Journal of Petrology Volume 41 Number 12 Pages 1824-1825 2000
© Oxford University Press 2000
BOOK REVIEW |
Mantle Petrology: Field Observations and High Pressure Experimentation (a Tribute to Francis R. (Joe) Boyd) edited by Y. Fei, C. M. Bertka and B. O. Mysen. Geochemical Society Special Publication 6. The Geochemical Society, Houston, TX, 1999. 322 pp. ISBN 0941809056. US$55 for members; $85 for non-members
Joe Boyd, a stalwart of petrology, officially retired from the Geophysical Laboratory in 1996 after 43 years of service. In an effort to immortalize this event in the annals of petrology, Boyd’s colleagues organized a symposium, which resulted in this edited volume. Joe Boyd’s versatility is legendary: his contribution ranges from ’hard core’ experimental petrology and to field and laboratory based studies. Boyd’s pioneering work on the nature of the Earth’s mantle has inspired many, including this writer, to fall in love with those tiny gifts from the mantle, packaged as ’xenoliths’, brought to the surface by lavas. Understandably, the editors, all of whom are theoreticians and experimentalists, tried to organize this volume in such a way that it appropriately reflects Boyd’s research interests, and divided the various contributions into ’Field Observations’ and ’High-Pressure Experimentation’ categories. In a sense, the title of the first group is misleading inasmuch as the papers in this category involve highly sophisticated laboratory based isotopic and trace element studies of xenoliths and thus they go far beyond being simple ’field observations’.The volume begins with an excellent synopsis of Joe Boyd’s outstanding academic career, written by none other than Hatten S. Yoder, Jr, another legend in petrology. Part 1 (Field Observations) of the book consists of eight papers. The lead article, by Rudnick & Nyblade adopts the classic Boydian approach of figuring out the thermal state of the sub-continental lithosphere from P–T equilibration conditions of mantle xenoliths brought up by kimberlites. An interesting and significant shift in the work by Rudnick & Nyblade from the earlier work by Boyd and colleagues is in its adaptation of a more modern (and presumably better) thermobarometer. Rudnick & Nyblade then proceed to obtain constraints on lithospheric heat flow and on the thickness of the continental lithosphere based on the xenolith P–T values. The second paper, by Griffin et al., revisits the issue of the compositional aspects of the continental and oceanic lithospheres, which was Boyd’s theme in his well-known 1989 paper. These authors use a much larger database than was available to Boyd over a decade ago. Griffin et al. make an attempt at addressing the issue of secular variation in various compositional characteristics of the sub-continental lithospheric mantle. The authors appear to have introduced some new acronyms that this reviewer was not aware of. Shimizu’s paper follows, with a short but strong cautionary note about how young mantle metasomatic events can significantly modify ’primary signals’, i.e. the modal and chemical characteristics of the lithosphere that would have originally derived from some very old events. Aptly, the author wonders in the end about how much of a sampling bias is introduced by the kimberlitic xenoliths and about the utility of understanding the lithosphere from xenoliths. The fourth paper, by Pearson, moves away from elemental geochemistry, which is the topic of the first three papers, to isotope geochemistry. The author provides a review of the Sr, Nd and Os isotopic composition of kimberlitic xenoliths, and visits the issue of craton formation and history of the continental lithosphere in various localities. The distinctive recording capability of the Os system (as opposed to Nd, Sr systems) of early stages of craton formation is well brought out. The next paper, by Silver et al. on petrofabric analyses of xenoliths and seismic anisotropy, is an abrupt departure from the geochemically oriented papers. These authors explore a very new area of research on continental deformation to mantle tectonic processes using somewhat classical methods of structural geology. Haggerty’s contribution offers a classic exposé on diamonds and craton formation beginning with the meaning of the term ’craton’. This author combines a variety of data, ranging from simple geographical–geological associations to sophisticated isotopic analyses, to review the origin of diamonds. Haggerty takes this opportunity to put forth his petrogenetic model that combines diamond petrogenesis with superplumes, superchrons and kimberlite formation. Harte et al. then guide the reader to a very interesting suite of ultra-deep inclusions in diamonds from a location in Brazil. These inclusions provide an exciting window into the top 100 km of the lower mantle. The next paper, by Grove et al., represents a significant departure from the previous chapters in that it looks into the origin of komatiites from a largely experimental perspective. In fact, the editors’ decision to include this paper in the ’Observations’ section (and not in the ’Experimental’ section) is somewhat surprising. The origin of komatiites and continental lithosphere evolution was a topic of some interest to Boyd, who gave it some thought in his 1989 paper. Using new and other experimental data, mainly collected in the MIT laboratory, Grove et al. present a case of generation of Archean komatiites in H2O-bearing conditions over paleo-subduction zones.
Part 2 (‘High-Pressure Experimentation’) of this book consists of eight more papers, from classical haplo-peridotite–basalts in simple analog systems to volatiles in the mantle. The first paper, by Smith, takes a close look at thermometers and barometers for upper-mantle lherzolitic assemblages and makes specific recommendation about which combination of thermometer and barometer to use. He also examines how temperatures estimated on natural lherzolites correlate with their textural and compositional aspects of equilibrium or disequilibrium (i.e. mineral zoning, isotopic disequilibrium and closure). Fei & Bertka then review experimental data that are relevant to deep mantle mineralogy and phase transitions. They start out with simple system phase relations, such as Mg2SiO4, and extend their review to natural lherzolitic bulk composition. All along they stay focused on subsolidus relations. The next contribution, by Presnall, examines the intricacies of phase relationships that would control fractional crystallization of basalt magma within the lithosphere (0–3 GPa). This review is based largely on the experimental work on the analog systems performed in his laboratory. The author then proceeds to discuss the petrogenesis of basalts erupted at mid-oceanic ridges, Hawaii and arcs. The two chapters that follow examine the origin of the cratonic lithosphere from a largely experimental perspective. Walter and Herzberg both model the nature of partial melting residues of a ’fertile’ peridotitic mantle as a function of pressure and substantiate Boyd’s earlier observation that cratonic lithosphere is generally (with at least one possible exception—Tanzanian craton) enriched in orthopyroxene. They review the plausible mechanisms that produced this enrichment: whereas Walter supports the concept of melt–wall rock (lherzolite) reaction as the mechanism for orthopyroxene enrichment, Herzberg argues that the enrichment is due to thorough mechanical mixing of orthopyroxenite cumulates and depleted olivine-rich residues of melting. Herzberg takes this a little further and argues for a connection between plume magmatism, komatiite formation and orthopyroxene enrichment of the cratonic lithosphere. The last three chapters review the phase relationships in the hydrous and carbonated mantle. Ulmer & Trommsdorff examine the stability of various hydrous phases and their breakdown reactions up to 10 GPa, whereas in the following chapter, Frost does the same at pressures in excess of 10 GPa. In the final chapter, Luth provides a review of how carbon is hosted in the mantle as a function of pressure. In the process, he examines many related issues, starting from mantle oxidation states to phase equilibrium of carbonated peridotites.
This book is 322 pages long, nicely hard bound, and is devoid of color illustrations and typographic errors. Black and white (and some grayscale relief) illustrations work well in most cases; only in one or two chapters are some illustrations a little cluttered. The publisher has made a real attempt at keeping the cost down. I like almost everything about this book and feel that every graduate student, post-doctoral fellow and professor of petrology should own a personal copy. Thanks to this journal I will cherish my own free copy!
Gautam Sen
Department of Geology, Florida International University
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