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The geochronology and evolution of Africa
Chemical Geology (Isotope Geoscience Section), 62 (1985) 397-398 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands
397
Book Review The Geochronology
and Evolution
of Africa.
L. Cahen, N.J. Snelling, J. Delhal and J.R. Vail (with the collaboration of M. Bonhomme and D. Ledent). Clarendon Press, Oxford, 1984, 512 pp., UK 660.00. This volume contains a wealth of information on the geochronology and geological evolution of Africa, and will be extremely useful to a broad spectrum of earth scientists. The subject matter is clearly presented and logically arranged on a geographical basis; there are a large number of carefully compiled tables and maps, and the text is supported by an extensive (50 page) referencelist as well as a subject index. I have noted only a few typographical errors, no mean achievement bearing in mind that many of the place names are African in origin. It would hardly be possible for a reviewer to check the accuracy of the enormous volume of numerical data presented, but I have noted no errors in the areaswith which I am familiar. It is commendable that the authors have gone back to the original sources of the analytical data, and have included sourcesof information (such astheses) that are not readily accessible. Chapter I (Introduction) provides a concise summary of recent developments in geochronology and methodology, but I do feel that in a book of this length there would have been an advantage for the non-specialist reader in also summarising the principles of the subject even though much of this material is available elsewhere. Of particular value in this chapter is the section on computing methods, and adding immeasurably to the value of the book as a whole is the fact that all data have been recalculated on the basisof modern decay constants and that where possible original regression analyses have been recalculated using a uniform and logical approach. Accordingly, readers can safely make comparisons between sets of data of particular interest to them, whereasin the past such
comparisons have often been marred by failure to take account of differences between decay constants used, etc. A useful distinction is made between “apparent”, “conventional” and “adopted” ages. The following twenty chapters are devoted to consideration of specific regions, divided on a broad regional basis but with geological characteristics such as mobile belts, cratonic provinces, etc., providing the main basis for subdivision. Each chapter has a concise Introducton and most end ~with a Synopsis. A valuable feature is that in some casesthe conclusions or interpretations of original authors are criticised, in a constructive manner, but always with a clear distinction being made between the views of the present and original authors. I am most familiar with the data for southern Africa, and consider the treatment to be sound and well balanced. It is unfortunate that the appearance of this volume so closely precededthe publication of much new data by workers involved in the South African Geodynamics Programme. Such coincidences are probably inevitable, but the result is that for southern Africa at least the new insights obtained from the presently available much larger data baseare not considered. Particular instances are the Limpop and Namaqua Mobile Belts, and the Karoo volcanics, and the attention of readers could perhaps have been drawn to Special Publications 8-13 of the Geological Society of South Africa in which much of the new information is published. The final two chapters review and discuss the tectono-thermal history, and the evolution of Africa. In both instancesit is my view that the discussion of initial isotope ratios (both Sr and Pb) would have much enhanced the discussion. In the Preface the Authors state that they have chosen not to do so because much of the evidence is of relatively poor precision and is likely to be superseded by modem high-precision studies now under way. The same argument could equally be
398
applied to many of the age determinations! Despite these minor criticisms this book is very well produced and should prove very use-
ful, mainly as a reference body of earth scientists.
source, to a large
HUGH ALLSOPP (Johannesburg)
Announcement SIXTH INTERNATIONAL
CONFERENCE ON GEOCHBONOLOGY, COS~HRONO~GY AND ISOTOPE GEOLOGY Cambxidge,U.K., June 3oJuly 4,1986
Sponsors: I.U.G.S. Subcommittee on Geochronology, International Association of Geochemistry and Cosmochemlstry, International Association of Volcanology and Chemistry of the Earth’s Interior (I.U.G.G), Geochemlcal Society, European Association of Geochemimstry, Royal Society of London. Further information can be obtained from: Organizing Committee Sixth International Conference Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ, U.K.
Erratum K-K. Liu and S. Epstein, 1984. The hydrogen Isot. Geosci., 2: 335-350. Footnote
isotope fractionation
between kaolinite
and water.
on p. 335. The present address should read:
Institute of Earth Sciences, Academica Sinica, P.O. Box 23-59, Taipei, Taiwan 107, Republic of China.
397
Book Review The Geochronology
and Evolution
of Africa.
L. Cahen, N.J. Snelling, J. Delhal and J.R. Vail (with the collaboration of M. Bonhomme and D. Ledent). Clarendon Press, Oxford, 1984, 512 pp., UK 660.00. This volume contains a wealth of information on the geochronology and geological evolution of Africa, and will be extremely useful to a broad spectrum of earth scientists. The subject matter is clearly presented and logically arranged on a geographical basis; there are a large number of carefully compiled tables and maps, and the text is supported by an extensive (50 page) referencelist as well as a subject index. I have noted only a few typographical errors, no mean achievement bearing in mind that many of the place names are African in origin. It would hardly be possible for a reviewer to check the accuracy of the enormous volume of numerical data presented, but I have noted no errors in the areaswith which I am familiar. It is commendable that the authors have gone back to the original sources of the analytical data, and have included sourcesof information (such astheses) that are not readily accessible. Chapter I (Introduction) provides a concise summary of recent developments in geochronology and methodology, but I do feel that in a book of this length there would have been an advantage for the non-specialist reader in also summarising the principles of the subject even though much of this material is available elsewhere. Of particular value in this chapter is the section on computing methods, and adding immeasurably to the value of the book as a whole is the fact that all data have been recalculated on the basisof modern decay constants and that where possible original regression analyses have been recalculated using a uniform and logical approach. Accordingly, readers can safely make comparisons between sets of data of particular interest to them, whereasin the past such
comparisons have often been marred by failure to take account of differences between decay constants used, etc. A useful distinction is made between “apparent”, “conventional” and “adopted” ages. The following twenty chapters are devoted to consideration of specific regions, divided on a broad regional basis but with geological characteristics such as mobile belts, cratonic provinces, etc., providing the main basis for subdivision. Each chapter has a concise Introducton and most end ~with a Synopsis. A valuable feature is that in some casesthe conclusions or interpretations of original authors are criticised, in a constructive manner, but always with a clear distinction being made between the views of the present and original authors. I am most familiar with the data for southern Africa, and consider the treatment to be sound and well balanced. It is unfortunate that the appearance of this volume so closely precededthe publication of much new data by workers involved in the South African Geodynamics Programme. Such coincidences are probably inevitable, but the result is that for southern Africa at least the new insights obtained from the presently available much larger data baseare not considered. Particular instances are the Limpop and Namaqua Mobile Belts, and the Karoo volcanics, and the attention of readers could perhaps have been drawn to Special Publications 8-13 of the Geological Society of South Africa in which much of the new information is published. The final two chapters review and discuss the tectono-thermal history, and the evolution of Africa. In both instancesit is my view that the discussion of initial isotope ratios (both Sr and Pb) would have much enhanced the discussion. In the Preface the Authors state that they have chosen not to do so because much of the evidence is of relatively poor precision and is likely to be superseded by modem high-precision studies now under way. The same argument could equally be
398
applied to many of the age determinations! Despite these minor criticisms this book is very well produced and should prove very use-
ful, mainly as a reference body of earth scientists.
source, to a large
HUGH ALLSOPP (Johannesburg)
Announcement SIXTH INTERNATIONAL
CONFERENCE ON GEOCHBONOLOGY, COS~HRONO~GY AND ISOTOPE GEOLOGY Cambxidge,U.K., June 3oJuly 4,1986
Sponsors: I.U.G.S. Subcommittee on Geochronology, International Association of Geochemistry and Cosmochemlstry, International Association of Volcanology and Chemistry of the Earth’s Interior (I.U.G.G), Geochemlcal Society, European Association of Geochemimstry, Royal Society of London. Further information can be obtained from: Organizing Committee Sixth International Conference Department of Earth Sciences University of Cambridge Downing Street Cambridge CB2 3EQ, U.K.
Erratum K-K. Liu and S. Epstein, 1984. The hydrogen Isot. Geosci., 2: 335-350. Footnote
isotope fractionation
between kaolinite
and water.
on p. 335. The present address should read:
Institute of Earth Sciences, Academica Sinica, P.O. Box 23-59, Taipei, Taiwan 107, Republic of China.