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Kimberlites and their xenoliths
97 including major and trace elements, ranging f r o m the group I to V I I in the periodic table, excepting the rare gas elements. The last t w o papers by Allegre et al. and O'Nions et al. are devoted to the modelling of the process of evolution of the earth's mantle on the basis of radiogenic isotope systematics. In the middle of the 16 papers presenting mantle heterogeneity M.J. O'Hara (p. 72) gave a cautious warning about the estimation of the effect of crustal contamination to the magma. An evidence of mantle heterogeneity can be estimated from the samples of mantle-derived materials by eliminating the effect of partial melting, fractional crystallization, crustal contamination etc. If an unknown process or inestimable effect of a process that changes elemental composition is involved in the process of formation of the sample material, mantle heterogeneity can be incorrectly estimated. Thus, it appears to be a right place to discuss such difficult-to-estimate effect of crustal contamination. In fact, even the radiogenic isotope systematics which is thought to be one of the most reliable methods to study mantle evolution show discrepancies. For example, Nd isotopes indicate a rather homogeneous Precambrian mantle, Sr isotopes show a little more dispersion, whole Pb isotopes indicate a heterogeneity comparable to the modern mantle (B. Jahn et al., p. 227; Allegre et al., p. 312). D.K. Bailey discussed that early catastrophic melting and degassing of the earth's lithosphere is improbable based on the evidence on the gaseous elements, H and C. However, the opposite is suggested from A r isotope ratios (e.g., Ozima, Geochim. Cosmochim, Acta, 39: 1127; 1975). If the observed heterogeneity is mostly due to mantle--crust interaction such as rapid recycling of the crustal material, then the heterogeneity is independent of the initial conditon of the mantle. If, on the other hand, it was produced in the mantle w i t h o u t a large contribution of the crustal material, the initial chemical condition is a major concern for the origin of the heterogeneity. In this c o n t e x t a discussion on the possible early catastrophic evolution of the lithosphere from different aspects may well be included in this book, although it is not a
main subject of the meeting. Overall this is a good b o o k as the source of geochemistry of the mantle based on the mantle-derived materials; however, you may be disappointed if you were more interested in knowing the origin and evolution of the mantle heterogeneity rather than to glance at the present state of the geochemical study of the earth's mantle. Hiroshi Nagasawa, T o k y o
J. Barry Dawson, 1980. Kimberlites and their Xenofiths. Minerals and Rocks, 15, Springer-Verlag, Berlin, X II + 252 pp., cloth: DM 88.00, approx. US $52.00. Kimberlites are derived from deep within the mantle and carry not only diamonds, but also much potential information about their source. Accordingly, they have been the subject of much scientific, as well as economic interest, not least on account of their bizarre trace element chemistry. A very large amount of mineralogical petrological and geochemical work has been carried out in recent years. This followed on from the classic works of Wagner (The Diamond Fields o f Southern Africa, 1914) and Williams (The Genesis o f the Diamond, 1932), both of which are still well worth reading. T w o international conferences, in 1973 and 1977, have been held on kimberlites, with a third scheduled for 1982. Accordingly a vast, but scattered literature has appeared and the time is ripe for a synthesis of this and of our existing knowledge of kimberlite. This task has been carried out with great competence by the author, who has drawn on many years experience to provide a readable and authoritative account fit to stand alongside the works of Wagner and Williams. Following an introductory chapter, nine chapters cover distribution and tectonic setting, geology, petrography, geochemistry mineralogy, xenoliths, megacrysts, the mantle, and kimberlite genesis. In its scope and treatment of the subject, this reviewer is reminded of Brian Mason's classic text on meteorites (1962). Dawson has provided a wealth of information. There are useful tables of analytical data for major and trace elements
98 not only for kimberlites and their minerals, but also for the many xenolith suites, including bot~q rock and mineral analyses. This body of data alone is worth the price of the b o o k and will no doubt be mined by grateful geochemists for many years. The author concentrates mainly on facts and wisely refrains from too much speculation about the mantle. In the final chapter he comes down in favor of an origin for kimberlites by partial melting of a phlogopite-bearing garnet Iherzolite at depths of up to 3 0 0 k m . He rejects both the zone refining model of Harris and the residual fractional crystallisation models. He concludes that carbonatites and kimberlites are not genetically related, but is neutral on the question of whether diamonds are phenocrystal or xenocrystal in kimberlites. He favors the theory that 'the basic granutites (lower crustal xenoliths in kimberlites) represent the residuum of rocks of more intermediate composition that have been subjected to an anatectic melting event during which the granitic constituents migrated into the upper crust' (p. 210). There are a few annoying misprints (even diamond is mis-spelt on p. 218!) and the subject index (13 pages comprising 24 principal entries) is quite inadequate. However, the reference list of over 600 entries should satisfy even the aficionados of kimberlites. Not much is missed, despite a disclaimer in the Preface. This book should be read and understood by all students of the mantle since it represents the distilled wisdom of much experience. When they have accomplished this task, readers may find it profitable to refer their wives or girlfriends to the useful seven page section on diamonds. S.R. Taylor, Canberra, A.C.T.
Francis J. Turner, 1981. Metamorphic Petrology- Mineralogical, Field, and Tectonic Aspects, 2nd ed. International Series in the Earth and Planetary Sciences. McGraw-Hill Book Co. GmbH, Hamburg, xv + 524 pp., DM 80.90 (hardcover). This a completely revised and expanded edition of Professor Turner's well-known
book, published in 1968, but in a sense it is a sixth edition of a book on metamorphism first published in 1948. The recurring theme in all of these contributions to petrology is the concept of metamorphic facies, which originated with Eskola in 1915. Although many modern petrologists pay little attention to the facies concept, and some have abandoned it outright, all will agree that the concept has played an important role in the development of metamorphic petrology. In particular, it provided a stimulus for the study of variation in metamorphic grade, as revealed by mineral assemblages, and has raised questions concerning the temperature and pressure of metamorphism, which have provided an incentive for much experimental w o r k on phase equilibrium. Also, the facies concept, in its most general form, provided compelling evidence for the attainment of chemical equilibrium in rocks, in obeyance to the laws of Nature. These are the topics that Professor Turner discusses at length in his new book. Numerous field examples are recorded of both contact and regional metamorphism, including several new examples of progressive metamorphism in Precambrian terranes, and a summary of ocean-floor metamorphism. Several experimental and thermochemical phase relations are presented, particularly those that are most useful in providing limits to temperature and pressure, and a few of the many proposed 'geothermometers' are included. In addition, the author has devoted much more attention than previously to tectonic aspects of metamorphism, i.e., to metamorphism as a natural process occurring sporadically and periodically in response to different geothermal gradients in different tectonic environments. This aspect of the book should be of interest to geologists concerned with global tectonics and the development of the earth's crust. Although the facies concept forms a convenient base from which to explore metamorphism, it tends to impose restrictions on the kind of questions that are asked. This approach defines the goal of metamorphic petrology as the determination of the temperature and pressure of metamorphism, which is quite different from that which attempts to understand metamorphic
main subject of the meeting. Overall this is a good b o o k as the source of geochemistry of the mantle based on the mantle-derived materials; however, you may be disappointed if you were more interested in knowing the origin and evolution of the mantle heterogeneity rather than to glance at the present state of the geochemical study of the earth's mantle. Hiroshi Nagasawa, T o k y o
J. Barry Dawson, 1980. Kimberlites and their Xenofiths. Minerals and Rocks, 15, Springer-Verlag, Berlin, X II + 252 pp., cloth: DM 88.00, approx. US $52.00. Kimberlites are derived from deep within the mantle and carry not only diamonds, but also much potential information about their source. Accordingly, they have been the subject of much scientific, as well as economic interest, not least on account of their bizarre trace element chemistry. A very large amount of mineralogical petrological and geochemical work has been carried out in recent years. This followed on from the classic works of Wagner (The Diamond Fields o f Southern Africa, 1914) and Williams (The Genesis o f the Diamond, 1932), both of which are still well worth reading. T w o international conferences, in 1973 and 1977, have been held on kimberlites, with a third scheduled for 1982. Accordingly a vast, but scattered literature has appeared and the time is ripe for a synthesis of this and of our existing knowledge of kimberlite. This task has been carried out with great competence by the author, who has drawn on many years experience to provide a readable and authoritative account fit to stand alongside the works of Wagner and Williams. Following an introductory chapter, nine chapters cover distribution and tectonic setting, geology, petrography, geochemistry mineralogy, xenoliths, megacrysts, the mantle, and kimberlite genesis. In its scope and treatment of the subject, this reviewer is reminded of Brian Mason's classic text on meteorites (1962). Dawson has provided a wealth of information. There are useful tables of analytical data for major and trace elements
98 not only for kimberlites and their minerals, but also for the many xenolith suites, including bot~q rock and mineral analyses. This body of data alone is worth the price of the b o o k and will no doubt be mined by grateful geochemists for many years. The author concentrates mainly on facts and wisely refrains from too much speculation about the mantle. In the final chapter he comes down in favor of an origin for kimberlites by partial melting of a phlogopite-bearing garnet Iherzolite at depths of up to 3 0 0 k m . He rejects both the zone refining model of Harris and the residual fractional crystallisation models. He concludes that carbonatites and kimberlites are not genetically related, but is neutral on the question of whether diamonds are phenocrystal or xenocrystal in kimberlites. He favors the theory that 'the basic granutites (lower crustal xenoliths in kimberlites) represent the residuum of rocks of more intermediate composition that have been subjected to an anatectic melting event during which the granitic constituents migrated into the upper crust' (p. 210). There are a few annoying misprints (even diamond is mis-spelt on p. 218!) and the subject index (13 pages comprising 24 principal entries) is quite inadequate. However, the reference list of over 600 entries should satisfy even the aficionados of kimberlites. Not much is missed, despite a disclaimer in the Preface. This book should be read and understood by all students of the mantle since it represents the distilled wisdom of much experience. When they have accomplished this task, readers may find it profitable to refer their wives or girlfriends to the useful seven page section on diamonds. S.R. Taylor, Canberra, A.C.T.
Francis J. Turner, 1981. Metamorphic Petrology- Mineralogical, Field, and Tectonic Aspects, 2nd ed. International Series in the Earth and Planetary Sciences. McGraw-Hill Book Co. GmbH, Hamburg, xv + 524 pp., DM 80.90 (hardcover). This a completely revised and expanded edition of Professor Turner's well-known
book, published in 1968, but in a sense it is a sixth edition of a book on metamorphism first published in 1948. The recurring theme in all of these contributions to petrology is the concept of metamorphic facies, which originated with Eskola in 1915. Although many modern petrologists pay little attention to the facies concept, and some have abandoned it outright, all will agree that the concept has played an important role in the development of metamorphic petrology. In particular, it provided a stimulus for the study of variation in metamorphic grade, as revealed by mineral assemblages, and has raised questions concerning the temperature and pressure of metamorphism, which have provided an incentive for much experimental w o r k on phase equilibrium. Also, the facies concept, in its most general form, provided compelling evidence for the attainment of chemical equilibrium in rocks, in obeyance to the laws of Nature. These are the topics that Professor Turner discusses at length in his new book. Numerous field examples are recorded of both contact and regional metamorphism, including several new examples of progressive metamorphism in Precambrian terranes, and a summary of ocean-floor metamorphism. Several experimental and thermochemical phase relations are presented, particularly those that are most useful in providing limits to temperature and pressure, and a few of the many proposed 'geothermometers' are included. In addition, the author has devoted much more attention than previously to tectonic aspects of metamorphism, i.e., to metamorphism as a natural process occurring sporadically and periodically in response to different geothermal gradients in different tectonic environments. This aspect of the book should be of interest to geologists concerned with global tectonics and the development of the earth's crust. Although the facies concept forms a convenient base from which to explore metamorphism, it tends to impose restrictions on the kind of questions that are asked. This approach defines the goal of metamorphic petrology as the determination of the temperature and pressure of metamorphism, which is quite different from that which attempts to understand metamorphic