Preface xi

Acknowledgements xv

1 Introduction and Occurrence 1

1.1 The Importance of Fieldwork 1

1.2 The Global Picture ? Igneous Rocks in Relation to Regional Tectonics 2

1.3 Mode of Occurrence of Igneous Bodies 4

1.4 Summary 11

2 Field Skills and Outcrop Structures 15

2.1 Equipment 15

2.2 Preparing Maps and Basic Mapping 16

2.3 Notebooks and Data Recording 17

2.4 Primary Outcrop Structures 18

2.5 Secondary or Late Stage Outcrop Structures 28

2.6 Outcrop Contact Relationships 32

2.7 Summary of Igneous Outcrop Descriptions 33

3 Igneous Textures and Classification 37

3.1 Describing Rock Types 37

3.2 Colour and Composition 38

3.3 Texture, Grain-Size/Shape and Fabric 43

3.4 Mineral Identification 49

3.5 Naming and Classification 58

4 Volcanics 1 ? Lava Flows 69

4.1 Lava Flow Emplacement Mechanisms 69

4.2 A Compositional Divide for Lava Flows 71

4.3 Mafic/Basaltic Lava Flows 73

4.4 Felsic/Silicic Flows 80

4.5 Pillow Lavas and Hyaloclastites 82

5 Volcanics 2 ? Pyroclastic Rocks 93

5.1 Structures, Textures and Classification 93

5.2 Pyroclastic Flows and Ignimbrites 101

5.3 Scoria Cones 108

5.4 Water/Magma and Sediment/Magma Interactions 109

5.5 Epiclastic Deposits 112

6 Shallow-Level Intrusions 119

6.1 Sill and Dykes 119

6.2 Working Out Emplacement History 124

6.3 Volcanic Plugs and Diatremes 130

6.4 Shallow-Level Subvolcanic Intrusions 133

7 Granitic Complexes 137

7.1 Introduction 137

7.2 General Features and Occurrence 137

7.3 Zoned Plutons 142

7.4 Internal Structures and Textures 145

7.5 Internal Contacts 150

7.6 Emplacement Timing 158

7.7 Distinctive Granitoid Textures 162

7.8 Metamorphic Aureoles 164

7.9 Summary of the Field Characteristics of Granitic Complexes 165

8 Mafic Complexes 171

8.1 General Features and Occurrence 171

8.2 Continental Mafic-Ultramafic Intrusions 173

8.3 Ophiolite Complexes 177

8.4 Komatiites 183

8.5 Summary of the Field Characteristics of Mafic-Ultramafic Intrusions 184

9 Magma Mixing and Mingling 189

9.1 Magma Rheology 189

9.2 Magma Mixing 190

9.3 Magma Mingling 192

9.4 Synplutonic Dykes and Sills 196

9.5 Magma Mingling in Subvolcanic and Volcanic Environments 200

9.6 Xenoliths 201

9.7 A Word of Warning 202

9.8 Summary 203

10 Mineralisation and Geotechnical Properties 207

10.1 Mineralisation and Key Minerals 207

10.2 Mineralisation in Layered Mafic Intrusions 209

10.3 Geotechnical Properties of Igneous Rocks 213

10.4 Rock Mass Classification 216

10.5 Summary 226

Appendix 229

Further Reading 231

Index 233