen on a global scale they constitute the dominant material of the Earth. The understanding of the petrogenesis and significance of metamorphic of geological education. rocks is, therefore, a fundamental topic There are, of course, many different possible ways to lecture on this theme. This book addresses rock metamorphism from a relatively pragmatic view point. It has been written for the senior undergrad uate or graduate student who needs practical knowledge of how to interpret various groups of minerals found in metamorphic rocks. The book is also of interest for the non-specialist and non-petrolo gist professional who is interested in learning more about the geolo gical messages that metamorphic mineral assemblages are sending, as well as pressure and temperature conditions of formation. The book is organized into two parts. The first part introduces the different types of metamorphism, defines some names, terms and graphs used to describe metamorphic rocks, and discusses principal aspects of metamorphic processes. Part I introduces the causes of metamorphism on various scales in time and space, and some principles of chemical reactions in rocks that accompany metamorphism, but without treating these principles in detail, and presenting the thermodynamic basis for quantitative analysis of reactions and their equilibria in metamorphism. Part I also presents concepts of metamorphic grade or intensity of metamorphism, such as the metamorphic-facies concept.

This book is for senior undergraduate or postgraduate students who want an insight into some modern approaches to metamorphic petrology. Its aims are to explain, in reasonably simple, informal terms, the processes underlying (i) metamorphic reactions and (ii) the production of micro structures in metamorphic rocks, these currently being the things that interest me most, geologically. The first aim requires discussion of equilibrium factors, reaction kinetics and reaction mechanisms, empha sising both the complexity of realistic reactions and the need to combine the chemical and microstructural approaches to them. The second aim requires discussion of deformation, recovery, recrystallisation and grain growth processes, with emphasis on experiments on silicate minerals. The book concludes with a general attempt to relate chemical and physical processes in metamorphism, although it will be clear from reading earlier chapters (especially Chapter 4) that the two aspects can rarely be separated completely in detailed metamorphic studies. Petrological and experimental investigations of metamorphic reactions and microstructural development are advancing so rapidly these days that students are faced with an ever-increasing volume of information and a relatively rapid obsolescence of data. So, in this book I do not try to be comprehensive, or to present much so-called 'factual' information. Instead, I deal more with basic principles, in the hope that these will guide the student in his or her encounters with the details of specific metamorphic problems.

The first edition of this book was published in 1965 and its French translation in 1966. The revised second edition followed in 1967 and its Russian translation became available in 1969. Since then, many new petrographic observations and experimental data elucidat ing reactions in metamorphic rocks have made a new approach in the study of metamorphic transformation desirable and possible. It is felt that this new approach, attempted in this book, leads to a better unders tanding of rock metamorphism. The concept of metamorphic facies and subfacies considers asso ciations of mineral assemblages from diverse bulk compositions as characteristic of a certain pressure-temperature range. As new petrographic observations accumulated, it became increasingly difficult to accommodate this information within a manageable framework of metamorphic facies and subfacies. Instead, it turned out that mineral assemblages due to reactions in common rocks of a particular composi tion provide suitable indicators of metamorphic conditions. Metamorphic zones, defined on the basis of mineral reactions, very effectively display the evolution of metamorphic rocks. Thus the im portance ofreactions in metamorphic rocks is emphasized. Experimen tal calibration of mineral reactions makes it possible to distinguish reac tions which are of petrogenetic significance from those which are not. This distinction provides guidance in petrographic investigations un dertaken with the object of deducing the physical conditions of metamorphism."