Preface to the Third EditionThe 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 metamorphic 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 assocations of mineral assemblages from diverse bulk compositions as characteristie of a certain pressure-temperature range. As new petrographie 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 composition provide suitable 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 metamorphic rocks is emphasized. Experimental calibration of mineral reactions makes it possible to distinguish reactions which are of petrogenetic significance 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. Points along the isoreaction-grad represent metamorphie conditions (P, T, PvolatUes) corresponding to the pertinent reaction. As the term implies, an isoreaction-grad is defined by a specific re action and is therefore more significant than an isograd based on the appearance or disappearance of a mineral or mineral assemblage not related to a specific reaction.Thus, this presentation of the principles of rock metamorphism differs from that of previous editions: mineral reactions in several rock groups of common composition (mafic, ultramafic, pelitic, marly, and dolomitie) are treated in separate chapters. For each compositional vi Preface to the Third Edition group, the various mineral reactions that take place during the course of metamorphism are discussed. Large divisions of metamorphic grade, also defined on the basis of mineral reactions in common rocks, provide a convenient overview of metamorphic conditions. These divisions are designated as very-Iow-, low-, intermediate-, and high-grade metamorphism.The new concept is straightforward in its application. It has been used successfully in the field by the author's coworkers and others. It is hoped that this book will provide some guidance in the petrographie studies of metamorphic terrains: only rocks having certain compositions need be examined in great detail. Instead of extensive investigations, o...
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