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Precambrian Ophiolites and Related Rocks
Precambrian Research 138 (2005) 181–182
Book review
T.M. Kusky (Ed.), Precambrian Ophiolites and Related Rocks. in: Developments in Precambrian Geology 13, Elsevier, Amsterdam, 2004, ISBN 0444509232, 748 pp. This is the fourth major book on ophiolites to be published in the last 4–5 years. You might think that by now most has been said on the subject, but this volume edited by Tim Kusky presents entirely new information on Precambrian ophiolites and a very useful and important overview about the early evolution of the earth. The book contains 21 papers of new and synthesized information on ophiolites that range in age from early Archaean to Neoproterozoic, plus two thoughtprovoking reviews by Kusky. The first is a 34-page, introduction and review of the main problems and processes derived from previous studies of Precambrian ophiolites and a synopsis of the volume, and the second is an 11-page epilogue entitled ‘What if anything have we learned about Precambrian ophiolites and early earth processes?’ The book contains: six papers on ‘Proterozoic ophiolites’, nine on ‘Archaean ophiolites’, three on ‘Models for the evolution of oceanic crust with time’, and three on ‘Analogs to Precambrian ophiolites’ – Northern Philippine (J. Encarnacion), Resurrection in Alaska (T.M. Kusky et al.) and ‘ophirags’ (ophiolite fragments) in the Altaids of eastern Asia (A.M.C. Seng¨or and B.A. Natal’in). The following are important highlights: An important development is the recognition of a new class of ophiolites, ‘transitional ophiolites’, based on the Cretaceous magma-poor rifted West Iberian continental margin (Cornen et al., 1999; Whitmarsh et al., 2001). The 2.1-1.95 Ga Jormua ophiolite in Finland with its well-preserved basaltic sheeted dyke complex
0301-9268/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.precamres.2005.06.001
has long been recognized as one of the oldest ophiolites in the world. As Peltonen and Kontinen describe in this volume, it consists of Archaean subcontinental mantle exposed on the seafloor during early rifting and detachment, intruded by dykes, and overlain directly by tholeiitic (EMORB) pillow lavas and intruded by coeval dikes and gabbros; the evidence suggests it formed within an ocean-continental transition zone. Another ‘modern’ example (Kusky, introduction) is at Tihama Asir, Saudi Arabian, where a 5–10 Ma old transitional ophiolite has a dyke complex overlying layered gabbro, which in turn overlies continental crust. These chronologies and modern analogues explain many of the relations of the previously disputed Archaean ocean floor relicts in the Slave Province of NW Canada, which lie upon mylonitic granitic crust, as recorded by Corcoran et al., as also those in the Belingwe belt in Zimbabwe (A. Hoffman and T. Kusky). It is this sort of conceptual advance based on detailed new data and modern analogue that is most important for understanding Precambrian ophiolites. When published in 2001 by Kusky et al. the 2.5 Ga Dongwanzi ophiolite in Northern China proved controversial. In this book there are four multi-author papers on this ophiolite and the neighbouring Zinhua ophiolitic melange that present much new data on dykes, lavas, geochemistry, chromite, geochronology and microstructures. Within a 130 × 20 km2 area of the North China craton the Zinhua belt of biotite gneisses contains over 1000 lenses of gabbro, pillow lava, sheeted dykes, harzburgite, and podiform chromite-bearing dunite. This is very reminiscent of the relations in West Greenland, where there are not only well-preserved intact layers up to 2 km thick of anorthosite, leucogabbro, gabbro, and ultramafic rocks
182
Book review / Precambrian Research 138 (2005) 181–182
belonging to the 3.0 Ga Fiskenaesset Complex, but also millions of lenses of these rocks within tonalitic biotite gneisses. The lenses were created when the protoliths of the gneisses were emplaced as sheet intrusions into the layered complex. A similar history of events seems to have taken place in northern China, but much fieldwork is yet required to map out and document the relations and lithologies. An increasing number of Precambrian ophiolites are being found that contain calc-alkaline rocks and/or calc-alkaline geochemical signatures. Since many Phanerozoic ophiolites like Troodos in Cyprus and Semail in Oman have some calc-alkaline and suprasubduction characteristics, that may not be surprising. For example, the 1.73 Ga Payson ophiolite in Arizona contains not only splendid basaltic sheeted dykes, but also, albeit rare, tonalitic/dacitic lavas and dykes (J.C. Dann). There are two papers on the 870-695 Ma ophiolites in the Arabian-Nubian shield (R.J. Stern et al.; P.R. Johnson et al.), the mineral/lava compositions and Cr# of which point to forearc suprasubduction settings. A similar setting is suggested for the 808 Ma Wadi Onib ophiolite in Sudan (I.M. Hussen et al.). The 596 Ma Adardagh Tes-Chem ophiolite in Tuva, Siberia has geochemical data that reveal an island arc and back-arc origin (J. A. Pf˚ander and A. Kr¨oner). Boninites provide further evidence of a suprasubduction zone environment, as well documented by I.S. Puchtel in the 3.0 Ga Olondo ophiolitic greenstone belt in the Aldan Shield, Siberia (tholeiitic and komatiitic basalts, gabbro sills, and dunites and peridotites derived from a boninitic melt), and by A.A. Shchipansky et al. in the 2.8 Ga ophiolite in the Karelian greenstone belt in the NE Baltic Shield of Russia that contains boninitic and tholeiitic lavas, sheeted dykes and gabbro that formed by subduction-related processes. Komatiites in the Barberton belt formed from fore-arc magmatism (S.W. Parman and T.L. Grove). Particularly in
Archaean belts it is obviously important to distinguish ophiolitic rocks with arc-type lithologies and chemistry from genuine island arcs; A. Polat and R. Kerrich have a detailed, excellent paper on ‘Precambrian arc associations: boninites, adakites, magnesian andesites, and Nb-enriched basalts’. Finally, we can ask the question ‘do Archaean greenstone belts contain fragments of ophiolites’; that is answered positively by M.J. de Wit. I have learnt a great deal from this book, and highly recommend it to all those interested in Precambrian ophiolites and associated rocks, and to relevant libraries. It is full of new and synthesized data, is upto-date on conceptual advances, and is well presented with many figures in colour. It will certainly be a major invaluable reference in the future. But pity about the price! Hardbound, ISBN: 0-444-50923-2 Price: GBP 124, USD 198, EUR 180. The book is available in Europe, Middle East and Africa from the Elsevier Customer Support Department, Linacre House, Jordan hill, Oxford OX2 8DP, UK, or in the USA/Canada from Elsevier, Customer Service Department, 11830 Westline Industrial Drive, St. Louis, MP 63146, U.S.A.
References Cornen, G., Girardeau, J., Monnier, C., 1999. Basalts, underplated gabbros and pyroxenites record the rifting process of the West Iberian margin. Mineral. Petrol. 67, 111–142. Whitmarsh, R.B., Manatschai, G., Minshull, T.A., 2001. Evolution of magma-poor continental margins from rifting to seafloor spreading. Nat. 413, 150–154.
Brian Windley Department of Geology, University of Leicester Leicester LE1 7RH, UK
Book review
T.M. Kusky (Ed.), Precambrian Ophiolites and Related Rocks. in: Developments in Precambrian Geology 13, Elsevier, Amsterdam, 2004, ISBN 0444509232, 748 pp. This is the fourth major book on ophiolites to be published in the last 4–5 years. You might think that by now most has been said on the subject, but this volume edited by Tim Kusky presents entirely new information on Precambrian ophiolites and a very useful and important overview about the early evolution of the earth. The book contains 21 papers of new and synthesized information on ophiolites that range in age from early Archaean to Neoproterozoic, plus two thoughtprovoking reviews by Kusky. The first is a 34-page, introduction and review of the main problems and processes derived from previous studies of Precambrian ophiolites and a synopsis of the volume, and the second is an 11-page epilogue entitled ‘What if anything have we learned about Precambrian ophiolites and early earth processes?’ The book contains: six papers on ‘Proterozoic ophiolites’, nine on ‘Archaean ophiolites’, three on ‘Models for the evolution of oceanic crust with time’, and three on ‘Analogs to Precambrian ophiolites’ – Northern Philippine (J. Encarnacion), Resurrection in Alaska (T.M. Kusky et al.) and ‘ophirags’ (ophiolite fragments) in the Altaids of eastern Asia (A.M.C. Seng¨or and B.A. Natal’in). The following are important highlights: An important development is the recognition of a new class of ophiolites, ‘transitional ophiolites’, based on the Cretaceous magma-poor rifted West Iberian continental margin (Cornen et al., 1999; Whitmarsh et al., 2001). The 2.1-1.95 Ga Jormua ophiolite in Finland with its well-preserved basaltic sheeted dyke complex
0301-9268/$ – see front matter © 2005 Published by Elsevier B.V. doi:10.1016/j.precamres.2005.06.001
has long been recognized as one of the oldest ophiolites in the world. As Peltonen and Kontinen describe in this volume, it consists of Archaean subcontinental mantle exposed on the seafloor during early rifting and detachment, intruded by dykes, and overlain directly by tholeiitic (EMORB) pillow lavas and intruded by coeval dikes and gabbros; the evidence suggests it formed within an ocean-continental transition zone. Another ‘modern’ example (Kusky, introduction) is at Tihama Asir, Saudi Arabian, where a 5–10 Ma old transitional ophiolite has a dyke complex overlying layered gabbro, which in turn overlies continental crust. These chronologies and modern analogues explain many of the relations of the previously disputed Archaean ocean floor relicts in the Slave Province of NW Canada, which lie upon mylonitic granitic crust, as recorded by Corcoran et al., as also those in the Belingwe belt in Zimbabwe (A. Hoffman and T. Kusky). It is this sort of conceptual advance based on detailed new data and modern analogue that is most important for understanding Precambrian ophiolites. When published in 2001 by Kusky et al. the 2.5 Ga Dongwanzi ophiolite in Northern China proved controversial. In this book there are four multi-author papers on this ophiolite and the neighbouring Zinhua ophiolitic melange that present much new data on dykes, lavas, geochemistry, chromite, geochronology and microstructures. Within a 130 × 20 km2 area of the North China craton the Zinhua belt of biotite gneisses contains over 1000 lenses of gabbro, pillow lava, sheeted dykes, harzburgite, and podiform chromite-bearing dunite. This is very reminiscent of the relations in West Greenland, where there are not only well-preserved intact layers up to 2 km thick of anorthosite, leucogabbro, gabbro, and ultramafic rocks
182
Book review / Precambrian Research 138 (2005) 181–182
belonging to the 3.0 Ga Fiskenaesset Complex, but also millions of lenses of these rocks within tonalitic biotite gneisses. The lenses were created when the protoliths of the gneisses were emplaced as sheet intrusions into the layered complex. A similar history of events seems to have taken place in northern China, but much fieldwork is yet required to map out and document the relations and lithologies. An increasing number of Precambrian ophiolites are being found that contain calc-alkaline rocks and/or calc-alkaline geochemical signatures. Since many Phanerozoic ophiolites like Troodos in Cyprus and Semail in Oman have some calc-alkaline and suprasubduction characteristics, that may not be surprising. For example, the 1.73 Ga Payson ophiolite in Arizona contains not only splendid basaltic sheeted dykes, but also, albeit rare, tonalitic/dacitic lavas and dykes (J.C. Dann). There are two papers on the 870-695 Ma ophiolites in the Arabian-Nubian shield (R.J. Stern et al.; P.R. Johnson et al.), the mineral/lava compositions and Cr# of which point to forearc suprasubduction settings. A similar setting is suggested for the 808 Ma Wadi Onib ophiolite in Sudan (I.M. Hussen et al.). The 596 Ma Adardagh Tes-Chem ophiolite in Tuva, Siberia has geochemical data that reveal an island arc and back-arc origin (J. A. Pf˚ander and A. Kr¨oner). Boninites provide further evidence of a suprasubduction zone environment, as well documented by I.S. Puchtel in the 3.0 Ga Olondo ophiolitic greenstone belt in the Aldan Shield, Siberia (tholeiitic and komatiitic basalts, gabbro sills, and dunites and peridotites derived from a boninitic melt), and by A.A. Shchipansky et al. in the 2.8 Ga ophiolite in the Karelian greenstone belt in the NE Baltic Shield of Russia that contains boninitic and tholeiitic lavas, sheeted dykes and gabbro that formed by subduction-related processes. Komatiites in the Barberton belt formed from fore-arc magmatism (S.W. Parman and T.L. Grove). Particularly in
Archaean belts it is obviously important to distinguish ophiolitic rocks with arc-type lithologies and chemistry from genuine island arcs; A. Polat and R. Kerrich have a detailed, excellent paper on ‘Precambrian arc associations: boninites, adakites, magnesian andesites, and Nb-enriched basalts’. Finally, we can ask the question ‘do Archaean greenstone belts contain fragments of ophiolites’; that is answered positively by M.J. de Wit. I have learnt a great deal from this book, and highly recommend it to all those interested in Precambrian ophiolites and associated rocks, and to relevant libraries. It is full of new and synthesized data, is upto-date on conceptual advances, and is well presented with many figures in colour. It will certainly be a major invaluable reference in the future. But pity about the price! Hardbound, ISBN: 0-444-50923-2 Price: GBP 124, USD 198, EUR 180. The book is available in Europe, Middle East and Africa from the Elsevier Customer Support Department, Linacre House, Jordan hill, Oxford OX2 8DP, UK, or in the USA/Canada from Elsevier, Customer Service Department, 11830 Westline Industrial Drive, St. Louis, MP 63146, U.S.A.
References Cornen, G., Girardeau, J., Monnier, C., 1999. Basalts, underplated gabbros and pyroxenites record the rifting process of the West Iberian margin. Mineral. Petrol. 67, 111–142. Whitmarsh, R.B., Manatschai, G., Minshull, T.A., 2001. Evolution of magma-poor continental margins from rifting to seafloor spreading. Nat. 413, 150–154.
Brian Windley Department of Geology, University of Leicester Leicester LE1 7RH, UK