The Field Description of Igneous Rocks

Contents

The Geological Field Guide Series

Barnes, J.W. and Lisle, R.J. (2004) Basic Geological Mapping, 4th edn. ISBN: 978-0-470-84986-6, 5th edn publishing (2011). ISBN: 978-0-470-68634-8

Fry, N. (1991) The Field Description of Metamorphic Rocks. ISBN: 978-0-471-93221-5

McClay, K.R. (1991) The Mapping of Geological Structures. ISBN: 978-0-471-93243-7

Milsom, J. and Eriksen, A. (2010) Field Geophysics, 4th edn. ISBN: 978-0-470-74984-5

Tucker, M.E. (2011) Sedimentary Rocks in the Field, 4th edn. ISBN: 978-0-470-68916-5

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Library of Congress Cataloguing-in-Publication Data

Jerram, Dougal.

The field description of igneous rocks/Dougal Jerram, Nick Petford. – 2nd ed.

p. cm. – (Geological field guide)

Rev. ed. of: The field description of igneous rocks/R.S. Thorpe and G.C. Brown. Milton. Keynes [Buckinghamshire]: Open University Press; New York: Halsted, 1985.

Includes index.

ISBN 978-0-470-02236-8 (pbk.)

1. Igneous rocks – Identification. 2. Geology – Fieldwork. I. Petford, N. (Nick) II. Title. QE461.T45 2011

552^′.1 – dc22

2010034826

This book is dedicated to Bob Hunter, and his great contribution to our understanding of rock textures.

ACKNOWLEDGEMENTS

DJ would like to thank James Haythornthwaite and Tim Watton for their skillful help in drafting some of the diagrams. Lorraine Field, Richard Walker, James Haythornthwaite, Tim Watton, Jon Davidson, Graham Pearson, Nick Schofield, Robin Gill, Tony Philpotts, Sergio Rocchi, Scott Patterson and Bruce Marsh are thanked for providing photographs and other graphic materials and support. Additional discussions with Catherine Nelson, Clayton Grove, Sam Clark, Kirstie Wright and the vibrant student and postgraduate community at Durham University proved very helpful. Henry Emeleus and Jon Davidson are also thanked for their comments on earlier drafts of some chapters. In addition to our many friends and colleagues (thanks, you know who you are!) who have informed and enlightened us in the field NP would like to extend his gratitude to Mike Atherton, Wally Pitcher for the immortal ‘at the end of a long day in the field, a note saying white rock cuts black rock will do!’, Mr and Mrs A.P. Boyle, Donny Hutton, Colin Key, Ken McCaffrey, Stephano Pugliese, Mark Thomas and Eddie Bromhead. Fiona Woods and Rachael Ballard at Wiley are thanked for their help and patience. The final word goes to our long suffering families for putting up with all of this. Just wait until the next edition.

Illustrative matter appearing in this book was adapted from or inspired by the following sources to whom also grateful acknowledgement is made:

Figures 3.2, 3.11–3.14: R.V. Dietrich and B.J. Skinner, Rocks and Rock Minerals, Wiley (1979) A.G. Tindle; Figure 1.2: H. Williams and A.R. McBirney, Volcanology, Freeman, Cooper and Co. (1979); Figure 4.8: P. Lyle, J. Geol. Soc. Lon. 157 (2000); Figure 4.12 R.A.F. Cas and J.V. Wright, Volcanic Successions, Chapman & Hall (1988) & M. J. Branney, B. Bonnichsen, G. D. M. Andrews, B. Ellis, T. L. Barry and M. McCurry, Bull. Vol. 70(3) (2008); Figures 4.13, 4.17: G.A. Macdonald, Volcanoes, Prentice-Hall (1972); Figures 4.18, 4.19: R. Batiza and J.D.L. White In: Encyclopedia of Volcanoes, Academic Press (2000); Figure 5.3: K.H. Wohletz and M. F. Sheridan, Geol. Soc. Am. Spec. Paper 180 (1974); Figure 5.5: R.V. Fischer and H-U Schmincke, Pyroclastic Rocks, Springer-Verlag (1984); Figure 5.14: M.J. Branney and P.B. P Kokelaar, Geol. Soc. Memoir 72 (2002); Figure 5.16: R.S.J. Sparks, S. Self and G.P.L. Walker, Geology 1 (1973); Figures 5.15, 5.25, 8.14: R. Gill, Igneous Rocks and Processes, Wiley (2010); Figure 5.20: D. Dirk Vesperman and H-U. Schmincke, In: Encyclopedia of Volcanoes, Academic Press (2000); Figure 5.21: J.L. Smellie, In: Encyclopedia of Volcanoes, Academic Press (2000); Table 5.1: R. V. Fisher, Bull. Geol. Soc. Am. 72 (1961); Figure 6.12: M. G. Best and E.H. Christiansen, Igneous Petrology, Blackwell (2001); Figure 6.6: Hutton, Pet. Geosci., 15 (2009); Figure 7.1: F.H. Lahee, Field Geology, McGraw-Hill (1916); Figure 7.2: M.A. Bussell, W.S. Pitcher and P.A. Wilson, Can. J. Earth. Sci. 13 (1976); Figure 7.5: M. Haederle and M.P. Atherton, Tectonophysics 345 (2002); Figure 7.11: D.H.W. Hutton, 1988. Trans R. Soc. Ed.: Earth Sci. 91 (2000); Figure 7.13: N. Petford and M.P. Atherton, Tectonophysics 205 (1992); Figure 7.14: W.S. Pitcher and D.H.W. Hutton, Geol. Sur. of Ireland (2003); Figure 7.21: J.G. Arth, F. Barker, D.E. Peterman and I. Friedman, J. Petrol. 19 (1978); Figure 7.22: W.S. Pitcher, The Nature and Origin of Granite, Blackie Academic Professional (1993); Figures 8.8, 8.9: J.D. Winter, Pearson Education/Prentice Hall (2001); Figure 9.1: E. Hallot et al., J. of Volc. Geo. Res. 71,1996; Figure 9.4: S. Pugliese and N. Petford, Visual Geosci., 6 (2001); Figure 9.10: B. Barbarin, Schweizerische Mineralogische und Petrographische Mitteilungen, 69, (1989); Figure 10.3: R.H. Sillitoe, Geol. Ass. Canada Spec. Paper 14 (1976); Figure 10.9: M.O. Sarr and M. Manga, Geophys. Res. Lett. 26 (1999); Figure 10.8: D. Norton and R. Knapp, Amer J. Science 277 (1977); Figure 10.11: M. Thomas, PhD Thesis, Kingston University (2007).

PREFACE

Igneous rocks in the field present a bewildering array of lithiologies formed not just from cooling and crystallisation of intrusive material but also by sedimentation and surface flow from volcanic eruptions. This concise guide is designed to give students, professionals and keen amateurs of igneous geology the key tools needed to help understand and interpret better the origin and evolution of complex igneous systems in a focused way. This extensively revised and reorganised colour guide builds on the original version by Richard Thorpe and Geoff Brown of the Open University (both now deceased) and published in 1985 as part of the Geological Society of London Field Guide Series. Since then much has changed in igneous petrology including significant advances in our understanding of the physical processes that govern the emplacement of volcanic and plutonic material both on the surface and within the solid earth. For example, new models for the emplacement of pyroclastic flows have helped explain the origin of some of the more enigmatic features of ignimbrites, while magma emplacement studies now draw heavily on techniques used routinely in structural geology. It is thus not enough just to know how to identify minerals in the field – multidisciplinary skills borrowed from other branches of field geology, and even engineering, are not desirable aspirations, but essential must haves. As our understanding of the subject has increased, we have tried in this first colour revision to incorporate much of this new thinking. At the same time we have remained true to the original philosophy of a portable guide that explains clearly and concisely the basic concepts underpinning igneous geology in the field. To this end we hope that the inclusion of new colour images and a colour-coded index system make basic identification of rock types and structure a slightly easier task. Both of us grew up with the original version and it has been a pleasure to revise and build from the start on a text so well laid out. We hope you find the new colour guide as great a companion as we did the old, and that in revised form it is even more of an essential aid when confronted, perhaps for the first time, with igneous rocks in the field.

As we write, the Eyjafjallajokull volcano is erupting in Iceland, causing severe disruption to air traffic across Europe and beyond while generating unexpected but welcome global media interest in volcanology. This excitement will die down soon enough, but a raised awareness and respect for volcanoes will linger in the public psyche for years to come. Its aftermath will present new opportunities to those willing to grapple with the complexity and scientific challenges of ‘next generation’ igneous petrology. Our hope is that this book will in small measure inspire new entrants into the field, just as the original did for us.

Dougal Jerram and Nick Petford

April 2010

Meet the Authors

Dougal is currently at the Department of Earth Sciences, Durham University where he is involved in research and teaching, particularly of field geology. His main expertise is in rock microstructure and textural analysis, 2D–3D modelling of rock textures and volcanic basins, volcanology, sedimentology and field geology. In recognition of his early significant contribution to Earth Sciences he was awarded the Murchison Fund of the Geological Society in 2006. Recently Dougal has developed a keen eye for science outreach, and has appeared on national and inter-national TV (BBC, Discovery, National Geographic, History Channel, Channel 4) promoting aspects of the Earth, and has developed a popular web presence through .

Nick has published extensively on both field and theoretical aspects of igneous geology. After completing a PhD on Andean magmatism and geochemistry he switched to work more on the physical mechanisms governing the ascent and emplacement of granitic magmas and magma rheology. Other research themes include melt segregation in meteorites, the geotechnical properties of volcanic rocks and volcano tourism and economic regeneration. Nick began his research career as a Royal Society University Research Fellow and has worked at the Universities of Liverpool, Cambridge, Kingston and Bournemouth. He was awarded the Murchison Fund of the Geological Society in 1999 and has held visiting professorial appointments in Europe, USA and Australia. Like Dougal he makes the occasional TV appearance. In 2010 he was appointed Vice Chancellor of the University of Northampton.