The Field Description of Metamorphic Rocks. Dougal Jerram

PREFACE – THE FIELD DESCRIPTION OF METAMORPHIC ROCKS

      In many regards, metamorphic rocks represent some of the most complicated challenges that you will find in the field. They were obviously once igneous, sedimentary, or even different metamorphic rocks, and you may be able to interpret some of this early history at the outcrop. But they have subsequently been changed through combinations of pressure, temperature, and reaction with fluid so that they might now look radically different to their original form. In order to understand these changes (the rock’s metamorphosis), and to some extent the original ‘parent’ rock, the field description of metamorphic rocks requires careful observation and a grasp of many aspects of the broader range of the geosciences. It is not enough just to know how to identify key metamorphic minerals in the field: multidisciplinary skills borrowed from other branches of field geology, and even engineering, are increasingly essential requirements for the modern metamorphic geologist.

      This concise guide is designed to give students, professionals, and keen amateur geoscientists the key tools needed to help understand and interpret the origin and evolution of complex metamorphic systems in a focused way, while in the field. This extensively revised and reorganised colour guide builds on Norman Fry’s original version, published in 1984 as part of the (then) Geological Society of London Field Guide Series. Since 1984, much has changed in the scientific community’s understanding of metamorphic processes and in the ways that fieldwork is conducted. Accordingly, we have tried in this first colour revision to incorporate much of this newer thinking and methodology. At the same time, we have aimed to remain true to the original philosophy of a portable guide that concisely explains the basic concepts underpinning the field description of metamorphic rocks. Indeed, we have kept and built on some sections of Fry’s original text. The original version was necessarily limited by its black and white printing, and we have enjoyed updating the figures in this version: almost every figure in the original book has been replaced here or reproduced in colour. We hope that the inclusion of the new colour images and a simple, colour‐coded index system will help the reader to navigate their way through the different types, grades, and origins of metamorphic rocks. Both authors grew up with the original versions of the Geological Field Guide Series and one of us (Dougal) was even taught by Norman Fry at Cardiff University. So it has been a great pleasure, if not a long journey, to revise this field handbook, now published as part of Wiley Blackwell’s ‘Geological Field Guide Series’. We hope you find this new guide a great companion and an essential aid when confronted, perhaps for the first time, with metamorphic rocks in the field.

       Dougal Jerram and Mark Caddick 2021

Preface – Meet the Authors

      Dougal holds a 20% research professorship at the University of Oslo and is the director of DougalEARTH Ltd. He is primarily a field geologist and has undertaken fieldwork all over the world and experienced a wide range of Earth’s geology and landscapes from Africa to Antarctica. He started his geological career in the UK, where he cut his teeth on the many fundamental outcrops the UK has to offer through a classic Geology degree at Cardiff and a PhD at Liverpool. His main expertise is in rock microstructure and textural analysis, 2D–3D modelling of rock textures, and understanding aspects of volcanic rifted margins from a hard rock basis. In recognition of his early significant contribution to Earth Sciences, he was awarded the Murchison Fund of the Geological Society in 2006. Dougal has written a number of other books centred around the Earth Sciences for both adults and children. He is also keen on science outreach and has been a presenter on Discovery channel’s The Very Edge of China (2019), Hardest Job (2017), BBC’s Fierce Earth series (2013–14), Operation Grand Canyon (2014), as well as appearances on National Geographic, Smithsonian Channel, Eden, Channel 4, and Abandoned Engineering.

      Mark is an Associate Professor at Virginia Tech. A metamorphic petrologist, his work focuses on the micro‐scale processes that lead to changes in rock mineralogy and texture, and the tectonic‐scale processes that these may reveal. He has worked on metamorphic rocks from a variety of settings and with a wide range of styles, spanning from cold, deep subduction to high temperature crustal melting. Though much of his research is lab based or computational, it invariably starts in the field. He also works on high energy impacts and high temperature reactions of minerals in jet engines – which he obviously thinks of as a form of metamorphic geology! Mark was a student in the UK, at the universities of Bristol and then Cambridge, before moving to Switzerland as a research scientist at ETH Zurich. He has been in Virginia since 2012, during which time he has taught, amongst other things, an introduction to the geosciences, igneous and metamorphic petrology, thermodynamics, and field‐based courses.

ACKNOWLEDGMENTS

      First and foremost, we would like to thank Norman Fry, whose original book was an important guide for both authors as students, and he is also thanked for giving us the go ahead to update the book and to provide all the original materials that formed an invaluable framework as we planned this revised version. This book has taken a long time to mature and we must thank the support and patience of the team of people at Wiley Blackwell and associated editorial groups (both past and present) who have helped to get the book finished. We must particularly thank (and apologies if we miss anyone); Mandy Collison, Andrew Harrison, Frank Weinreich, Emma Cole, Shiji Sreejish, Priyadharshini Arumugam, Bobby Kilshaw, Athira Menon, Nithya Sechin, Vinodhini Mathiyalagan, Audrie Tan, Fiona Seymour, Ian Francis, Delia Sandford, and Rachael Ballard. Many people directly contributed figures and photographs and input to this book scientifically and these are particularly thanked for their help and open sharing of information, including (in no particular order); Isabela Carmo (with additional help from Prof. Renata S. Schimdt – UFRJ), Hans Jørgen, Nick Timms, Steve Reddy, Richard Brown, John Schumacher, John Howell, Susanne Schmid, Jim Talbot, Christoph Schrank, Bob Tracy, Claudio De Morisson Valeriano, Clayton Grove, Dave Prior, Tonje Lund, Nigel

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