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The mid-oceanic ridges: Mountains below sea level
224
Book Reviews/Marine Geology 128 (1995) 221-226
chapter, but later go on to stress the importance of using non-genetic terms before making an interpretation concerning process or environment. This inconsistency is baffling, and could be confusing for students who have difficulty separating fact from interpretation. In addition to discussing glacial sediments per se, the authors also discuss briefly the processes and products of glaciofluvial, glaciolacustrine and periglacial environments. Chapter 3 has a section on field and laboratory methods, including stratigraphy. It is followed by a short, but useful review of dating methods, and a discussion of the wide range of techniques for studying the physical and mineralogical characteristics of sediments. In this context the methods of presenting data are adequately described for some parameters, but the manner of data-acquisition is insufficiently covered. In some cases there is an imbalance and overlap with topics covered in the following chapter, the ‘Extended Glossary’. I do not find this chapter particularly helpful. As in other institutions, we run a Quaternary course towards the end of our degree programme, and we would expect our students to have a more thorough grounding in processes and sediments than this chapter provides. Chapter 4, the ‘Extended Glossary’ is a strange compilation occupying 36 pp. It includes general geological terms and concepts which are more appropriate in a general dictionary or in a specialist text (e.g. earth’s structure and classification of folds and faults). Entries range from one sentence, to several paragraphs long including illustrations. Much of the information, such as that concerned with plotting fabric data or processing grain size distributions, is more appropriate material for the preceding chapter. The end of the book includes two pages of recommended literature, with brief paragraphs outlining its value; a list of references from which the diagrams are taken; and an index of proper names. In terms of presentation, this is an attractive book in some respects. Many figures are in colour, and the book is worth acquiring just for the fine palaeogeographical maps. Extended captions enable the reader to gain the maximum benefit from the figures. There are flaws, however. The
individual prints in photomontages do not match well, the graphic design is unexciting and fussy, and the lettering and shading on maps and diagrams are not of professional quality. How well does the book serve its intended audience? There is no doubt that for students of Quaternary science this is a very useful and readable contribution, although more thorough referencing would have been highly desirable from the perspective of our students. Nevertheless, I shall be recommending it as essential reading. It is particularly good on Quaternary history, but other elements such as glacial sedimentology are better treated elsewhere. In contrast, for the general public, this text is really too advanced. The illustrations are useful, but non-earth science readers would have difficulty getting to grips with many of the concepts. M.J. Hambrey (Liverpool)
The Mid-Oceanic Ridges: Mountains Below Sea Level. Adolphe Nicolas. Springer-Verlag, Berlin, Germany, 1995. Price: DM 58, xvii+2OOpp. (A translation of: ‘Les Montagnes sous la Mer’. Editions du BRGM, (1990); translated by: Dr. Thomas Reimer.) ISBN 3-540-57380-l. I first became acquainted with the work of Adolphe Nicolas when doing experimental geophysics at The Pennsylvania State University, and discovering his book coauthored with J.P. Poirier on: Crystalline Plasticity and Solid-state Flow in Metamorphic Rocks (John Wiley and Sons, 1976). I was impressed with his ability to move from microscopic observations of the minerals and rocks of ultramafic massifs to macroscopic reconstructions of their internal deformation, flow and emplacement. Professor Nicolas’s later leadership and deep involvement in mapping campaigns in the Semail ophilolite of Oman has produced a succession of high quality research papers describing relationships between the petrofabrics, local and regional structure, and the high-temperature flow kinematics in the deforming peridotite. These reports have provided considerable guidance to those in the geophysical and petrological com-
Book Reviews/Marine Geology 128 (1995) 221-226
munity involved in work related to mid-ocean ridge magma migration. The Oman work has, in addition, led to the production of the important research monograph: Structure of Ophiolites and Dynamics of Oceanic Lithosphere (Kluwer, New York, 1989). The present book is an English translation of the work: Les Montagnes sous la Mer (BRGM, 1990) and, like it’s French counterpart, is a lighter, more accessible companion to the Structure of Ophiolites and Dynamics of Oceanic Lithosphere. It has been prepared at the level of the Scientzjic American. The organization, scope and major chapters of the book are in the following format: In the first chapter ‘Young and living oceans’, the plate tectonic paradigm is briefly outlined. Beginning with the submarine relief mapping of Bruce C. Heezen and Marie Tharp, the chapter then outlines the origin of marine magnetic anomalies along a ridge, and then sketches the kinematics of plates as reconstructed from the paleomagnetic record. Next, the creation of ocean floor and thermal subsidence is discussed, followed by an outline of the subduction process. In ‘The Earthof convection in a heat engine’, the processes Earth’s mantle are outlined. Included are projections of seismic velocity variations in threedimensions as inferred by studies in seismic tomography, the possible relationships of subducting slabs to larger-scale convective motions, and the relationship(s) of ‘geothermal gradients’ to mantle instability and convection. In ‘The ridges-cradles of the ocean’, submarine bathymetry is the focal point, especially as it relates to ridge crests and the kinematics of the spreading process. Beginning with SEABEAM-derived physiography of the East Pacific Rise, the roles of overlapping spreading centers and off-axis seamounts in the geomorphic development of the seafloor are illustrated. Satellite altimetry, as applied to the short wavelength charting of the ocean surface, reinforces the more directly-obtained marine bathymetry and relates the sea surface elevation to the geoid. He discusses contrasting Mid-Atlantic Ridge topographic profiles to illustrate the often profound variations induced by differences in spreading rate and magma production. The chapter closes with an outline of the kinematics of fracture zones and
225
transform faults. In the chapter ‘Submarine exploration’, the use of submersibles in ridge crest and fracture zone exploration is illustrated, as well as commentary on other exploration techniques. Through the eyes of the Nautile, the Vema fracture zone is explored, and a complete crust-to-mantle cross-section assembled, with a discussion of the succession of rock types. The role of seismology is illustrated in constraining the ridge structural framework, including the depth to the Moho, the magma reservoir’s base and roof, and the reservoir’s alongand across-strike geometry. Hydrothermal activity in the ridge crest is illustrated with the Alvin-assisted marine biology discoveries on the East Pacific Rise with special focus being placed, of course, on the newlydiscovered life forms nourished by the hydrothermal vents themselves. In ‘Ophiolites-or in search of lost oceans’, the Oman ophiolite forms the chapter centerpiece, and it is used to illustrate the lithology and tectonic emplacement of ophiolites in a general sense. The geodynamic environment of ophiolites as samples of the back-arc vis-a-vis mid-ocean ridge crustal sections is then sketched. This is followed by an outline of the geologic reconstruction steps in model building, using field and laboratory studies of petrofabrics. The chapter closes with a discussion of the contrasts between the lherzolitic and harzburgitic ophiolite types. In ‘Mantle metallurgy’, analogies are drawn between the development of deformation textures (lineations and foliations) in mantle peridotites and the hightemperature plasticity of hot-rolled ferrous metals. Impregnation textures produced by melts are related to the process of melt extraction from the upper mantle. Hydraulic fracturing and the largescale ascent of melt in dikes is then related to the episodic nature of the ridge-crest intrusive/eruptive cycle. In the chapter ‘The forges of vulcan in the kingdom of Neptune’, the field, theoretical and experimental evidence for periodically-spaced peridotite diapirs is discussed. The role of these diapirs in driving the subridge deformation patterns, in the process of ridge segmentation, and in the spatial organization of the melting regimes is then presented. The important transition region that separates the mantle from the layered gabbros of
226
Book Reviews/Marine
the lower crust is also discussed in terms of rock texture, melt impregnation, and the difficulty of seismically resolving the Moho directly beneath the ridge axis itself. Sub-ridge magma reservoirs are also related to the segmentation of the ridge crest, and the lithologic/materials continuum from the melt-rich upper reservoir to the crystal-rich lower reservoir is discussed in light of the additional layering induced by the lateral drag of the basal gabbros by the deeper shear tractions of a flowing asthenosphere. In ‘From rifts to fast-spreading ridges’, and using the Red Sea rift as a starting point, Nicolas contrasts the rifting process in continental interiors with that of the ocean basins. An emphasis on the important role of spreading rate, contrasts the style of oceanic crust development in the Atlantic: magmatic influxes producing temporal magma reservoirs, sheeted dike complexes and basaltic extrusives, vis-a-vis occasional exposures of the peridotite of the upper mantle in relatively magma deficient sectors. Mantle diapirism is discussed further in terms of its association with ridge segmentation and the periodic magmatic activity of ridges through time. And, in the final chapter ‘The major pulsations of the Earth’, a discussion of the breakup of Pangea retraces some of Wegener’s evidence for continental drift (e.g. : paleontological; the fit of Africa and South America) and the age-frequency relationships of ophiolites world-wide, to discuss the potential cyclic nature of ophiolite ‘production’. The book contains a forward by Claude J. Allegre, and has been produced in a 15.5 x 23.5 cm format. The paperstock is polished and of high quality. Pages are sewn in signatures,
Geology 128 (1995) 221-226
and the book opens flat for ease of reading. There are 92 figures, and they are very pleasing in their layout, and are clear, well drafted and informative. Many of these figures are colour plates-plates which give the presentation a liveliness and dynamic that is an attractive feature. The book concludes with a 7-page 90-entry glossary. Nearly all references pertain to the original figure sources, and the references are not grouped together and listed in the customary manner of research monographs. The cover is adorned with a good reproduction of the submarine relief map of the Atlantic Ocean floor by M. Tanguy de Remur after B.C. Heezen and M. Tharp. As a minor note, I found that the typos averaged about one per chapter. An index does not accompany the book. Hopefully, both these shortcomings will dissappear in any reprinting effort. Mid-ocean Ridges: Mountains below Sea Level is primarily intended for the motivated lay reader and beginning science student, and is the kind of book that one would like to see in well-stocked public libraries. Throughout the book, somewhat more detailed and technical ‘boxes’ discuss in greater depth, aspects of the general concepts and observations presented earlier. The potential uses of the book include use as a collateral reference in undergraduate courses on physical geology and introductory Earth science, use as an extra reference in undergraduate marine geology courses, or indeed, as a rather colourful companion to the author’s monograph: ‘Structure of ophiolites and dynamics of oceanic lithosphere’. I recommend it for your consideration. Michael R. Ryan (Reston, VA)
Book Reviews/Marine Geology 128 (1995) 221-226
chapter, but later go on to stress the importance of using non-genetic terms before making an interpretation concerning process or environment. This inconsistency is baffling, and could be confusing for students who have difficulty separating fact from interpretation. In addition to discussing glacial sediments per se, the authors also discuss briefly the processes and products of glaciofluvial, glaciolacustrine and periglacial environments. Chapter 3 has a section on field and laboratory methods, including stratigraphy. It is followed by a short, but useful review of dating methods, and a discussion of the wide range of techniques for studying the physical and mineralogical characteristics of sediments. In this context the methods of presenting data are adequately described for some parameters, but the manner of data-acquisition is insufficiently covered. In some cases there is an imbalance and overlap with topics covered in the following chapter, the ‘Extended Glossary’. I do not find this chapter particularly helpful. As in other institutions, we run a Quaternary course towards the end of our degree programme, and we would expect our students to have a more thorough grounding in processes and sediments than this chapter provides. Chapter 4, the ‘Extended Glossary’ is a strange compilation occupying 36 pp. It includes general geological terms and concepts which are more appropriate in a general dictionary or in a specialist text (e.g. earth’s structure and classification of folds and faults). Entries range from one sentence, to several paragraphs long including illustrations. Much of the information, such as that concerned with plotting fabric data or processing grain size distributions, is more appropriate material for the preceding chapter. The end of the book includes two pages of recommended literature, with brief paragraphs outlining its value; a list of references from which the diagrams are taken; and an index of proper names. In terms of presentation, this is an attractive book in some respects. Many figures are in colour, and the book is worth acquiring just for the fine palaeogeographical maps. Extended captions enable the reader to gain the maximum benefit from the figures. There are flaws, however. The
individual prints in photomontages do not match well, the graphic design is unexciting and fussy, and the lettering and shading on maps and diagrams are not of professional quality. How well does the book serve its intended audience? There is no doubt that for students of Quaternary science this is a very useful and readable contribution, although more thorough referencing would have been highly desirable from the perspective of our students. Nevertheless, I shall be recommending it as essential reading. It is particularly good on Quaternary history, but other elements such as glacial sedimentology are better treated elsewhere. In contrast, for the general public, this text is really too advanced. The illustrations are useful, but non-earth science readers would have difficulty getting to grips with many of the concepts. M.J. Hambrey (Liverpool)
The Mid-Oceanic Ridges: Mountains Below Sea Level. Adolphe Nicolas. Springer-Verlag, Berlin, Germany, 1995. Price: DM 58, xvii+2OOpp. (A translation of: ‘Les Montagnes sous la Mer’. Editions du BRGM, (1990); translated by: Dr. Thomas Reimer.) ISBN 3-540-57380-l. I first became acquainted with the work of Adolphe Nicolas when doing experimental geophysics at The Pennsylvania State University, and discovering his book coauthored with J.P. Poirier on: Crystalline Plasticity and Solid-state Flow in Metamorphic Rocks (John Wiley and Sons, 1976). I was impressed with his ability to move from microscopic observations of the minerals and rocks of ultramafic massifs to macroscopic reconstructions of their internal deformation, flow and emplacement. Professor Nicolas’s later leadership and deep involvement in mapping campaigns in the Semail ophilolite of Oman has produced a succession of high quality research papers describing relationships between the petrofabrics, local and regional structure, and the high-temperature flow kinematics in the deforming peridotite. These reports have provided considerable guidance to those in the geophysical and petrological com-
Book Reviews/Marine Geology 128 (1995) 221-226
munity involved in work related to mid-ocean ridge magma migration. The Oman work has, in addition, led to the production of the important research monograph: Structure of Ophiolites and Dynamics of Oceanic Lithosphere (Kluwer, New York, 1989). The present book is an English translation of the work: Les Montagnes sous la Mer (BRGM, 1990) and, like it’s French counterpart, is a lighter, more accessible companion to the Structure of Ophiolites and Dynamics of Oceanic Lithosphere. It has been prepared at the level of the Scientzjic American. The organization, scope and major chapters of the book are in the following format: In the first chapter ‘Young and living oceans’, the plate tectonic paradigm is briefly outlined. Beginning with the submarine relief mapping of Bruce C. Heezen and Marie Tharp, the chapter then outlines the origin of marine magnetic anomalies along a ridge, and then sketches the kinematics of plates as reconstructed from the paleomagnetic record. Next, the creation of ocean floor and thermal subsidence is discussed, followed by an outline of the subduction process. In ‘The Earthof convection in a heat engine’, the processes Earth’s mantle are outlined. Included are projections of seismic velocity variations in threedimensions as inferred by studies in seismic tomography, the possible relationships of subducting slabs to larger-scale convective motions, and the relationship(s) of ‘geothermal gradients’ to mantle instability and convection. In ‘The ridges-cradles of the ocean’, submarine bathymetry is the focal point, especially as it relates to ridge crests and the kinematics of the spreading process. Beginning with SEABEAM-derived physiography of the East Pacific Rise, the roles of overlapping spreading centers and off-axis seamounts in the geomorphic development of the seafloor are illustrated. Satellite altimetry, as applied to the short wavelength charting of the ocean surface, reinforces the more directly-obtained marine bathymetry and relates the sea surface elevation to the geoid. He discusses contrasting Mid-Atlantic Ridge topographic profiles to illustrate the often profound variations induced by differences in spreading rate and magma production. The chapter closes with an outline of the kinematics of fracture zones and
225
transform faults. In the chapter ‘Submarine exploration’, the use of submersibles in ridge crest and fracture zone exploration is illustrated, as well as commentary on other exploration techniques. Through the eyes of the Nautile, the Vema fracture zone is explored, and a complete crust-to-mantle cross-section assembled, with a discussion of the succession of rock types. The role of seismology is illustrated in constraining the ridge structural framework, including the depth to the Moho, the magma reservoir’s base and roof, and the reservoir’s alongand across-strike geometry. Hydrothermal activity in the ridge crest is illustrated with the Alvin-assisted marine biology discoveries on the East Pacific Rise with special focus being placed, of course, on the newlydiscovered life forms nourished by the hydrothermal vents themselves. In ‘Ophiolites-or in search of lost oceans’, the Oman ophiolite forms the chapter centerpiece, and it is used to illustrate the lithology and tectonic emplacement of ophiolites in a general sense. The geodynamic environment of ophiolites as samples of the back-arc vis-a-vis mid-ocean ridge crustal sections is then sketched. This is followed by an outline of the geologic reconstruction steps in model building, using field and laboratory studies of petrofabrics. The chapter closes with a discussion of the contrasts between the lherzolitic and harzburgitic ophiolite types. In ‘Mantle metallurgy’, analogies are drawn between the development of deformation textures (lineations and foliations) in mantle peridotites and the hightemperature plasticity of hot-rolled ferrous metals. Impregnation textures produced by melts are related to the process of melt extraction from the upper mantle. Hydraulic fracturing and the largescale ascent of melt in dikes is then related to the episodic nature of the ridge-crest intrusive/eruptive cycle. In the chapter ‘The forges of vulcan in the kingdom of Neptune’, the field, theoretical and experimental evidence for periodically-spaced peridotite diapirs is discussed. The role of these diapirs in driving the subridge deformation patterns, in the process of ridge segmentation, and in the spatial organization of the melting regimes is then presented. The important transition region that separates the mantle from the layered gabbros of
226
Book Reviews/Marine
the lower crust is also discussed in terms of rock texture, melt impregnation, and the difficulty of seismically resolving the Moho directly beneath the ridge axis itself. Sub-ridge magma reservoirs are also related to the segmentation of the ridge crest, and the lithologic/materials continuum from the melt-rich upper reservoir to the crystal-rich lower reservoir is discussed in light of the additional layering induced by the lateral drag of the basal gabbros by the deeper shear tractions of a flowing asthenosphere. In ‘From rifts to fast-spreading ridges’, and using the Red Sea rift as a starting point, Nicolas contrasts the rifting process in continental interiors with that of the ocean basins. An emphasis on the important role of spreading rate, contrasts the style of oceanic crust development in the Atlantic: magmatic influxes producing temporal magma reservoirs, sheeted dike complexes and basaltic extrusives, vis-a-vis occasional exposures of the peridotite of the upper mantle in relatively magma deficient sectors. Mantle diapirism is discussed further in terms of its association with ridge segmentation and the periodic magmatic activity of ridges through time. And, in the final chapter ‘The major pulsations of the Earth’, a discussion of the breakup of Pangea retraces some of Wegener’s evidence for continental drift (e.g. : paleontological; the fit of Africa and South America) and the age-frequency relationships of ophiolites world-wide, to discuss the potential cyclic nature of ophiolite ‘production’. The book contains a forward by Claude J. Allegre, and has been produced in a 15.5 x 23.5 cm format. The paperstock is polished and of high quality. Pages are sewn in signatures,
Geology 128 (1995) 221-226
and the book opens flat for ease of reading. There are 92 figures, and they are very pleasing in their layout, and are clear, well drafted and informative. Many of these figures are colour plates-plates which give the presentation a liveliness and dynamic that is an attractive feature. The book concludes with a 7-page 90-entry glossary. Nearly all references pertain to the original figure sources, and the references are not grouped together and listed in the customary manner of research monographs. The cover is adorned with a good reproduction of the submarine relief map of the Atlantic Ocean floor by M. Tanguy de Remur after B.C. Heezen and M. Tharp. As a minor note, I found that the typos averaged about one per chapter. An index does not accompany the book. Hopefully, both these shortcomings will dissappear in any reprinting effort. Mid-ocean Ridges: Mountains below Sea Level is primarily intended for the motivated lay reader and beginning science student, and is the kind of book that one would like to see in well-stocked public libraries. Throughout the book, somewhat more detailed and technical ‘boxes’ discuss in greater depth, aspects of the general concepts and observations presented earlier. The potential uses of the book include use as a collateral reference in undergraduate courses on physical geology and introductory Earth science, use as an extra reference in undergraduate marine geology courses, or indeed, as a rather colourful companion to the author’s monograph: ‘Structure of ophiolites and dynamics of oceanic lithosphere’. I recommend it for your consideration. Michael R. Ryan (Reston, VA)