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Rift zones of the world ocean
QUATERNARY
RESEARCH
7, I&-
147 (1977)
BOOK REVIEWS Rift Zones of the World Ocean. A. P. Vinogradov and G. B. Udintsev, Eds. Halsted Press, New York, 503 p., 1975, $55.00. According to the new global tectonics, each year more than 100 cubic kilometers of material is added to the floor of the world ocean at the zone of rifting. If a disparity, temporary but long in human terms, arises in the rate at which material is removed in subduction regions, what is the effect on sea level? Might it obscure the effects of deglaciation and isostatic rebound? What is the nature of the sediment found to be accumulating in certain sectors of the rift? What is the disposition of “pollution” added to ocean waters at the rift axis? If activity at the rift axis is any indication, processes of internal origin may play a larger role than expected in the geology of the recent past. The title of this densely packed, valuable volume appearing under the auspices of Vinogradov and Udintsev is a misnomer. Only three chapters treat of the oceanic rift system as a whole. These serve to relate its essential contents, an account of Soviet investigations of the floor of the Indian Ocean, to the world rift system. Nineteen chapters in all recount the coverage and results obtained in the Indian Ocean during the 36th and 41st cruises of the R. V. Vityaz, and the 21st cruise of the R. V. Kurchatov, 1964-1967. These are reported to have been the first by Russian vessels in this region embracing substantial geophysical investigations. Igneous petrology is tackled in six chapters. Those by Udintsev and Dmitriev (the ultrabasics of the sea floor) and by Baturin and Rozanova (ore mineralization) attract especial topical interest. Udintsev and Dmitriev tentatively conclude that sea water plays no role in the widespread serpentinization of the rift zone ultrabasics; serpentinization is a result primarily of outgassing of the mantle. These authors reject the notions that serpentinization is responsible for the formation of the ocean ridges, and that the ultrabasics are the residue of basalt fractionation. The contribution by Baturin and Rozanova (“Ore Mineralization in the Rift Zone of the Indian Ocean”) is limited to the description and discussion of two specimens. The first is a granulite dredged at 5” 23’ S, 68” 35’ E, the second a metamorphic subjected to multiple hydrothermal alteration, dredged at the same locality. The chapter by Bayuk and 12 co-authors provides a useful summary of the physical properties of the rift zone basalts, those of oceanic islands and continents, and rift-zone peridotites. Useful values are reported of the following: P and S velocities at various pressures; velocity anisotropy; activation energy; thermal
and electrical conductivity; specific heat and its temperature dependence; dielectric constant; demagnetizing field; saturation field; remanent saturation magnetization; Q factor, and Curie point. Two chapters (by Bezrukov et al. and by Kogan and Udintsev) provide a summary of the bottom sediments, their structure, and the climatic and structural controls operative in this large region. Attention is concentrated upon the peculiarities of sedimentation processes in the rift itself. Geophysical investigations included the use of bottom-planted geophones and continuous gravity profiles. Seismological studies utilized both refraction and lo-channel reflection techniques. Records were subjected to various sorts of signal enhancement, includign deconvolution. The maximum recording range for refraction was 40-50 km. Refraction stations found a “Moho” velocity of 7.2 km/set beneath the rift axis. Additionally, a layer having a velocity of 9 km/set appears to be up-arched beneath the central part of the ridge. Bottom-plant detectors were of the buoyattached rather than the internally recording, pop-up variety. Seismicity was found to be intense and concentrated principally in the rift axis (apparently in contrast to the transforms). A small number of heat flow stations was run and corrected for thermal disturbances. Small-scale, intense variations in the heat flow are attributed to petrologic inhomogeneities and faulting rather than to sea-floor convective circulation of the type shown recently by Lister (1974) to be important. The curve summarizing heat flow versus water depth (like all such, suffering from insufficient sample density) shows two maxima. The first, reaching 3 heat flow units, is located at about 40 km from the rift axis, the second at 190 km. The mean heat flow for the Indian Ocean floor deduced by these authors, taking account also of numerous measurements by Scripps expeditions and others, is 1.20 heat flow units, approximately equivalent to the world mean. The magnetic studies by “Vityaz” and “Kurchatov” were limited in area, and serve principally to confirm the magnetic pattern of the sea floor previously reported many times. The anomalies are not identified in terms of their Heirtzler numeration, and long-distance correlation is eschewed. Gravimetric profiles establish the existence of some important features, such as a -60 milligals free-air anomaly at the foot of the Arabian-Indian section of the ridge. The gravity studies serve to confirm a structural asymmetry between the eastern and western ridge flanks, shown also by the seismic profiles. The morphology of the Indian Ocean basin is well 144
Copyright All rights
0 1977 by the University of Washington. of reproduction in any form reserved.
ISSN 0033-5894
BOOK REVIEWS described. The deepest parts of the rift gorges are entirely isolated. leading to a characteristic hydrologic regime and bottom fauna. Those using this volume for the first time are advised to commence by reading Chapter 19. This presents an excellent summary by Dmitriev and others of oceanic crustal models as seen in the early seventies, and elucidates the research philosophy underlying the investigations which are reported in detail earlier. Their summary, furthermore, pinpoints, from an uncommitted viewpoint, many of the problems faced in plate tectonics. Russian investigators attach importance to the sharp distinction they believe they can perceive between the broad, rift-generated ridge flanks, and the adjoining oceanic plate. One is reminded that the researches of Beck and Lehner (1974) point to unexplored factors of similar importance relating the structure of the South Atlantic sea floor to the African flood basalts. A worthwhile attempt is made in this volume not to force fit data into preconceived notions as to what well-behaved lithosphere plates are expected to do, and to be careful to allow the facts to speak. Perhaps for this reason, little attempt is made to synthesize a system accounting for the firstorder elements of sea-floor architecture. In their summary, Dmitriev et al. propose the existence of diapir-like structures rooted in the lower mantle, surmounted by extrusion zones within which differentiate rises to the upper mantle-to this reviewer a concept reminiscent of mantle plumes. The majority opinion seems to incline to the view that sea-floor spreading is associated with primary, one-way, mantle differentiation processes, as distinct from circulatory convection of thermal origin. The researches represented in this volume are characterized by competent, imaginative direction and interpretation: but seem to have been handicapped at every turn by insufficient and ineffective hardware. Granted that instrumentation has advanced enormously in the last decade, it is noteworthy that the accuracy of the floating gravimeter employed, as measured at profile intersections, is k11.5 mgl; that the ship’s radio had to be shut down during magnetometer operations due to inadequate shielding; and that in the absence of a power winch, there was time to deploy only 10 of 20 reflection detector groups. One views less sympathetically the introduction of such terms as “georiftogenals.” Perhaps these sound less painful in Russian. “Rift Zones” is a mine of useful data and shared experience. Not the least useful part of this volume is its extensive listing of Russian topical literature. Generous reference is made to investigations conducted “in the West.” The translation is polished and reads easily.
REFERENCES Lister. C. R. B. (1974). Water percolation in the oceanic crust. EOS, Transactions of the American Geophysics
Union
55,
740-742.
145
Beck, R. H., and Lehner, P. (1974). Oceans, new frontier in exploration, Bulletin of the American Association
of Petroleum
Geologists
58, 376-395.
R. C. BOSTROM Department of Geological Sciences University of Washington Seattle. Washington 98195
Playas
and
Dried
Lakes:
Occurrence
and
Develop-
menf. James T. Neal, Ed. Dowden, Hutchinson, & Ross, Stroudsburg, Pennsylvania, 411 pp.. 1975, $28.00.
The book “Playas and Dried Lakes” is the 20th in a series entitled Benchmark Papers in Geology (R. W. Fairbridge, Series Editor). In the Preface, Fairbridge explains that the series is intended to provide a means of gathering into single volumes the critical material needed to reconstruct the fundamentals of the chosen topic. This book achieves that purpose. The editor of this volume. James T. Neal, Professor at the U. S. Air Force Academy at the time the volume was prepared, has selected 29 papers that deal with one or more aspects of playas and dried lakes. Twenty-two of these are presented in their entirety, and seven represent selected portions of larger works. One was translated from Russian. All are reproduced photographically from the original publication; the quality is generally good, although the wide variety in resulting type sizes may annoy some. Most of the line diagrams and many of the photographs are quite clear, but some photographs (especially in articles 23 and 25) do not compare favorably with those in the original papers. In the five-page Introduction, Neal discusses playa nomenclature, relevant climatic factors, the origins of closed basins, the required hydrology, the importance of playas to man, and the basis for grouping the selected papers into five categories: (I) past climates and antecedent lakes in playa basins: (2) hydrologic variations and implications; (3) variations in playa types, origins, and regions; (4) processes and surface features; and (5) investigative methods. Preceding the papers in each category are three to eight pages of comments by the editor designed to summarize the contents of the selected papers. add supplemental data and ideas from other sources, permit citation of additional references, and note the professional background of the authors. The papers reproduced have the following authorship. Group I: R. B. Morrison (1968), R. B. Morrison (1966). G. I. Smith (1962). and G. H. Dury (1973). Group 2: U[I]. C. Russell (1885), D. C. Hahl. M. T. Wilson, and R. H. Langford (1965). W. B. Langbein (1961). C. T. Snyder(1962), J. H. Feth (1966), and 1. J. Winograd (1962). Group 3: G. D. Thompson (1929). C. C. Reeves. Jr. (1966), C. Boocock and J. J. van Straten (1962). R. F. Flint and G. Bond (1968). D. B. Krinsley (1970). C. R. Twidale (1972). H. T. U. Smith
RESEARCH
7, I&-
147 (1977)
BOOK REVIEWS Rift Zones of the World Ocean. A. P. Vinogradov and G. B. Udintsev, Eds. Halsted Press, New York, 503 p., 1975, $55.00. According to the new global tectonics, each year more than 100 cubic kilometers of material is added to the floor of the world ocean at the zone of rifting. If a disparity, temporary but long in human terms, arises in the rate at which material is removed in subduction regions, what is the effect on sea level? Might it obscure the effects of deglaciation and isostatic rebound? What is the nature of the sediment found to be accumulating in certain sectors of the rift? What is the disposition of “pollution” added to ocean waters at the rift axis? If activity at the rift axis is any indication, processes of internal origin may play a larger role than expected in the geology of the recent past. The title of this densely packed, valuable volume appearing under the auspices of Vinogradov and Udintsev is a misnomer. Only three chapters treat of the oceanic rift system as a whole. These serve to relate its essential contents, an account of Soviet investigations of the floor of the Indian Ocean, to the world rift system. Nineteen chapters in all recount the coverage and results obtained in the Indian Ocean during the 36th and 41st cruises of the R. V. Vityaz, and the 21st cruise of the R. V. Kurchatov, 1964-1967. These are reported to have been the first by Russian vessels in this region embracing substantial geophysical investigations. Igneous petrology is tackled in six chapters. Those by Udintsev and Dmitriev (the ultrabasics of the sea floor) and by Baturin and Rozanova (ore mineralization) attract especial topical interest. Udintsev and Dmitriev tentatively conclude that sea water plays no role in the widespread serpentinization of the rift zone ultrabasics; serpentinization is a result primarily of outgassing of the mantle. These authors reject the notions that serpentinization is responsible for the formation of the ocean ridges, and that the ultrabasics are the residue of basalt fractionation. The contribution by Baturin and Rozanova (“Ore Mineralization in the Rift Zone of the Indian Ocean”) is limited to the description and discussion of two specimens. The first is a granulite dredged at 5” 23’ S, 68” 35’ E, the second a metamorphic subjected to multiple hydrothermal alteration, dredged at the same locality. The chapter by Bayuk and 12 co-authors provides a useful summary of the physical properties of the rift zone basalts, those of oceanic islands and continents, and rift-zone peridotites. Useful values are reported of the following: P and S velocities at various pressures; velocity anisotropy; activation energy; thermal
and electrical conductivity; specific heat and its temperature dependence; dielectric constant; demagnetizing field; saturation field; remanent saturation magnetization; Q factor, and Curie point. Two chapters (by Bezrukov et al. and by Kogan and Udintsev) provide a summary of the bottom sediments, their structure, and the climatic and structural controls operative in this large region. Attention is concentrated upon the peculiarities of sedimentation processes in the rift itself. Geophysical investigations included the use of bottom-planted geophones and continuous gravity profiles. Seismological studies utilized both refraction and lo-channel reflection techniques. Records were subjected to various sorts of signal enhancement, includign deconvolution. The maximum recording range for refraction was 40-50 km. Refraction stations found a “Moho” velocity of 7.2 km/set beneath the rift axis. Additionally, a layer having a velocity of 9 km/set appears to be up-arched beneath the central part of the ridge. Bottom-plant detectors were of the buoyattached rather than the internally recording, pop-up variety. Seismicity was found to be intense and concentrated principally in the rift axis (apparently in contrast to the transforms). A small number of heat flow stations was run and corrected for thermal disturbances. Small-scale, intense variations in the heat flow are attributed to petrologic inhomogeneities and faulting rather than to sea-floor convective circulation of the type shown recently by Lister (1974) to be important. The curve summarizing heat flow versus water depth (like all such, suffering from insufficient sample density) shows two maxima. The first, reaching 3 heat flow units, is located at about 40 km from the rift axis, the second at 190 km. The mean heat flow for the Indian Ocean floor deduced by these authors, taking account also of numerous measurements by Scripps expeditions and others, is 1.20 heat flow units, approximately equivalent to the world mean. The magnetic studies by “Vityaz” and “Kurchatov” were limited in area, and serve principally to confirm the magnetic pattern of the sea floor previously reported many times. The anomalies are not identified in terms of their Heirtzler numeration, and long-distance correlation is eschewed. Gravimetric profiles establish the existence of some important features, such as a -60 milligals free-air anomaly at the foot of the Arabian-Indian section of the ridge. The gravity studies serve to confirm a structural asymmetry between the eastern and western ridge flanks, shown also by the seismic profiles. The morphology of the Indian Ocean basin is well 144
Copyright All rights
0 1977 by the University of Washington. of reproduction in any form reserved.
ISSN 0033-5894
BOOK REVIEWS described. The deepest parts of the rift gorges are entirely isolated. leading to a characteristic hydrologic regime and bottom fauna. Those using this volume for the first time are advised to commence by reading Chapter 19. This presents an excellent summary by Dmitriev and others of oceanic crustal models as seen in the early seventies, and elucidates the research philosophy underlying the investigations which are reported in detail earlier. Their summary, furthermore, pinpoints, from an uncommitted viewpoint, many of the problems faced in plate tectonics. Russian investigators attach importance to the sharp distinction they believe they can perceive between the broad, rift-generated ridge flanks, and the adjoining oceanic plate. One is reminded that the researches of Beck and Lehner (1974) point to unexplored factors of similar importance relating the structure of the South Atlantic sea floor to the African flood basalts. A worthwhile attempt is made in this volume not to force fit data into preconceived notions as to what well-behaved lithosphere plates are expected to do, and to be careful to allow the facts to speak. Perhaps for this reason, little attempt is made to synthesize a system accounting for the firstorder elements of sea-floor architecture. In their summary, Dmitriev et al. propose the existence of diapir-like structures rooted in the lower mantle, surmounted by extrusion zones within which differentiate rises to the upper mantle-to this reviewer a concept reminiscent of mantle plumes. The majority opinion seems to incline to the view that sea-floor spreading is associated with primary, one-way, mantle differentiation processes, as distinct from circulatory convection of thermal origin. The researches represented in this volume are characterized by competent, imaginative direction and interpretation: but seem to have been handicapped at every turn by insufficient and ineffective hardware. Granted that instrumentation has advanced enormously in the last decade, it is noteworthy that the accuracy of the floating gravimeter employed, as measured at profile intersections, is k11.5 mgl; that the ship’s radio had to be shut down during magnetometer operations due to inadequate shielding; and that in the absence of a power winch, there was time to deploy only 10 of 20 reflection detector groups. One views less sympathetically the introduction of such terms as “georiftogenals.” Perhaps these sound less painful in Russian. “Rift Zones” is a mine of useful data and shared experience. Not the least useful part of this volume is its extensive listing of Russian topical literature. Generous reference is made to investigations conducted “in the West.” The translation is polished and reads easily.
REFERENCES Lister. C. R. B. (1974). Water percolation in the oceanic crust. EOS, Transactions of the American Geophysics
Union
55,
740-742.
145
Beck, R. H., and Lehner, P. (1974). Oceans, new frontier in exploration, Bulletin of the American Association
of Petroleum
Geologists
58, 376-395.
R. C. BOSTROM Department of Geological Sciences University of Washington Seattle. Washington 98195
Playas
and
Dried
Lakes:
Occurrence
and
Develop-
menf. James T. Neal, Ed. Dowden, Hutchinson, & Ross, Stroudsburg, Pennsylvania, 411 pp.. 1975, $28.00.
The book “Playas and Dried Lakes” is the 20th in a series entitled Benchmark Papers in Geology (R. W. Fairbridge, Series Editor). In the Preface, Fairbridge explains that the series is intended to provide a means of gathering into single volumes the critical material needed to reconstruct the fundamentals of the chosen topic. This book achieves that purpose. The editor of this volume. James T. Neal, Professor at the U. S. Air Force Academy at the time the volume was prepared, has selected 29 papers that deal with one or more aspects of playas and dried lakes. Twenty-two of these are presented in their entirety, and seven represent selected portions of larger works. One was translated from Russian. All are reproduced photographically from the original publication; the quality is generally good, although the wide variety in resulting type sizes may annoy some. Most of the line diagrams and many of the photographs are quite clear, but some photographs (especially in articles 23 and 25) do not compare favorably with those in the original papers. In the five-page Introduction, Neal discusses playa nomenclature, relevant climatic factors, the origins of closed basins, the required hydrology, the importance of playas to man, and the basis for grouping the selected papers into five categories: (I) past climates and antecedent lakes in playa basins: (2) hydrologic variations and implications; (3) variations in playa types, origins, and regions; (4) processes and surface features; and (5) investigative methods. Preceding the papers in each category are three to eight pages of comments by the editor designed to summarize the contents of the selected papers. add supplemental data and ideas from other sources, permit citation of additional references, and note the professional background of the authors. The papers reproduced have the following authorship. Group I: R. B. Morrison (1968), R. B. Morrison (1966). G. I. Smith (1962). and G. H. Dury (1973). Group 2: U[I]. C. Russell (1885), D. C. Hahl. M. T. Wilson, and R. H. Langford (1965). W. B. Langbein (1961). C. T. Snyder(1962), J. H. Feth (1966), and 1. J. Winograd (1962). Group 3: G. D. Thompson (1929). C. C. Reeves. Jr. (1966), C. Boocock and J. J. van Straten (1962). R. F. Flint and G. Bond (1968). D. B. Krinsley (1970). C. R. Twidale (1972). H. T. U. Smith