Journal of Volcanology and Geothermal Research, 49 ( 1992 ) 385-391 385 Elsevier Science Publishers B.V., Amsterdam

Book Reviews

Mafic Dykes and Emplacement Mechanisms. Proceedings of the Second International Dyke Con- ference, Adelaide/South Australia, 12-16 September, 1990, edited by A.J. Parker, P.C. Rick- wood and D.H. Tucker, A.A. Balkema, Rotterdam, The Netherlands, 1990. Hardcover, x + 541 pp., ISBN 90-6191-1583, Dfl. 135.00.

There has been a renaissance of interest in dykes in the last ten years or so, particularly in their physical occurrence and the tectonic and mechanical controls on emplacement in the crust. It is fortunate that much of this work is summarized in this latest book and its prede- cessor Mafic Dyke Swarms, H.C. Halls and W.F. Fahrig (editors), 1987, A collection of papers based on the Proceedings of the First International Dyke Conference held at Erin- dale College, University of Toronto, Ontario, Canada, June 4-7, 1985 (Geol. Assoc. Canada Special Paper 34, 503 pp. ). The book under re- view is based on the contents of the Second In- ternational Dyke Conference. It was issued at the conference, the Editors having achieved the remarkable goal of obtaining manuscripts be- fore the conference took place. This policy may well have "watered down" some of the papers and I note that more complete versions of sev- eral of the papers in the book have appeared subsequently in journals. However, there is much to be said for making the proceedings volume available at the t ime of the conference.

Mafic Dykes and Emplacement Mecha- nisms contains forty-eight papers, the majority author-prepared, divided into four major sec- tions: Emplacement Mechanisms (9 papers): Geochemistry, Petrology, and Mineralisation ( 9 papers); Paleomagnetism ( 5 papers); and Crustal Tectonics (25 papers). The latter topic is subdivided into studies of "Gondwanan" dykes ( 16 papers) and "Laurasian" dykes (9 papers).

The large section on Gondwana contains pa-

pers (some very brief) mainly describing the occurrence of Proterozoic to Early Paleozoic dykes in Amazonia, Africa, India and Aus- tralia, although the Cape Peninsula (South. Af- rica) dolerite swarm may be Jurassic in age. Two articles deal with dykes associated with the c. 65-60 Ma Deccan Trap volcanism in India, but direct relationships with the major lava outpourings are uncertain in both cases. Most of the papers give a broad picture, described from a local perspective, and include informa- tion on tectonic setting, major and trace ele- ment geochemistry and petrography, and geo- chronology; new isotopic data are sparse. A few of these studies also address aspects of the em- placement of the mafic intrusions.

The Laurasian section contains a mixed bunch of studies from Precambrian terranes of North America (Avalon), Greenland, Scot- land, and Siberia, together with a study of mafic enclaves and dykes in Cretaceous grani- toids in California, one paper on a Columbia River flood basalt feeder dyke, and one on a Middle Palaeozoic rift in Siberia. The ap- proach varies from regional structural studies to detailed field and petrographic studies on the scale of ten 's of metres. It is difficult to present a coherent review of these diverse articles as they vary so much in their alms and style of research.

The collection of papers on Emplacement Mechanisms is arguably the strongest part of the book. Again the articles cover a wide range of topics. Some get down to the basics and dis- cuss useful nomenclature applicable to dykes.

0377-0273/92/$05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved.

386

Others discuss methods for determining prop- agation and flow directions from field and structural characteristics; a paper in a later sec- tion evaluates flow directions using anisotropy of magnetic susceptibility (AMS). Other pa- pers examine dyke segmentation in a fractured host and crystallisation features related to in- trusion at great depths. There are also papers on radial dyke swarms associated with a Pleis- tocene submarine volcano in Japan and on a composite dyke from the Grenville Province of the Canadian shield. Two important studies cover fluid-mechanical models of dyke em- placement, based on modelling and laboratory simulations, and dyke emplacement at spread- ing centers, based largely on studies in Iceland.

Of the nine papers covering Geochemistry, Petrology, and Mineralisation, three are con- cerned with the Archaean rocks of Western Australia. One reports on the oldest (2.7-2.8 Ga) alkaline metamorphosed lamprophyric ultramafic dykes yet recognised, from the Pil- bara Block, and another is a review of lampro- phyric intrusions in Western Australia. The third is about the relationships between sites of dyke injection and gold mineralisation; it appears that the dykes were later intruded along the same planes of weakness that were fol- lowed or caused by the mineralising event. A diagram showing aeromagnetic data from this study also provides the eye-catching cover of the book. Other papers in this section include an isotopic study of the petrogenesis of Proter- ozoic dykes in California and Arizona, a trace- element and isotopic study of Appalachian dykes that intruded Late Proterozoic crust and are thought to have a continental lithospheric source, and a paper that describes an at tempt to track down the source of the Grenville dyke swarm in Canada. This study uses the tectonic setting and geochemistry of the large swarm, which was injected into a failed arm of the Ia- petan rift. The two other contributions are a trace element investigation of dykes in north-

ern Brazil that are thought to be related to mantle plumes associated with the opening of the central Atlantic in the early Mesozoic, and a study of enriched MORB-like dykes from the Rooi Rand swarm in southern Africa that in- trude the eastern (late, c. 190 Ma) Karoo flood basalts. These dolerites have different eNa and ~Sr values than the basalts and are thought to be derived largely from asthenospheric sources. The final paper describes the relationship be- tween silicic magmatism (rapakivi granites) and mafic dykes in the Proterozoic of Finland, and brings to bear the full range of geochemi- cal data on the problem of petrogenesis.

In the short section on Paleomagnet~c stud- ies, there is one review paper on the paleo- magnetism and geochemistry of the great dyke swarms of the Canadian Shield and two papers concerning large swarms from the same re- gion. One deals with direction of flow derived by AMS, and shows that magma travelled in directions consistent with being derived at the apex of the fan-shaped swarms, while the other discusses the evolution of the impressive Ma- tachewan dyke swarm. The other contribu- tions are a look at Early Proterozoic layered in- trusions and associated dykes in northern Finland, aimed at determining polar wander paths for the Fennoscandian region, and a lo- cal study of uplift in the Jurassic of the Sydney Basin, New South Wales. The latter is an aborted at tempt to use paleomagnetism to de- termine paleotemperatures and amount of overburden.

Overall, this book is a mixed bag. It lacks a coherent theme, or themes, other than that given by the title, but it does bring to a wide audience, in a timely fashion, a great deal of valuable information, much of it from sources that are difficult of access. It is a well presented book; perhaps the only shortcoming is the lack of a subject index. Obviously, it will be a must for affectionados of dykes.

STEPHEN SELF ( H o n o l u l u , Hawa i i )