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Preface

Gwenn PERON-PINVIDIC1,2

1 Geological Survey of Norway (NGU), Trondheim, Norway

2 Department of Geoscience and Petroleum, Norwegian University of Science and Technology, Trondheim, Norway

Continental margins mark the transition between continents and oceans, which are the two first-order types of land masses on Earth. Active continental margins are associated with convergent lithospheric plates where collisional processes occur – they are the sites of intense tectonic, seismic and volcanic activity; while passive continental margins correspond to the regions that mark the rupture of a continent and the opening of an ocean basin, ultimately leading to the establishment of an oceanic ridge. Passive margins archive two of the most fundamental geological processes operating on Earth: “rifting” and “breakup”. Passive continental margins, also often referred to as “rifted margins”, register the extension and ultimate separation of the continental lithosphere and the beginning of oceanic crust accretion. After continental breakup, they are tectonically quieter than the active margins.

Rifted margins contribute to our understanding of extensional processes in the continental lithosphere in several ways. First, they represent the most widespread manifestation of Mesozoic and Cenozoic extensional deformation, archiving the structures created during the dismembering of the supercontinent Pangea, a major stage in the tectonic history of our planet. In addition, they border almost all of the land masses that surround the Atlantic, Indian, Antarctic and Arctic Oceans and represent significant surfaces of today’s Earth. Moreover, since they represent the final stage of evolution of an intracontinental rift zone, they can provide a complete record of extensional history and are therefore unique geological features.

Rifted margins are studied by various disciplines of Earth Science (geology, geophysics, geochemistry). Thanks to an increasing amount and better public access to high-quality data, there has been a great improvement in our understanding over the last two decades. However, there are still important debates happening in the scientific community on several questions. Their structural architecture, as well as their spatial and temporal evolution, are still being discussed. No strict consensus has been reached on the composition of the basement, tectonic structures, sedimentary geometries or magmatic content. Correspondingly, their relationship with the adjacent oceanic areas, specifically the first kilometers of oceanic crust, is still largely unconstrained.

Figure P.1. Topographic map of the world with the major ocean basins, rifted margins and main geological structures regularly mentioned in the literature and/or in this book

How to use this book

This book focuses on continental rifted margins, with the aim of explaining the status of knowledge and the way in which understanding has evolved over the last few decades, thanks to the scientific community. Concise text descriptions are used throughout to ensure the content is practical and accessible. We have also incorporated myriad schemas and illustrative figures in all chapters in order to reach a wide audience, particularly students. For further detailed information, the reader is referred to key publications listed under the Further reading sections.

The book is designed to be a useful tool for students and those who are new to the rifted margin community – a sort of “cookbook” to facilitate the reading of scientific publications and provide basic definitions and explanations on a series of key scientific questions. No detailed information is given on the methods: only succinct reminders are provided. If interested, readers are referred to books and contributions specifically dedicated to these topics. Here, the focus is directed towards the rifted margin itself by providing fundamental definitions and explaining how we study these features, how the current theories were developed, where our understanding of rifted margins currently stands and where we are headed as a research community.

Overview

The book comprises two volumes and is structured into three main parts:

Volume 1 includes Parts 1 and 2. Part 1 summarizes all definitions and descriptions necessary for understanding rifted margins. Chapter 1 introduces the basic definitions of the different rift types, followed by a list of the main fault and basin types encountered in rift settings. This list is non-exhaustive but provides basic definitions. The aim is to summarize fundamental terminology so as to avoid any misunderstanding on the use of some terms in the rest of the book, not to propose full definitions. Chapter 2 describes in further detail how rifted margins are classified – spanning the different categories usually found in the literature (e.g. divergent vs. oblique, volcanic vs. non-volcanic, sediment rich vs. sediment starved). The chapter summarizes the evolution of knowledge and understanding achieved by the scientific community over the last few decades, from the initial models proposed in the 1980s to the modern views discussed today. The final part of the chapter then lists and discusses a series of scientific questions selected to illustrate the future scientific challenges our community is facing.

Part 2 explains how we study rifted margins concretely, presenting the four main methods of investigation commonly used to study rifted margins: onshore (Chapter 3), offshore (Chapter 4), numerical modeling (Chapter 5) and analogue modeling (Chapter 6). Chapter 3 explains how rifted margin settings can be studied onshore based on remnants outcropping in orogenic structural contexts. Chapter 4 lists and defines, with illustrative data examples, the main geophysical methods used on a regular basis to image and study modern offshore margins. Chapters 5 and 6 focus on the modeling strategy, including both analogue and numerical approaches.

Volume 2 includes Part 3, which is made up of nine chapters. These chapters illustrate the topics by reviewing a series of case examples considered to be representative of the most discussed study sites at present. The aim of this part of the book is to cover a wide range of rifted margin categories, with both onshore archives and modern offshore cases.

Color code and geological timescale

The following figures provide details of the color code used in most figures in Chapters 1 and 2, if not specified otherwise (Figure P.2), and the geological timescale used throughout this book (Figure P.3).

Figure P.2. Color code used in most figures of this book if not specified otherwise

Figure P.3. Geological timescale

(source: International Commission on Stratigraphy)

Acknowledgments

This book would never have been possible without the valuable help and support of many colleagues and friends.

I would first like to thank the 25 authors who contributed to the various chapters, for their enthusiasm, confidence, professionalism and patience (in alphabetical order): T. Andersen, D. Aslanian, J. Autin, S.P. Chang, P. Chenin, M. Dlescluse, C. Gaina, J. Jakob, H.J. Kjøll, Y. Lagabrielle, S. Leroy, G. Lymer, A. McCarthy, G. Mohn, M. Moulin, C. Nonn, P.T. Osmundsen, M. Perez-Gussinye, B. Petri, M. Pubellier, T. Reston, G. Schreurs, J. Tugend, L. Watremez and F. Zwaan.

Various colleagues also significantly contributed to the finalization of the chapters: reading, reviewing, commenting and correcting our texts and descriptions. Reviewers are rarely mentioned in scientific contributions, yet their role is key to shaping the content. I would like to warmly thank all of them for their significant help (alphabetical order): M. Bonini, D. Franke, M. Gouiza, J. Jakob, A. McCarthy, M. Nirrengarten, A. Rotevatn, K. Senger and Z. Sun.

A special thank you to Joya Tetreault, Per Terje Osmundsen and a dear friend for their corrections, comments and suggestions for Part 1.

I would also like to thank Sylvie Leroy and Yves Lagabrielle for inviting me to write this book, contributing to the Geosciences Encyclopaedia they supervise. Many thanks for your support and confidence during the whole process.

Finally, personally, I would like to thank specific colleagues who have helped me to grow as a researcher through collaborations, discussions, supervisions and debates: Per Terje Osmundsen, Gianreto Manatschal, John Naliboff, Loic Fourel, Tim Redfield, Emmanuel Masini, Espen Torgersen, Katia Svendby and Suzanne McEnroe.

Thank you.

December 2021