| Journal of Petrology | Pages |
© 1998 Oxford University Press |
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2nd edn, by Alan P. Dickin. Cambridge University Press, Cambridge, 1997. 490 pp. ISBN:0 521 43151 4. Paperback. £29.95 (US$44.95).
This is the very welcome second edition to the well-received book Radiogenic Isotope Geology by Alan Dickin. It is in paperback, and the author and the publishers are to be congratulated on producing this updated second edition just 2 years after the publication of the first edition. It is a testament to the success of the first edition, and the importance of radiogenic isotopes in almost every field of the Earth Sciences.
Radiogenic isotopes are used both as absolute chronometers and as geochemical tracers. The rapid development of mass spectrometric techniques and the explosion in the numbers of high-quality isotope determinations since the 1970s have been highly influential in the development of geology from a primarily descriptive subject to one with considerable emphasis on the understanding of natural processes. This has happened, first, because the study of natural processes requires a knowledge of the rates at which they occur, and that in turn depends on the precision with which events can be dated; and, second, because radiogenic isotopes provide highly sensitive chemical fingerprints of the materials caught up in different processes, and of their sources.
It has been argued that the widespread application of radiogenic isotopes was the catalyst for the redefinition of subject areas within geology, and certainly the extent to which isotope geology should be taught as a separate subject, or integrated throughout graduate and undergraduate courses, is a subject of continuing debate. Nowhere are such issues brought into greater focus than between the covers of a new textbook. Historically, geochronology was regarded as a subject in its own right, and as isotopes were more widely applied there was a natural progression into books on isotope geology. However, it also became clear that particularly in geochemistry there were many pitfalls to be encountered if isotope data were considered in isolation from field geology, geophysics and other major and trace element geochemical analyses. The result was books on igneous petrology, or sedimentary geochemistry, which compressed the systematics of stable and radiogenic isotopes into a chapter or two, and then sought to apply them to a range of different topics.
In this book, Alan Dickin makes the case that there are advantages in considering isotope geology as a subject in its own space available in a whole book on radiogenic isotopes, including two thorough chapters on nucleosynthesis and nuclear decay, and on experimental techniques. Some sense of the balance of subjects covered can be gleaned from the numbers of pages devoted to different topics: 160 pages to the uses of Sr, Nd and Pb isotopes in geochronology, crustal and mantle evolution, and igneous geochemistry; 60 pages to K-Ar, Ar-Ar and the rare gases; 55 pages to U-series dating and its application in igneous petrogenesis; 43 pages to Re-Os and specialist isotope schemes such as Lu-Hf and La-Ce; and 80 pages to cosmogenic nuclides, extinct radionuclides and fission track dating. As the title suggests, there is no space for stable isotopes, and many of the examples are broadly `hard rock', namely, mantle and crustal evolution and igneous petrogenesis. In compiling the second edition, the author has made minor corrections, and has provided a useful 36-page Appendix of updated material and references that highlight the main developments since the preparation of the first edition. This clearly speeded up the revision process, but with the inevitable consequence that the new material is not integrated within the main text.
Radiogenic Isotope Geology is most obviously in competition with Faure's Principles of Isotope Geology, which treats stable as well as radiogenic isotopes. Faure also provides problems and answers at the end of many chapters, which Dickin does not. However, I enjoyed Dickin's writing style: it is authoritative, and his historical perspective places ideas in context and provides well-paced introductions to the more difficult topics. He is also not afraid to interject his own opinion on some of the more controversial issues. Dickin's book is inevitably more up to date than the second edition of Principles of Isotope Geology (1986), and there have been significant recent developments in a number of areas including, for example, the application of U-series and Os isotopes. Dickin provides useful insights into the analytical techniques for a number of isotope systems, and overall his book is both easier to read and arguably gives a clearer insight into the nature of the subject. It is more expensive, and much of the ground covered in the two books is similar. However, now that Dickin's book is in paperback I would recommend it in terms of writing style and the material covered. It should have a major impact on the teaching of isotope geology at both undergraduate and graduate student level, as well as offering an authoritative reference book for specialists in other fields.
C. J. Hawkesworth
The Open University, UK
edited by Piero Comin-Chiaramonti and Celso de Barros Gomes. EDUSP (Editora da Universidade de São Paulo), Av. Prof. Luciano Gualberto, Travessa J, 374, 2a andar-Cidade Universitária 05508-900 São Paulo, SP Brazil, 1995. ISBN 8 531 40326 6. 464 pp. US$60.00.
Paraguay is one of the few remaining countries of the world for which there are no widely available detailed geological maps. Furthermore, the published international literature for the Early Proterozoic to Tertiary geology of the country is extremely limited. This reflects the political upheavals of Paraguay and the associated problems with access, rather than the geological significance of the rocks. The exposure in western Paraguay is limited to small outcrops in the Chaco but, to date, none of these have been recorded as alkaline igneous rocks. These appear to be concentrated in eastern Paraguay, where they are both voluminous and have a widespread distribution. They range from Permo-Triassic to Tertiary in age and exhibit a wide diversity in composition that includes leucitites, nephelinites, syenites, phonolites and carbonatites. Regionally, the Cretaceous alkaline rocks of Paraguay are significant because they represent part of the voluminous magmatism that was associated with the break-up of western Gondwana.
Alkaline Magmatism in Central-Eastern Paraguay consists of a compilation of 15 papers that have been incorporated into eight chapters. These have been written by a team of predominantly Italian, Brazilian and Australian scientists. The first chapter provides an introduction to the geology of central-eastern Paraguay and discusses the Phanerozoic tectonic and palaeogeographic evolution of the region. It includes a review of the main occurrences of the Permo-Triassic to Tertiary alkaline magmatism in northern, north-east and central Paraguay, and contains descriptions of field locations. The second chapter contains papers on the geophysical aspects of eastern Paraguay and adjacent regions. Seismic data for the western part of the region are discussed in relation to tectonic forces operating on the west coast of South America. The results of apatite fission track analysis are used to discuss the thermal history of the spatially associated Paraná sedimentary basin, and palaeomagnetic data are also presented for igneous rocks from the central alkaline province. Chapters 3 and 4 contain five papers on the petrography and mineral chemistry of the Early Cretaceous and Tertiary alkaline igneous rocks from the Asuncion-Sapucai graben in central Paraguay. These include both potassic and sodic magma types. Variations in the whole-rock chemistry together with Sr- and Nd-isotopic ratios of the Early Cretaceous potassic rocks are discussed in Chapters 5 and 6. Radiometric age determinations and whole-rock geochemistry of the Permo-Triassic alkaline igneous rocks (mainly syenites) are presented in Chapter 7. The final chapter compares the whole-rock geochemistry and isotopic ratios of the Cretaceous Paraguayan alkaline igneous rocks with contemporaneous occurrences in Brazil and Angola. Additionally, the book includes 140 pages of appendices that contain a large amount of field, petrographic and analytical data.
In summary, Alkaline Magmatism in Central-Eastern Paraguay is of interest to scientists involved in various aspects of South American geology and also Gondwana break-up. My main criticism of the book is that many of the papers are concerned with describing the very large quantity of data that has been acquired, rather than interpreting it in terms of the underlying tectonomagmatic processes, i.e. rifting and mantle plumes. As a consequence, most of the papers contain few references to research that has been undertaken on similar igneous rocks elsewhere in the world or to the results of relevant theoretical studies. A disappointment of the book is its flimsy cover. At $60, however, Alkaline Magmatism in Central-Eastern Paraguay provides a helpful reference source for all those interested in alkaline igneous rocks and is a useful addition to any library.
Sally A. Gibson
University of Cambridge, UK
