The Variscan Belt of Western Europe, Volume 1 History, Geodynamic Context and Early Orogenic Events

This book deals with the geological record and the evolution of ideas concerning the Variscan orogenic belt in France and neighboring regions.

Volume 1 is based on a general introduction concerning the imprint of the Variscan period on the geology of France, as well as on the particularities of the study of this ancient orogen. A history of the concepts applied to the Variscan belt is proposed in order to consider this orogen in the history of Earth Sciences. A paleogeodynamic analysis of the Variscan cycle sets the general framework for the evolution of the orogen, which is then tackled through the prism of the magmatic, metamorphic and tectonic record of the early phases (from Cambrian to Lower Carboniferous).

Volume 2 proposes an analysis of the late evolution of the Variscan orogenic belt, reflecting its dismantling in a high-temperature context during the Upper Carboniferous and Permian. The sedimentary archives are described, as well as the questions raised by the specificities of this ancient orogen.

Yoann Denèle is a structural geologist, specializing in the tectonic evolution of the ductile domains of orogens.

Julien Berger is a petrologist, specializing in the magmatic and metamorphic evolution of ancient orogenic belts and magmatic arcs.

Preface ix
Yoann DENÈLE and Julien BERGER

Introduction xi
Yoann DENÈLE and Julien BERGER

List of Figures xxi

Chapter 1 The Variscan Belt: History of the Evolution of Methods and Concepts 1
Olivier VANDERHAEGHE

1.1 Introduction 1

1.2 Beginnings of geology, from the Renaissance to the Industrial Revolution 3

1.2.1 From Earth’s history to regional geology 3

1.2.2 Stratigraphy of the Paleozoic at the front of the Variscan belt 5

1.2.3 Concepts of deep magmatism and metamorphism 7

1.2.4 Microscopic analysis of crystalline rocks 9

1.2.5 Theory of magmatic uplifting 10

1.2.6 Geosynclinal theory developed from the Appalachians 12

1.2.7 Mountain belt vergence theory 13

1.3 Debate between fixists and mobilists from the late 19th to early 20th centuries 14

1.3.1 Geosynclinal theory and the European Variscan belt 14

1.3.2 Zoneography of metamorphism in the Variscan belt 15

1.3.3 Nappes, migmatites and plutons of the internal Variscan belt 18

1.3.4 The Variscan belt and continental drift 23

1.4 Unification of the Earth sciences in the late 1960s 27

1.4.1 The Variscan belt at the time of plate tectonics 27

1.4.2 Principal sutures and continental blocks 29

1.4.3 Paleogeographical reconstructions 31

1.4.4 Geodynamic tectonic models 31

1.5 Conclusion and challenges of the 21st century 33

1.6 References 34

Chapter 2 Paleogeographical and Paleo-Geodynamic Context of the Variscan Belt 47
Jean-Marc LARDEAUX and Karel SCHULMANN

2.1 Introduction 47

2.2 Litho-tectonic zonation of the Variscan belt and identification of the principal "paleogeographical domains": contribution of great precursors and evolution of ideas 48

2.3 Paleogeographic reconstructions: paleontological, paleo-climatological and mineralogical data 69

2.4 Paleomagnetic data and paleogeographic reconstructions 77

2.4.1 First investigations: 1980-2010 77

2.4.2 Paleomagnetic, mantle and unified kinematic models: 2010-2020 82

2.5 Concluding remarks 88

2.6 References 89

Chapter 3 Pre-collision Magmatism 111
Julien BERGER

3.1 Introduction 111

3.2 Cadomian magmatism in brief 112

3.3 Geochronological data: two magmatic phases in the Lower Paleozoic 113

3.4 Cambrian-Ordovician magmatism 117

3.4.1 Ophiolites 117

3.4.2 Metabasites: amphibolites, eclogites and basic granulites of allochthonous units 121

3.4.3 The leptyno-amphibolite complex 125

3.4.4 Orthogneisses of allochthonous metamorphic units 126

3.4.5 Magmatism of autochthonous and para-autochthonous units 130

3.4.6 Summary, petrogenic and geodynamic proposals 133

3.5 Devonian magmatism 139

3.5.1 Calc-alkaline plutons 140

3.5.2 Subalkaline lava 142

3.5.3 Central and North American dolerites 143

3.5.4 The ophiolites issue 143

3.5.5 Summary, petrogenic and geodynamic proposals 145

3.6 Conclusions and perspectives 147

3.7 References 148

Chapter 4 Early Metamorphisms and Deformations in the French Variscan Belt 163
Michel FAURE

4.1 Introduction 163

4.2 Metamorphisms and deformations in the Moldanubian domain 165

4.2.1 Eo-Variscan events 170

4.2.2 Lower Carboniferous Variscan tectono-metamorphic events 180

4.3 Metamorphisms and deformations in the Saxothuringian domain 193

4.4 Metamorphisms and deformations in the eastern Variscan branch 195

4.4.1 Massifs free of alpine superimposition: Maures-Tanneron and Corsica-Sardinia Massif 195

4.4.2 Alpine Variscan substratum 202

4.5 Conclusion 207

4.6 References 208

List of Authors 227

Index 229

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