Advances in Physical Geochemistry - Böcker

The third volume in this series consists of eight chapters. The first three deal with kinetic aspects of compositional variations both within individual phases and across crystal boundaries. Basically, the authors use the kinetic theory and the sparsely available rate data to explain the formation of various types of zoning and the exsolution processes in silicates. Loomis rightly argues that "the kinetic inhibitions to reequilibration that preserve primary igneous crystals and high- grade metamorphic assemblages also affect the crystallization and prograde meta- morphism of these rocks." These "kinetic inhibitions" appear in the form of zoned crystals, reaction rims and disequilibrium assemblages. Their proper recognition and quantitative characterization leads to an understanding of the physico-chem- ical history of the rock. On a similar theme, I examine possible relationships between the exsolution processes in Ca-Fe-Mg pyroxenes and the cation order-disorder on nonequiva- lent crystallographic sites.A multi-technique study of exsolutions in crystals employing electron microscopy and X-ray structural refinements should contrib- ute greatly in understanding the thermal history of the rock. Many geothermometric studies result in discordant temperatures when the estimates are done using serveral coexisting pairs of minerals in a single specimen. Lasaga uses the kinetic rates of diffusion of various chemical species and explains the discordance through his "geospeedometric" approach.

The second volume of this series consists of three parts. Part I focuses on the research on intracrystalline reactions. This work, which began nearly two decades ago, is critically reviewed by Ghose and Ganguly in Chapter 1. Besides the review, the authors include some of their previously unpublished work to demonstrate how future research could aid in obtaining data on thermodynamics of solid solutions and in understanding the cooling history of igneous and metamorphic rocks. The latter is also the theme adopted by Kretz in the second chapter, which examines the redistribution of Fe and Mg in coexisting silicates during cooling. Chapter 3 contains new data on Fe-Mg distribution in clinopyroxenes. Dal Negro and his co-authors have selected a series of clinopyroxenes from volcanic rocks and present site occupancy data on several clinopyroxenes of intermediate compositions. The data set has not been published before and is the first of its kind. Part II of this book begins with a chapteron melts by Gaskell, who explores the relationship between density and structure of silicate melts. This is followed by the synthesis of data generated in the U.S.S.R. by Shmulovich and his co-authors on fluids. Blencoe, Merkel and Seil present a thorough analysis of the phase equilibrium data on feldspars coexisting with fluids in the third chapter in this part.

Today large numbers of geoscientists apply thermodynamic theory to solu­ tions of a variety of problems in earth and planetary sciences. For most problems in chemistry, the application of thermodynamics is direct and rewarding. Geoscientists, however, deal with complex inorganic and organic substances. The complexities in the nature of mineralogical substances arise due to their involved crystal structure and multicomponental character. As a result, thermochemical solutions of many geological-planetological problems should be attempted only with a clear understanding of the crystal-chemical and thermochemical character of each mineral. The subject of physical geochemistry deals with the elucidation and application of physico-chemical principles to geosciences. Thermodynamics of mineral phases and crystalline solutions form an integral part of it. Developments in mineralogic thermody­ namics in recent years have been very encouraging, but do not easily reach many geoscientists interested mainly in applications. This series is to provide geoscientists and planetary scientists with current information on the develop­ ments in thermodynamics of mineral systems, and also provide the active researcher in this rapidly developing field with a forum through which he can popularize the important conclusions of his work. In the first several volumes, we plan to publish original contributions (with an abundant supply of back­ ground material for the uninitiated reader) and thoughtful reviews from a number of researchers on mineralogic thermodynamics, on the application of thermochemistry to planetary phase equilibria (including meteorites), and on kinetics of geochemical reactions.

With the rapid development of fast processors, the power of a mini-super­ computer now exists in a lap-top box. Quite sophisticated techniques are be­ coming accessible to geoscientists, thus making disciplinary boundaries fade. Chemists and physicists are no longer shying away from computational mineral­ ogical and material science problems "too complicated to handle." Geoscientists are willing to delve into quantitative physico-chemical methods and open those "black boxes" they had shunned for several decades but with which had learned to live. I am proud to present yet another volume in this series which is designed to break the disciplinary boundaries and bring the geoscientists closer to their chemist and physicist colleagues in achieving a common goal. This volume is the result of an international collaboration among many physical geochemists (chemists, physicists, and geologists) aiming to understand the nature of material. The book has one common theme: namely, how to determine quantitatively through theory the physico-chemical parameters of the state of a solid or fluid.

Physical Chemistry of Magmas investigates the properties, structure, and phase relationships of silicate melts with invited contributions from an international team of experts. Data and some rules for estimating the properties and structures of melts, as well as the implications of the physical chemistry of silicate liquids to igneous petrology are presented. The second section then focuses on phase relationships, with particular attention on the application of experimental and theoretical petrology to modeling the origin of certain magmas.

Phase transitions in minerals are of interest to a wide spectrum of scientists - geolo- gists, mineralogists, solid state chemists, and physicists. We have now reached the point where mean field theory or Landau Theory of phase transitions as a function of temperature, pressure, or chemical composition can be usefully applied to natural materials, resulting in an improved understanding of the thermodynamics of signifi- cant constituents of the earth. Given the chemical complexity of so many silicate solid solutions, there are two distinct approaches to the problems posed by common minerals: one is to con- centrate on model compounds which could be synthetic analogs or natural end- members; the other is to work on typical minerals, with all the disorder and inhomogeneity that this implies. Model compounds provide the elements needed to build up a realistic understanding of the thermodynamic behavior of natural inor- ganic materials in all their complexity.In the first part of the book, a number of papers are devoted to structural phase transitions in quartz, Na-and Ca-feldspars, MgSi0 perovskite, and PbI , where Landau Theory and lattice and molecular 3 2 dynamics have been used to explain or predict thermodynamic behavior. A different thermodynamic approach has been used to understand phase separation and atomic ordering in solid solutions such as olivines, pyroxenes, rhombohedral carbonates and oxides. E. Salje (Chapter 1) applies the Landau Theory for the second-order phase transi- tion to the feldspar end-members albite, NaAlSi0 , and anorthite, CaAlSi0 .

The fifth volume in this series is focused on the chemical and physical interactions between rocks undergoing metamorphism and the fluids that they generate and that pass through them. The recognition that such pro­ cesses can profoundly affect the course of metamorphism has resulted in a number of recent papers and we consider that it is time for a review by some of the interested parties. We hope our selection of contributors provides an adequate cross section and demonstrates some of the flavor of this rapidly developing field. A cursory examination of the volume will reveal that there are widely divergent opinions on the compositions of metamorphic fluids and on the ways in which they interact physically and chemically with the rocks through which they pass. Since our own views are extensively discussed in Chapters 4 and 8, we leave the reader to determine his own brand of the "truth. " We wish to thank D. Bird, S. Bohlen, D. Carmichael, G. Flowers, C. Foster, C. Graham, E. Perry, J. Selverstone, R. Tracy, J. Valley, and R. Wollast for their chapter reviews. Thanks are also due C. Cheverton for her editorial assistance, and the helpful staff at Springer-Verlag New York.

The purpose of this volume is to present the latest planetary studies of an international body of scientists concerned with the physical and chemical aspects of terrestrial planets. In recent years planetary science has developed in leaps and bounds. This is a result of the application of a broad range of scientific disciplines, particularly physical and chemical, to an understanding of the information received from manned and unmanned space exploration. The first five chapters expound on many of the past and recent observations in an attempt to develop meaningful physical-chemical models of planetary formation and evolution. For any discussion of the chemical processes in the solar nebula, it is important to understand the boundary conditions of the physical variables. In Chapter 1, Saf­ ranov and Vitjazev have laid down explicitly all the physical constraints and the problems of time-dependence of nebular evolutionary processes. Planetary scientists and students will find in this chapter a collection of astrophysical parameters on the transfer of angular momentum, formation of the disk and the gas envelope, nebular turbulence, physical mixing of particles of various origins and growth of planetesimals. The authors conclude their work with important information on ev­ olution of terrestrial planets. Although symbols are defined in the text of the article, readers who are not familiar with the many symbols and abbreviations in astrophysical literature will find it useful to consult the Appendix for explanations.

The fourth volume in this series consists of eleven chapters. The first five deal with more theoretical aspects of the kinetics and mechanisms of meta­ morphic reactions, and the next six consider the interdependence of defor­ mation and metamorphism. All papers deal with natural processes that inter­ act on various time scales and with different degrees of mass and heat transfer. Consequently, many fundamental axioms of metamorphic petrol­ ogy and structural geology are questioned both for their accuracy and their usefulness. In raising such questions, most contributors have pointed to ways in which the answers could be forthcoming from appropriate experi­ mental studies or observations on natural materials. In their discussion of how order/disorder can influence mineral assem­ blages, Carpenter and Putnis emphasize that metastable crystal growth is common in metamorphic systems and state' 'there may be some reluctance (among many earth scientists) to accept that significant departures from equilibrium could occur." On the basis of presented evidence, they question whether reactions ever occur close to an equilibrium boundary. The neces­ sity for pressure or temperature overstepping is also required by nucleation­ rate theory. In any case, the degree of order is severely influenced by these kinetic effects in igneous, sedimentary, and metamorphic environments.