Trondhjemites, dacites and related rocks

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stage of much of the northern and western biostratigraphy is emphasized by the need to describe assemblages -- faunal and floral units of great utility for practical purpose in this rapidly developing pair of regions. The need to carefully describe species and genera for both biostratigraphic and taxonomic purposes is evident in many of the carefully prepared contributions. The Armstrong and Mamet paper is an exemplar of combined litho- and biofacies studies! The volume does emphasize the Paleozoic - 13 of the 17 papers deal with Paleozoic matters, An idea of the coverage is also provided in terms of the plates: trilobites, 3; conodonts, 20; ostracodes, 9; graptolites, 1; brachiopods, 10; palynomorphs, 4; the last item being the only ones for post-Paleozoic fossils, This volume is a must for students of Paleozoic invertebrates and biostratigraphy, and will also be of some interest to those dealing with the post-Paleozoic. The paper on the foraminiferal biostratigraphy of the interior Cretaceous will certainly be of concern to biostratigraphers elsewhere in North America. All-in-all, this is an outstanding contribution to North American biostratigraphy and invertebrate paleontology. A.J. Boucot, Corvallis, Ore.

PETROLOGY S.R. Nockolds, R.W.O'B. Knox and G.A. Chinner, 1978. Petrology for Students. Cambridge University Press, Cambridge, 435 pp., £ 6.50 (paperback), £ 17.50 (hardcover),

approximately half the text. The first section deals with igneous rocks and consists of twenty chapters. An essentially up-to-date petrographic text for elementary classes in petrology is given in Harker's fashion. Chemical analyses are now included with exact petrographic descriptions. Komatiites and alpine-type peridotites are briefly mentioned. Each chapter gives a list of references,' enabling the student to relate petrography to petrogeny. Textures of cumulate rocks should have been given more space. The treatment of pyroclastic rocks is not up to standard. In all, the igneous section is written in a comprehensive manner and contains essential information, with world-wide examples of typical rocks. The second section of the book consists of twelve chapters on sedimentary rocks. Here petrogenetic considerations are given in the text. Chemical analyses are omitted, but should be included in the next edition. Also here each chapter includes a list of references. The third section includes seven chapters and deals with the metamorphic rocks in a compact, but up-to-date descriptive and genetic manner. References include literature up to 1977f Drawings could be made more readable by indicating the different minerals, as is done in the igneous section. Typographical errors are scarce, the printing is good and the price is reasonable. The style and the comprehensive nature of the book makes it useful to students in geology and other earth sciences in both elementary and advanced courses. G. v.d. Kaaden, Meckesheim

As Harker's well-known Petrology for Students was not reprinted, a revised version

F. Barker (Editor), 1979. Trondhjemites, Dacites and Related Rocks. Developments

on the same lines has now been produced by Nockolds on igneous, by Knox on sedimentary, and by Chinner on metamorphic rocks. As in Harker's book, particular attention is given to carefully drafted drawings of thin sections. Besides a large number of new drawings, many of the original drawings are retained. The drawings are helpful in introducing the student into microscopical work. The biggest improvement on the original book is the treatment of sedimentary and metamorphic rocks, which now accounts for

in Petrology, 6. Elsevier, Amsterdam, 659 pp., Dfl. 135.00, U.S. $ 65.75. Teachers of petrology may feel a pang of disquiet when they read the title, thinking perhaps that when telling students that dacites are equivalent to granodiorites they may have been leading them astray. The name of the series might suggest that some new development has now revealed that trondhjemite is equivalent to dacite. They need have no qualms. In spite of the impli-

79 cations of the title (and even more the advertising which refers to 'trondhjemites, dacites, and the genetically related rocks') the evidence in this book does not support any such equivalence and indeed, the possibility receives little discussion. In the editor's opening chapter, the chemical definition of trondhjemite is given only in terms of some major element ranges (for which even the limits are not rigid) and there is no attempt to relate trondhjemites to dacites, nor any other group of rocks, by the comparative methods in common use. In later chapters, many of the rock analyses given as trondhjemite do not fall in the loose definition given at the outset. New data are given on the type trondhjemite (Chapter 17) but this does not clarify the definition (instead, an analysis of leuco-granodiorite f r o m the type area now fits the new chemical definition of trondhjemite). Why the description of type material was held over until Chapter 17 is unexplained (the order of chapters is certainly not based on eruption ages). There are many useful individual contributions, mostly reviews of existing knowledge, but why they have been collected together and grouped as they are is left to the reader to deduce. If your subject is tonalitic grey gneisses, basement metamorphism, or continental lithogenesis, then you may find interest in Chapters 6, 7, 8, 9, 10, 11, 12 and 13. Chapters 5 and 15 relate to ophiolites, whilst Chapters 13, 16, 18, 19 and 22 contain information on tonalitic intrusions, variously metamorphosed and of different ages and settings. Chapters 2, 20, 21 and 22 deal with Tertiary--Recent siliceous volcanics with emphasis on dacitic rocks. What connections can one make between these young volcanics and trondhjemites? In a comprehensive review of siliceous volcanics (pp. 13--121) by A. Ewart, trondhjemites are not mentioned, nor are they in the discussions of specific dacite volcanism in Chapters 20 and 21. Pre-Tertiary rocks are expressly omitted by Ewart because of difficulties of secondary alteration and ambiguity of tectonic regime (my italics). Trondhjemites are referred to in the chapter on Fiji (Chapter 22) but none of the analysed trondhjemites fits the definition given in Chapter 1! Most of the other chapters do not mention dacite (and one does

not mention dacite or trondhjemite) so one might be excused the suspicion that dacites belong in another book. A t 659 pages this one is t o o long, yet the problem of trondhjemite origin is still obscured by a plethora of hypotheses. If trondhjemite parent melts do form by so many diverse processes, then the possibility must be examined that post-eruptive processes have brought about the convergence in rock compositions. The nub of the trondhjemite problem is whether a crystalline igneous plutonic rock retains the composition of the parent liquid, and here alkali mobility is crucial. Alkali losses from tonalitic gneisses are affirmed in several chapters, which would accord with the modal white mica and normative corundum in trondhjemites. One equivalent of trondhjemite is quartz keratophyre, but this term appears only on a classification diagram (Chapter 22). Keratophyres are referred to in one or t w o places elsewhere, but the larger problem they entail, the spilites (and the intense soda metasomatism of the country rocks), is not mentioned at all. In the Preface, Bowen's doubt over the existence of trondhjemite magma is said to have been subsequently 'overcome by detailed field, petrographic, and chemical studies'. But this is to ignore the cause of Bowen's misgiving, which was that no fresh glass of albite granite composition had been reported up to 1928. A m o n g the literally thousands of analysed siliceous volcanics summarised or individually reported in this volume (Chapters 2, 20, 21 and 22) there is only one that falls in the trondhjemite range of Chapter l r Even this single specimen is odd in the context of its own suite, and with a reported loss on ignition of 1.85 wt. %, it must be doubted as a pristine liquid composition. Now, f i f t y years later and many thousands of analyses on, Bowen's doubt must surely have been overcome -- by total disbelief. Of graver concern are the objectives of the publishers, since there appear to be no editors guiding the series as a whole. If this book is showing a new trend in 'Developments in Petrology', then the publishers should change the title of the series. This latest volume largely reviews existing knowledge, with some new materiaJ added. Sire-

80

pie addition to existing information hardly constitutes much development of a subject, but if the additions are to be disparate and their collection into each volume not explained, the result is not development, merely accretion. D.K. Bailey, Reading H.S. Yoder Jr. (Editor), 1979. The Evolu. tion o f the Igneous Rocks: Fiftieth Anniversary Perspectives. Princeton University Press, Princeton, N.J., 588 pp., U.S. $ 44.00 (cloth), U.S. $ 15.00 (paper). This volume at once measures the progress of f i f t y years w o r k in igneous petrology while serving as eloquent testimony to the remarkable insight and foresight provided by Norman L. Bowen in his w o r k of the same title in 1928. The eighteen chapter headings originally used by Bowen are followed in this anniversary volume, with each chapter topic representing a separate contribution on the part of a scientist versed in the field. Many of the contributors are former collegues of Bowen or their students. Bowen's application of the principles of phase equilibria in close integration with field observations remains fundamental to petrology, but now much more field and experimental data (collected over a wider range of bulk compositions and at elevated pressures, with variable fluid components and oxygen fugacities) is available. The petrologist must consider not only equilibrium and fractional crystallizatior~, but also equilibrium and fractional fusion as factors in magma genesis and evolution. The scope and content of Bowen's original chapters are thus variously modified in this anniversary perspective; the editor, nevertheless, has achieved a commendable integration of the separate contributions in the overall presentation. Each chapter contains a review or synopsis of w o r k over the last f i f t y years and, where appropriate, an assessment of the change in viewpoint or interpretation of the topics relative to Bowen's opinion or conclusions of 1928. Each chapter contains a list of references and literature citations, therein some of which are rather extensive. Overall, this is an excellent volume which will be of interest to

those involved in the petrology or geochemistry of igneous rocks. The type size of this volume is welt chosen for easy readability and typescript errors in spelling and use of symbols and in the coding or citations to figures are minimal. A feature we do not like, however, is the small type size used for all figure captions and footnotes. The letter size used on some figures is also too small for the reduction used here. The only misgiving we have concerning this book does not relate to its actual content or style, but rather to a sense of what might have been. The progress of f i f t y years in the application of Bowen's philosophy has not only expanded and modified the role or scope of the topics in igneous petrology he considered, but has added significant new ones, such as the distributions of igneous rocks in space, time and tectonic setting, the characteristics of continental calc-alkaline rocks and other types w i t h o u t any necessary connection to basalts, the features of fusion in crustal rocks and development of migmatites, and the body of isotope and trace element data. This is evident in the many references to such topics (or their relevant field and experimental data) in the contributions to this volume. G.W. Putman and A. Miyashiro, Albany, N.Y. S.S. Augustithis, 1979. Atlas o f the Textural Patterns o f Basic and Ultrabasic Rocks and Their Genetic Significance. Walter de Gruyter, Berlin, 393 pp., DM. 255.00. S.S. Augustithis is well known already from t w o atlases published by Elsevier: Granites and Gneisses (1973), Basalts (1978). As in these t w o preceding books, the author clearly asserts himself as a supporter of metasomatism. It is thus very interesting to read the present book just after the recent magmatist publication: The Evolution o f Igneous Rocks (H.S. Yoder, Jr., Princeton University Press, 1979). The main items of such an inquiry are among the most attractive researches in modern petrology and geology because of the most important role of these rocks suggested by the plate-tectonics theory and its