Our knowledge of metamorphic and deformational rock fabrics has been acquired largely by studying the products of deformation in ancient fold belts. As such, our understanding of how rock fabrics form has been built up from inferences about, rather than direct observations of, processes that might have operated, and many of those inferences have proved incorrect.

Metamorphism refers lo Ihe inineni logical and structural alteration of rock к in Karth's crust, and excludes alteration at or just beneath ihe surface, such as weathering and early diagencsis. However, diagenetic changes grade into mctamorphic changes in burial meuimorphism. In face* metamor-phism may occur in several geological environments, because assemblages react to changes in temperature (T), pressure (iJ) and activities of mobile chemical components, regardless ol the geological processes responsible for the changes. For example, identical or very similar assemblages can be formed by (1) deuleric alteration in an igneous intrusion 12) wall-rock alteration around a hydro! hernia) orebody. (3) low-tempe rat lire alteration around an igneous intrusion, (4) burial metamorphism of sedimentary/volcanic successions and (5) alteration, both local and regional, in geothermal areas (Vernon. 1976f.

This volume is devoted to the memory of the Russian petrologist D.S. Korzhinskiy. The world community of geoscientists has highly valued his contributions to petrology, particularly the discovery and thermodynamic description of open systems with perfectly mobile components. Korzhinskiy's work reached this community's attention because his book Physicochemical Basis of the Analysis of the Paragenesis of Minerals (1959, Consultants Bureau, New York) was translated into English. However, in the Soviet Union D.S. Korzhinskiy is also highly regarded for his contributions to geology and study of ore deposits as well as to theoretical petrology. Stratigraphy and geology of the Precambrian Aldan shield in Eastern Siberia; origin of lapis lazuli and phlogopite deposits and iron formations; boron mineralization; genesis of skarns and general theory of metasomatic zoning; origin of granites, charnockites and anorthosites; theory of the acid-basic interaction of components in the dry silicate melts: all of these were subjects of his more than 200 papers and books. The papers in the present volume span Korzhinskiy's broad interests. These papers were selected with the aim of illustrating the progress made in physicochemical petrology since Korzhinskiy.

Igneous petrology is the study of melts (magma) and the rocks that crystallize from such melts, encompassing an understanding of the processes involved in melting and subsequent rise, evolution, crystallization, and eruption or emplacement of the eventual rocks. Origin by crystallization from a melt seems a simple enough criterion for considering a rock to be igneous.

Petrology, from the Greek words petra , meaning rock, and logos, meaning knowledge, is the study of rocks and the conditions in which they form. It includes igneous, metamorphic, and sedimentary petrology.

Processes involved in the development of igneous and metamorphic rocks involve some combination of crystal growth, solution, movement and deformation, which is expressed as changes in texture (microstructure). Recent advances in the quantification of aspects of crystalline rock textures, such as crystal size, shape, orientation and position, have opened new avenues of research that extend and complement the more dominant chemical and isotopic studies.

Igneous and metamorphic petrology in the last decades of the twentieth century exploded into a broad, multifaceted, increasingly quantitative science. Advances in physical and field petrology and geochemistry have forever changed our thinking about the origin and evolution of magmas, their dynamic behavior, and the way in which they are intruded and explosively extruded. Developments in geochronology, quantitative evaluation of the role of heat and fluid transfer in crustal rocks, and new field discoveries have impacted our understanding of the evolution of metamorphic systems and their dynamic interaction with tectonic processes. Geophysics and mineral physics have provided new insights into the nature of the convecting mantle and its role as a giant heat engine driving magmatic and metamorphic processes. New tools of all kinds allow new ways of gathering petrologic data, while phenomenal developments in computers and computer software permit data to be stored, processed, and modeled in ways unimaginable as recently as a couple of decades ago.

This book is about metamorphic rocks: the processes involved in their formation and the reasons why they occur at particular places on the continents. It has been written to serve as an elementary text on the subjects of metamorphism and mountain building for non-specialist students of geology. It will be equally useful where geology is either the main or subsidiary subject and could be used by students intending to advance further in geology (the list of advanced texts in the further reading section would be more appropriate to such students). My intention in writing this book has been to try to dispel the notion that metamorphism comprises the 'haunted wing' of geology. Admittedly, there are rather a large number of technical terms in the book, but I hope that after working through it you will not find metamorphism an unduly difficult or obscure aspect of geology. Throughout, I have emphasised the strong links between mountain building, plate tectonics and metamorphic processes

The ever increasing amount of data on crystal arrangement in igneous and metamorphic rocks, alloys and ceramics, shows that the microtextures of these materials result from sequences of crystal growth and resorption. Metallurgists have become knowledgeable in the interpretation of textures and can make or modify textures of alloys in order to obtain specifjc responses to traction, distortion, etc. The modifications in texture can be reproduced or changed as often as desired. By analogy, it is probable that the microtextures observed in rocks may result from the same processes that govern similar textures in manufactured products. <...>

Metamorph;c processes have been taking place on a massive scale throughout the Earth's history, and have affected the bulk of the rocks now present in the crust. Despite this, they are not as well understood as sedimentary or volcanic processes, because metamorphism can scarcely ever be observed directly, and the study of metamorphic rocks is instead based on observation, inference and logic, founded in relatively simplistic experimental studies and the basic principles of chemistry and physics