Building the Cape Verde Islands (eBook)

Ricardo A. S. Ramalho (Autor)

eBook Download: PDF

2011 | 2011
XVIII, 210 Seiten
Springer Berlin (Verlag)
978-3-642-19103-9 (ISBN)

Infos

Hotspots are enigmatic surface features that are not easily explained in the framework of plate tectonics. Investigating their origin is the goal of this thesis, using field evidence collected in the Cape Verde Islands, a prominent hotspot archipelago in the eastern Atlantic Ocean. The approach taken is to document uplift of the islands relative to sea level and use the uplift features to test various models of hotspot development. Island uplift is thought to arise from the growth of the anomalously shallow seafloor on which the islands rest, known as the bathymetric swell, which is characteristic of hotspots.

The work comprises a geological summary and detailed mapping of paleo sea level markers on Cape Verde. Isotopic dating of the markers shows that uplift on the islands over the last 6 Myr is up to 400 m, and that the uplift chronology varies among islands. Two processes act to raise the Cape Verde Islands. The dominant process is one that is local to individual islands. The regional, swell-related component is smaller, and possibly episodic. The observations provide strong constraints on swell development and on hotspot models.

Inhalt

Supervisor’s Foreword 8
Preface 9
Acknowledgments 10
Contents 12
1 Introduction 16
1.1…Introduction 16
1.2…The Growth and Decay of Ocean Island Volcanoes 19
1.2.1 The Prototypical Hawaiian Example 19
1.2.2 The Representativeness of the Hawaiian Example 21
1.2.3 Island Evolution on Fast Moving vs Stationary Plates 23
1.3…Aims and Workflow 24
References 25
2 The Cape Verde Archipelago 28
2.1…Introduction 28
2.2…Geography of the Archipelago 28
2.2.1 Geomorphology 28
2.2.2 Climate and Erosional Regime 31
2.3…Geodynamical Setting 32
2.4…The Cape Verde Rise and Islands 34
2.5…A Heterogeneous Mantle Source 37
2.6…Summary 39
References 39
3 Constraining the Cape Verde Swell Using Numerical Models 42
3.1…Introduction 42
3.2…The Cape Verde’s Bathymetric Swell 43
3.3…Lubrication Model Coupled with Isostatic Uplift 47
3.4…Application of a Flexural Model 54
3.5…Discussion and Conclusions 56
References 59
4 How to Trace Island Freeboard 62
4.1…Introduction 62
4.2…The Concept of Vertical Displacement 64
4.3…Determination of the Present Elevation 65
4.4…The Eustatic Level as a Reference Datum 66
4.5…Palaeo-markers of Sea-level 68
4.5.1 Submarine Volcanic Morphologies 68
4.5.1.1 Pillow and Lobate Lavas 69
4.5.1.2 Pillow Breccias, Hyaloclastites and Other Hydroclastic Products 69
4.5.1.3 Submarine Sheet Flows 71
4.5.1.4 Lava Deltas 74
4.5.1.5 Palaeo-depth Estimation Using Submarine Volcanic Morphologies 75
4.5.2 Marine Sedimentary Formations 77
4.5.2.1 Pelagic and Hemipelagic Sediments 78
4.5.2.2 Coral Reefs 79
4.5.2.3 Shelf and Coastal Sediments 80
4.5.2.4 Palaeo-depth Estimation Using Marine Sedimentary Formations 80
4.5.3 Marine Erosional Morphologies 81
4.5.3.1 Wave-Cut Surfaces 83
4.5.3.2 Insular Shelf Morphology 87
4.6…Summary 88
References 89
5 Tracers of Uplift and Subsidence in the Cape Verde Archipelago 93
5.1…Introduction 93
5.2…Definition of Tracers of Uplift or Subsidence 95
5.3…Tracers of Uplift and Subsidence in the Cape Verde Geological Record 97
5.3.1 Sal 97
5.3.1.1 The Ancient Eruptive Complex 97
5.3.1.2 The Principal Eruptive Formation and the Ponta do Altar-Baleia Complex 101
5.3.1.3 Intercalated Sediments 102
5.3.1.4 The Serra Negra Post-erosional Volcanic Sequence 104
5.3.1.5 Recent Sediments and Last Post-erosional Volcanic Activity 104
5.3.2 Boa Vista 105
5.3.2.1 The Ancient Eruptive Complex 108
5.3.2.2 The Monte Passarão Complex 108
5.3.2.3 The Fundo de Figueiras Formation 108
5.3.2.4 The Monte Caçador Formation 108
5.3.2.5 The Pico Forcado Formation 109
5.3.2.6 Intercalated Sediments 109
5.3.2.7 The Chão de Calheta Formation 109
5.3.2.8 Recent Post-erosional Volcanic Activity 109
5.3.2.9 The Pleistocene Sediments and Wave-cut Surfaces 109
5.3.3 Maio 111
5.3.3.1 The Mesozoic Basement Complex 112
5.3.3.2 The Central Igneous Complex 112
5.3.3.3 The Casas Velhas Formation 112
5.3.3.4 The Pedro Vaz Formation 115
5.3.3.5 The Malhada Pedra Formation 115
5.3.3.6 The Monte Penoso Formation 115
5.3.3.7 Mio-Pliocene Sediments 116
5.3.3.8 Quaternary Sediments and Wave-cut Surfaces 116
5.3.4 Santiago 116
5.3.4.1 The Ancient Eruptive Complex 117
5.3.4.2 The Flamengos Formation 120
5.3.4.3 The Orgãos Formation 120
5.3.4.4 The Pico da Antónia Volcanic Complex 120
5.3.4.5 The Assomada/Monte das Vacas Formation(s) 124
5.3.4.6 Quaternary Sediments and Wave-cut Surfaces 124
5.3.5 Fogo 125
5.3.6 Brava 125
5.3.7 São Nicolau 125
5.3.7.1 The Ancient Eruptive Complex 126
5.3.7.2 The Monte Focinho Late Miocene Marine Sediments 126
5.3.7.3 The Figueira de Coxe Formation 129
5.3.7.4 The Main Eruptive Complex 130
5.3.7.5 The Preguiça and Monte Gordo Formations 133
5.3.7.6 Quaternary Sediments and Wave-cut Surfaces 135
5.3.8 Santa Luzia and Islets 135
5.3.9 São Vicente 136
5.3.10 Santo Antão 139
5.4…Inferences of Uplift and Subsidence 141
5.4.1 Sal 141
5.4.2 Boa Vista 143
5.4.3 Maio 143
5.4.4 Santiago 144
5.4.5 Fogo 144
5.4.6 Brava 144
5.4.7 São Nicolau 145
5.4.8 Santa Luzia and Islets 145
5.4.9 São Vicente 146
5.4.10 Santo Antão 146
5.5…Discussion and Conclusions 146
References 149
6 Dating of Sea-Level Palaeo-Markers 153
6.1…Introduction 153
6.1.1 Types of Samples for Dating Purposes 153
6.2…Palaeontological Dating of Marine Fossiliferous Sediments 155
6.3…Strontium Isotope Stratigraphy on Carbonates 155
6.3.1 Introduction 155
6.3.2 Converting Isotope Ratios into Numerical Ages 157
6.3.3 Single Fossil vs Whole Rock Analysis 159
6.3.4 Sample Information 159
6.3.5 Sample Preparation 159
6.3.6 Sample Chemistry 161
6.3.7 Mass Spectrometry 163
6.3.8 Quality Control 164
6.3.9 Results and Discussion 166
6.3.10 Summary 172
6.4…Laser Ablation U/Th Disequilibrium Geochronology on Fossil Corals 173
6.4.1 Introduction 173
6.4.2 Sample Information 174
6.4.3 Sample Preparation 174
6.4.4 Mass Spectrometry 174
6.4.5 Results and Discussion of Results 175
6.4.6 Summary 176
6.5…Laser Step-Heating {}^{40}/hbox{Ar}/{}^{39}/hbox{Ar} Geochronology on Lavas 176
6.5.1 Introduction 176
6.5.2 Sample Information 177
6.5.2.1 Santiago 177
6.5.2.2 São Nicolau 179
6.5.2.3 Santo Antão 182
6.5.2.4 Sal 182
6.5.2.5 Maio 182
6.5.3 Sample Preparation 182
6.5.4 Mass Spectrometry 182
6.5.5 Results and Discussion of Results 183
6.5.5.1 Santiago 183
6.5.5.2 São Nicolau 185
6.5.5.3 Santo Antão 187
6.5.5.4 Sal 187
6.5.5.5 Maio 187
6.5.6 Summary 187
6.6…Summary 187
References 188
7 Vertical Movements of Ocean Island Volcanoes: Insights from a Stationary Plate 191
7.1…Introduction 191
7.2…Geological Background 193
7.2.1 The Cape Verde Archipelago 193
7.2.2 Santiago 196
7.2.3 São Nicolau 197
7.3…Data 199
7.3.1 Uplift Information Sources 199
7.4…Methods 199
7.4.1 Uplift Calculations 199
7.4.2 Laser Step Heating {}^{40}/hbox{Ar}/{}^{39}/hbox{Ar} Geochronology 200
7.4.3 Laser Ablation MC-ICPMS U-Th Disequilibrium Analysis 202
7.5…Results 203
7.5.1 {}^{40}/hbox{Ar}/{}^{39}/hbox{Ar} Geochronology 203
7.5.1.1 Santiago 203
7.5.1.2 São Nicolau 204
7.5.2 U-Th Geochronology 204
7.5.3 Uplift 204
7.6…Discussion 205
7.7…Conclusions 208
References 209
8 Conclusions 212
8.1…Future Work 218
References 219

Produkt-Details

• Erscheint lt. Verlag: 30.4.2011
• Reihe/Serie: Springer Theses
• Reihe/Serie: Springer Theses
• Zusatzinfo: XVIII, 210 p.
• Verlagsort: Berlin
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Geowissenschaften ► Geologie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie
• Themenwelt: Technik
• Schlagworte: Geology of Cape Verde Archipelago • Hotspot swells • Ocean island evolution • Tracers of relative sea-level on ocean islands • Uplift and subsidence of ocean islands
• ISBN-10: 3-642-19103-7 / 3642191037
• ISBN-13: 978-3-642-19103-9 / 9783642191039