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Enclaves and Granite Petrology. Developments in Petrology, 13.
158
BOOKREVIEWS
surprising that the true (and perhaps commonest) vibrational absorption technique of infrared spectroscopy is not given the place it deserves within such a volume. As a final comment, it should be said that the complementary character of the spectroscopies described within this volume could be emphasized much more strongly, perhaps this should have fallen to the editors. Instead the Editors arrive at the somewhat exasperating conclusion (within their preface) that X-ray diffraction is "still the best research tool available". Such value judgements cannot really be helpful (or even properly justified to my mind). While the Editors seem set in their ways, it is to be hoped that this volume will succeed in persuading at least some of its readers that a full appreciation of the structure and behaviour of minerals depends not simply on diffraction methods, but also the spectrum of spectroscopic techniques which reveal the fundamental characteristics of structure on a broader set of length and time scales. SIMON A.T. REDFERN (Manchester)
Enclaves and Granite Petrology. Developments in Petrology, 13. Edited by J. Didier and B. Barbarin, Elsevier Science Publishers, Amsterdam, The Netherlands, 1991. Hardcover. xxiv+ 600 pp. Price US$ 143.50/Dfl. 280.-- ISBN 9-44489145=5. Any xenolith, xenocryst, screen, schlieren or other bundle clot, knot or globule of cumulate or noticeably clark segregation can be an enclave. A term first coined by Alfred Lacroi ( 1863-1948 ) to designate a patch or dollop of rock isolated within a larger, continuum mass of rock, the use of enclave is now commonplace. More often than not, enclaves are mafic-looking, fine grained bodies within intermediate and granitic plutonic rocks. They are always points of conversation in the field and the inevitable arguments cover all the petrogenetic bases. Simply put, are enclaves merely the gristle left from the incomplete chewing of magmatic mixing? Are they intimate vestiges of the very origin of the granitoid itself?. Or are they merely accidental incidents in a long history of ascension and solidification? Until about twenty years ago the answers to these ques-
tions, although hotly debated, were not considered first rank petrological worries. They still may not be, but they are now recognizably important issues. Enclaves clearly provide crucial telltale information on the origin and evolution of granitoids. Unlike volcanic rocks, which through eruption and quenching represent explicit snapshots of magmatic time, the slow cooling and sliding reequilibration ofplutonic solidification, in essence, bakesout any explicitly restricted record of time and temperature. Plutons asymptotically achieve a final crystalline state carrying a fully integrated solidification history. Different magma compositions have different time-temperature-composition histories, and in this sense enclaves function essentially as magmatic spikes enabling the physical and chemical evolution of granitoids to be internally gauged. It is a big job to study and read the varied and complex nature of enclaves. These thirty nine chapters represent a comprehensive treatment of all aspects of the physical, chemical and historical petrology of enclaves. It is a characteristic Elsevier petrology book of normal size, with a shiney blue and black igneous photomicrograph as a cover; the paper is of good quality, white, and acid free; the page numbers are useful and where they should be. There are excellent subject and author indexes and a comprehensive bibliography. The type is clear, well set and virtually error-free. The science itself is heavily descriptive and oriented towards case studies of mafic microgranular enclaves (MME's). There are fifteen chapters of case studies, three of introductory material, seven on the main features of MME's, nine on MME genesis and evolution, four on other types of enclaves, and a single concluding chapter. Although the editors clearly have made no effort to blend, homogenize, or arbitrate the various contributions, it all fits together rather well. (In this sense, this collection resembles the subject itself.) Each chapter is concise, much to the point, and opened and closed with succinct introductory and concluding sections. Many chapters are so explicit and clear in presentation that they will be especially useful to students and nonenclavists. Completeness has been achieved apparently by encouraging contributors to provide concise summary chapters of more extensive work published elsewhere. This is a pleasing alternative
159
BOOK REVIEWS
to voluminous, repository-style presentations so common in such large undertakings. Evidence for and against almost every likely scenario of enclave formation is given, but some fare significantly better than others. Restites, autoliths and blobs of precursory basalt seem to edge ahead of reworked xenoliths, disrupted fine-grained bodies, and magma mixing as dominant sources of enclaves. The evidence is mainly petrographic bolstered by some chemical (major and trace element and isotopic) information. There are striking correlations between enclave SiO2 and fi~80 and remarkable and clear and systematic divisions between the bulk compositions of enclaves and their hosts. Isotopic equilibrium is the general rule in all except the largest enclaves, which makes them especially useful for dating the more homogeneous host granitoids. There is a surprising dearth of analysis via chemical reactions and the attendant thermodynamics. This is in striking contrast to present trends in both metamorphic and igneous petrology at large. There is a clear appreciation here and there of this rigor, as well as that of kinetics, but this is clearly a future direction for enclave petrology. In some distinct ways the more quantitative physical or dynamical aspects of enclave genesis (especially via magma mingling) are much more advanced than are the chemical aspects. In sum, it is a pleasure to see crisp, clean photomicrographs and insightful accompanying descriptions by authors who know the value and gravity of a petrology based firmly on petrographic, field and chemical evidence. The stage is certainly set with this volume for enclaves to become a household tool to gain insight into granitoid petrogenesis. Didier and Barbarin are to be commended for a momentous and worthwhile task well done. B.D. MARSH (Baltimore, MD)
The Colours of Opaque Minerals by A. Peckett, J. Wiley & Sons, Chichester, U.K., 1992. It isn't often that topics like covelline and colour t.v. or pyrite and paint pigments appear side by side in a textbook. But here diverse examples abound as Andrew Peckett leads the reader on a delightful
journey of discovery as he answers the question "Why do opaque minerals have the colours we see?". This book is the fruit of work begun by Norman Henry and Roy Phillips. Sadly they have not lived to see its fine final form, which has been engineered by Andrew Peckett. The pen passed on to him and he has produced a well-written and stimulating text. Split into two parts, it deals first with the theory of colour in opaque minerals and then provides around 270 examples of such minerals in the form of a data compendium. The whole is attractively and clearly presented, and is accompanied by helpful figures, appendices, and indices. I am not an ore microscopist myself, and so was rather nervous at taking on the task of reviewing this book. The diversity of the discussion, however, should quickly attract any reader and it holds interest splendidly. Before even reaching the main text, colour plates demonstrate a number o f " o p t i c a l illusions" which quickly convince that human visual senses are frail and fickle. The description and judgement of colour in minerals is by no means a straightforward procedure. Perception and measurement ofcolour, therefore, form the thrust of the first two chapters. Mankind's theories of the nature of light, from Euclid to Einstein, are first reviewed and the foundations laid down. The style is entertaining and didactic. The content will interest a wide audience, especially the treatment of perception, the neuro-physiology and psychology of vision, and the abundant examples which season the text. I can see these coming in useful for the trivia quiz comp6re: "what is daltonism, and why is it so-called?", "is a rag red to a bull?", "why is the sky more blue when you're young?". Whatever else, it becomes clear that measurement more accurate than our senses, in the form of quantitative chromaticity schemes, is essential for the characterisation of opaque minerals. The chapters on the interaction of light with crystals will be useful to teachers and students alike. Little is left unsaid, prior knowledge is not assumed, and the text is well structured so that at each point the reader is given all that is needed to make the next step in understanding. Aspects of physics which many geology students will not have met before are presented in an unfrightening manner, to the level of introductory undergraduate physics. The mathematical concepts used are all reviewed in an appendix, with exercises provided to aid their comprehension.
BOOKREVIEWS
surprising that the true (and perhaps commonest) vibrational absorption technique of infrared spectroscopy is not given the place it deserves within such a volume. As a final comment, it should be said that the complementary character of the spectroscopies described within this volume could be emphasized much more strongly, perhaps this should have fallen to the editors. Instead the Editors arrive at the somewhat exasperating conclusion (within their preface) that X-ray diffraction is "still the best research tool available". Such value judgements cannot really be helpful (or even properly justified to my mind). While the Editors seem set in their ways, it is to be hoped that this volume will succeed in persuading at least some of its readers that a full appreciation of the structure and behaviour of minerals depends not simply on diffraction methods, but also the spectrum of spectroscopic techniques which reveal the fundamental characteristics of structure on a broader set of length and time scales. SIMON A.T. REDFERN (Manchester)
Enclaves and Granite Petrology. Developments in Petrology, 13. Edited by J. Didier and B. Barbarin, Elsevier Science Publishers, Amsterdam, The Netherlands, 1991. Hardcover. xxiv+ 600 pp. Price US$ 143.50/Dfl. 280.-- ISBN 9-44489145=5. Any xenolith, xenocryst, screen, schlieren or other bundle clot, knot or globule of cumulate or noticeably clark segregation can be an enclave. A term first coined by Alfred Lacroi ( 1863-1948 ) to designate a patch or dollop of rock isolated within a larger, continuum mass of rock, the use of enclave is now commonplace. More often than not, enclaves are mafic-looking, fine grained bodies within intermediate and granitic plutonic rocks. They are always points of conversation in the field and the inevitable arguments cover all the petrogenetic bases. Simply put, are enclaves merely the gristle left from the incomplete chewing of magmatic mixing? Are they intimate vestiges of the very origin of the granitoid itself?. Or are they merely accidental incidents in a long history of ascension and solidification? Until about twenty years ago the answers to these ques-
tions, although hotly debated, were not considered first rank petrological worries. They still may not be, but they are now recognizably important issues. Enclaves clearly provide crucial telltale information on the origin and evolution of granitoids. Unlike volcanic rocks, which through eruption and quenching represent explicit snapshots of magmatic time, the slow cooling and sliding reequilibration ofplutonic solidification, in essence, bakesout any explicitly restricted record of time and temperature. Plutons asymptotically achieve a final crystalline state carrying a fully integrated solidification history. Different magma compositions have different time-temperature-composition histories, and in this sense enclaves function essentially as magmatic spikes enabling the physical and chemical evolution of granitoids to be internally gauged. It is a big job to study and read the varied and complex nature of enclaves. These thirty nine chapters represent a comprehensive treatment of all aspects of the physical, chemical and historical petrology of enclaves. It is a characteristic Elsevier petrology book of normal size, with a shiney blue and black igneous photomicrograph as a cover; the paper is of good quality, white, and acid free; the page numbers are useful and where they should be. There are excellent subject and author indexes and a comprehensive bibliography. The type is clear, well set and virtually error-free. The science itself is heavily descriptive and oriented towards case studies of mafic microgranular enclaves (MME's). There are fifteen chapters of case studies, three of introductory material, seven on the main features of MME's, nine on MME genesis and evolution, four on other types of enclaves, and a single concluding chapter. Although the editors clearly have made no effort to blend, homogenize, or arbitrate the various contributions, it all fits together rather well. (In this sense, this collection resembles the subject itself.) Each chapter is concise, much to the point, and opened and closed with succinct introductory and concluding sections. Many chapters are so explicit and clear in presentation that they will be especially useful to students and nonenclavists. Completeness has been achieved apparently by encouraging contributors to provide concise summary chapters of more extensive work published elsewhere. This is a pleasing alternative
159
BOOK REVIEWS
to voluminous, repository-style presentations so common in such large undertakings. Evidence for and against almost every likely scenario of enclave formation is given, but some fare significantly better than others. Restites, autoliths and blobs of precursory basalt seem to edge ahead of reworked xenoliths, disrupted fine-grained bodies, and magma mixing as dominant sources of enclaves. The evidence is mainly petrographic bolstered by some chemical (major and trace element and isotopic) information. There are striking correlations between enclave SiO2 and fi~80 and remarkable and clear and systematic divisions between the bulk compositions of enclaves and their hosts. Isotopic equilibrium is the general rule in all except the largest enclaves, which makes them especially useful for dating the more homogeneous host granitoids. There is a surprising dearth of analysis via chemical reactions and the attendant thermodynamics. This is in striking contrast to present trends in both metamorphic and igneous petrology at large. There is a clear appreciation here and there of this rigor, as well as that of kinetics, but this is clearly a future direction for enclave petrology. In some distinct ways the more quantitative physical or dynamical aspects of enclave genesis (especially via magma mingling) are much more advanced than are the chemical aspects. In sum, it is a pleasure to see crisp, clean photomicrographs and insightful accompanying descriptions by authors who know the value and gravity of a petrology based firmly on petrographic, field and chemical evidence. The stage is certainly set with this volume for enclaves to become a household tool to gain insight into granitoid petrogenesis. Didier and Barbarin are to be commended for a momentous and worthwhile task well done. B.D. MARSH (Baltimore, MD)
The Colours of Opaque Minerals by A. Peckett, J. Wiley & Sons, Chichester, U.K., 1992. It isn't often that topics like covelline and colour t.v. or pyrite and paint pigments appear side by side in a textbook. But here diverse examples abound as Andrew Peckett leads the reader on a delightful
journey of discovery as he answers the question "Why do opaque minerals have the colours we see?". This book is the fruit of work begun by Norman Henry and Roy Phillips. Sadly they have not lived to see its fine final form, which has been engineered by Andrew Peckett. The pen passed on to him and he has produced a well-written and stimulating text. Split into two parts, it deals first with the theory of colour in opaque minerals and then provides around 270 examples of such minerals in the form of a data compendium. The whole is attractively and clearly presented, and is accompanied by helpful figures, appendices, and indices. I am not an ore microscopist myself, and so was rather nervous at taking on the task of reviewing this book. The diversity of the discussion, however, should quickly attract any reader and it holds interest splendidly. Before even reaching the main text, colour plates demonstrate a number o f " o p t i c a l illusions" which quickly convince that human visual senses are frail and fickle. The description and judgement of colour in minerals is by no means a straightforward procedure. Perception and measurement ofcolour, therefore, form the thrust of the first two chapters. Mankind's theories of the nature of light, from Euclid to Einstein, are first reviewed and the foundations laid down. The style is entertaining and didactic. The content will interest a wide audience, especially the treatment of perception, the neuro-physiology and psychology of vision, and the abundant examples which season the text. I can see these coming in useful for the trivia quiz comp6re: "what is daltonism, and why is it so-called?", "is a rag red to a bull?", "why is the sky more blue when you're young?". Whatever else, it becomes clear that measurement more accurate than our senses, in the form of quantitative chromaticity schemes, is essential for the characterisation of opaque minerals. The chapters on the interaction of light with crystals will be useful to teachers and students alike. Little is left unsaid, prior knowledge is not assumed, and the text is well structured so that at each point the reader is given all that is needed to make the next step in understanding. Aspects of physics which many geology students will not have met before are presented in an unfrightening manner, to the level of introductory undergraduate physics. The mathematical concepts used are all reviewed in an appendix, with exercises provided to aid their comprehension.