Book Review: RiMG v. 69
Reviews in Mineralogy and Geochemistry, Volume 69, Minerals, Inclusions, and Volcanic Processes edited by Keith Putirka and Frank Tepley III, The Mineralogical Society of America, Washington D.C., 2008, 674 pp. US $40 (ISBN 978-0939950-83-6).
Crystals in volcanic rocks provide valuable records of the history of a magmatic system prior to eruption. Phenocrysts and their inclusions record pre-eruptive conditions, the history of which may be lost when relying upon traditional whole rock analysis. Whereas geochemists were previously forced to deduce the pre-eruptive evolution of a magmatic system knowing only the end result, recent advances in microanalytical techniques reveal detailed information regarding magma storage, evolution, and eruption that was previously hidden from view. The thermodynamic conditions, dissolved volatile contents, and compositional evolution of a magma chamber is written in the crystals as they form; however, the interpretation of this information is complicated by the remarkable heterogeneity that has been observed at small scales (e.g. between zones in a crystal, or between melt inclusions trapped within a single crystal). The Reviews in Mineralogy and Geochemistry volume Minerals, Inclusions, and Volcanic Processes, edited by Keith Putirka and Frank Tepley III brings together a broad spectrum of researchers who are developing theoretical, experimental, analytical, and numerical techniques for extracting the information recorded in these crystals. This collection is more than simply a compilation of current research in the field; it provides detailed "how-to" information for those setting out in this rapidly growing field, where technique is absolutely critical to obtaining useful information. The wealth of knowledge presented in this volume and its corresponding supplementary materials will make it an indispensable resource for anyone working with, or interested in working with, the small-scale clues to magmatic conditions written in crystals and their inclusions.
The volume opens with an experimental view of magma crystallization kinetics by Julia Hammer. This chapter introduces the fundamentals of crystal nucleation and growth as revealed by dynamic experiments, in which pressure and temperature conditions are changed during the course of the run. This is followed by a series of chapters on thermobarometry applications in various systems. A chapter by Keith Putirka covers magmatic thermobarametry using liquid thermometers, crystal-melt thermobarometers, and crystal-crystal thermobarometers, employing primary rock-forming phases such as olivine, pyroxenes, and feldspars. J. Lawford Anderson et al. extend the application of thermobarometry to include minor and accessory phases found in granitic rocks, including zircon, rutile, titanite, and hornblende. Thor Hansteen and Andreas Kluegel discuss high-precision thermobaromtry of fluid inclusions, particularly useful for interpreting crystallization in shallow magmatic systems. A chapter by Jon Blundy and Kathy Cashman describes a variety of methods and approaches for extracting information regarding magmatic conditions from the end-product rocks, extending the discussion from thermobarometric techniques into assessment of crystallization during magma ascent, which leads very nicely into a discussion of magma ascent rates by Malcolm Rutherford in the following chapter. The discussion of magma ascent, crystallization, and degassing presented in these two chapters is particularly relevant to understanding the explosive nature of volcanoes, and is applied in both cases to Mt. St. Helens, among other recent significant volcanic events.
The study of melt inclusions trapped during crystallization of magmatic systems is handled over the next three chapters by Adam Kent, Gordon Moore, and the team of Nicole Métrich and Paul Wallace. The study of melt inclusions has enjoyed much attention in recent years, thanks to the development of new techniques for analyzing and interpreting the pre-eruptive compositional data they encode. In this volume, Adam Kent provides a thorough overview of melt inclusion selection, preparation, and analytical techniques, as well as some of the major pitfalls demanding vigilance on the part of the melt inclusion researcher. He concludes by discussing some features of compositional variation observed in basaltic melt inclusions. Gordon Moore gives an experimental and model-based assessment of volatile (H2O and CO2) solubility in melts, providing a basis for interpreting volatile contents and ratios in melt inclusions. Finally, Métrich and Wallace give a thorough overview of volatile analysis in melt inclusions, how volatile contents can be used to interpret degassing histories of basaltic systems, and the relationship between volatile compositions of melt inclusions and the relative explosivities of the eruptions that form them.
The next five chapters deal with compositional variation within and between crystals in igneous systems. Recent technological advances are currently enabling us to examine compositional variability in rocks and minerals on a spatial scale previously unattainable. In the chapter by Frank Ramos and Frank Tepley, the application of microsampling techniques including laser ablation, secondary ionization mass spectrometry, and micro-drilling followed by thermal ionization mass spectrometry are explored in detail, as well as their usefulness for assessing isotopic disequilibrium on the crystal-scale. Oxygen isotope variation among single crystals as well as within a single crystal is discussed by Ilya Bindeman, and uranium series disequilibrium among minerals is expertly evaluated by Kari Cooper and Mary Reid. Both isotope systems provide information on the timescales of magma genesis and residence time, and reveal the presence of xeno- and ante- crysts, in addition to true phenocrysts, in a variety of magma types. A detailed chapter by Fidel Costa, Ralf Dohmen, and Sumit Chakraborty also delves into the timing of magmatic processes, with step-by-step instructions for converting small-scale spatial variability in crystal composition into a timeline of compositional variation in magmatic systems using diffusion modeling. This chapter comes complete with an appendix explaining how to use finite difference methods for numerical modeling of diffusion processes.
The discussion turns to mineral textures in two chapters by Martin Streck and Pietro Armienti. As with many of the previously mentioned methods, quantitative textural analysis of crystalline volcanic rocks provides detailed, time-resolved information regarding pre-eruptive magma chamber conditions, but this information is not easily won. Technique, sample selection, and methods of interpretation are all critical to the outcome of textural analysis studies. The Streck chapter describes typical textures observed in common igneous minerals (plagioclase, pyroxene, olivine, amphibole, and accessory minerals) as they pertain to open-system behavior in magma chambers. Armienti discusses the intricacies of generating and interpreting crystal size distributions, including "unfolding" 3D crystal shapes from 2D images, with examples from Stromboli and Mt. Etna. The volume closes with a discussion of magma chamber dynamics as demonstrated by modeling compositional gradients in ignimbrites by Olivier Bachmann and George Bergantz.
The usefulness of this volume extends well beyond what is printed in its pages. In addition to the chapters themselves, extensive supplementary materials are available online at http://www.minsocam.org/MSA/RIM/Rim69.html. These materials include Powerpoint files of the presentations corresponding to each chapter (as they were given at the Mineralogical Society of America Short Course in December 2008) and several downloadable Excel spreadsheets to facilitate the application of the techniques described in the chapters. Also following from the Short Course and Reviews in Mineralogy and Geochemistry Volume is a compilation of teaching materials made available through the On the Cutting Edge program "Teaching Petrology in the 21st Century". These include the on-line tutorials "Teaching Phase Equilibria" and "Geochemical Instrumentation and Analysis", as well as a series of teaching activities on topics including Thermobarometry, Geochemistry of Fluid and Melt Inclusions, Kinetics of Mineral Growth and the Genesis of Mineral Textures, and the Physics of Mineral-Melt Segregation. The teaching materials are available online at http://serc.carleton.edu/NAGTWorkshops/petrology/index.html. Look for Minerals, Inclusions, and Volcanic Processes in the Table of Contents. This Reviews in Mineralogy and Geochemistry volume is exceptional in its timeliness and instructional resources, and is highly recommended for anyone interested in learning about, teaching, or launching a research program pertaining to the detailed magma chamber history that is written into a volcano's crystalline eruptive products.
Maureen D. Feineman
Department of Geosciences
Pennsylvania State University
University Park, Pennsylvania, USA