The collective outgrowth of presentations at a September 1992 meeting titled The Transition from Basalt to Metabasalt: Environments, Processes, and Petrogenesis, held in Davis, California under the auspices of IGCP Project 294, to discuss recent advances and to identify important areas for further

Low-Grade Metamorphism explores processes and transformations in rocks during the early stages of metamorphic recrystallization. There has been little analysis and documentation of this widespread phenomenon, especially of the substantial and exciting advances that have taken place in the subject over the last decade. This book rectifies that shortfall, building on the foundations of Low-Temperature Metamorphism by Martin Frey (1987). The editors have invited contributions from an internationally acknowledged team of experts, who have aimed the book at advanced undergraduate and graduate students as well as researchers in the field. Contributions from internationally acknowledged experts. Documents the substantial and exciting advances that have taken place in the subject over the last decade.

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.

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 petrographie observations and experimental data elucidating reactions in metamorphie rocks have made a new approach in the study of metamor phic transformation desirable and possible. It is feIt that this new approach, attempted in this book, leads to a better understanding of rock metamorphism. The concept of metamorphie facies and subfacies considers asso cations of mineral assemblages from diverse bulk compositions as char acteristie of a certain pressure-temperature range. As new petrographie observations accumulated, it became increasingly difficult to accommo date 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 composition provide suita ble indieators of metamorphie conditions. Metamorphic zones, defined on the basis of mineral reactions, very effectively display the evolution of metamorphic rocks. Thus, the importance of reactions in metamor phic rocks is emphasized. Experimental calibration of mineral reactions makes it possible to distinguish reactions which are of petrogenetic sig nificance from those which are not. This distinction provides guidance in petrographie investigations undertaken with the object of deducing the physieal conditions of metamorphism. Within a metamorphie terrain, points indicating the same reaction constitute a line or a band, here designated by the term isoreaction-grad.