Faulting and Magmatism at Mid-Ocean Ridges

Faulting and Magmatismat Mid-Ocean Ridges......Page 3
CONTENTS......Page 5
PREFACE......Page 6
INTRODUCTION......Page 7
Mechanisms......Page 8
DETERMINISTIC AND STOCHASTIC SEA FLOOR MORPHOLOGY......Page 10
EMPIRICAL ORTHOGONAL FUNCTION ANALYSIS......Page 11
Separation of Axial Morphology and Flanking Roughness......Page 12
Roughness Estimates......Page 14
Global Variations in Axial Relief Width, Roughness and Depth......Page 16
Depth Estimates......Page 17
Correlations......Page 18
Spreading Center Depth......Page 19
Seafloor Roughness and Axial Morphology......Page 20
Transitional Spreading Centers......Page 21
Spreading Rate Dependence and Variability of Axial Valley Environments......Page 23
Spreading Rate Dependence of Internal Structure......Page 24
Spreading Rate, Stability and Episodicity......Page 26
SUMMARY......Page 27
REFERENCES......Page 28
INTRODUCTION......Page 32
LARGE SCALE VARIATIONS IN AXIAL MORPHOLOGY; CORRELATIONS WITH MAGMA SUPPLY AND SEGMENTATION.......Page 33
FINE SCALE VARIATIONS IN RIDGE MORPHOLOGY WITH IN THE AXIAL NEOVOLCANIC ZONE......Page 45
FAULTING ON INTERMEDIATE- TO FASTSPREADING RIDGES......Page 49
VOLCANIC GROWTH FAULTS AND ABYSSAL HILLS IN THE PACIFIC......Page 51
FUTURE WORK......Page 54
REFERENCES......Page 59
Magmatism at Mid-Ocean Ridges: Constraints from Volcanological and Geochemical Investigations......Page 64
2.1. The Neovolcanic Zone......Page 66
2.2. Off-Axis Volcanism......Page 73
2.3. Morphological Variations in Submarine Lava Flows......Page 79
3.1. Detectiona nd Observation of Volcanic Events on theMid-Ocean Ridge......Page 84
3.2. Graben Faulting Associated with Recent Eruptive Events......Page 89
4. ANALYTICAL DATING TECHNIQUES FORYOUNG LAVAS......Page 91
4.1. Samplinga nd Qualitative Dating Methods......Page 92
4.2. Radiometric Dating of MORB......Page 93
4.3. Age Constraints from Dating......Page 98
5. COMPOSITIONAL VARIATIONS OF MID-OCEAN RIDGE BASALTS......Page 99
5.1. Segment-Scale and Local Variability......Page 100
5.2. Flow-Scale Variability......Page 105
5.3. Volume-Rate Relationships......Page 109
6. DISCUSSION AND CONCLUSIONS......Page 110
REFERENCES......Page 111
1. INTRODUCTION......Page 121
2.1. Mechanics......Page 122
2.3. Sequence of Events During Dike Intrusion......Page 123
3.1. Fast-Spreading Ridges......Page 126
3.2. Slow-Spreading Ridges......Page 128
3.4. Frequency of Dike Intrusion Events at Different Spreading Rates......Page 129
4.1. Consequences of Dike Intrusion at Fast-Spreading Ridges......Page 130
4.2. Consequences of Dike Intrusion at Slow-Spreading Ridges......Page 133
4.3. Dike Intrusion and Megaplumes......Page 134
REFERENCES......Page 135
INTRODUCTION......Page 141
Background From Fracture Mechanics......Page 142
Fissure Length, Width and Depth......Page 144
Models of Fissure Development......Page 145
FISSURING AT DEPTH: IMPLICATIONS FOR FAULTING WITHIN THE NEOVOLCANIC ZONE......Page 146
TECTONIC VERSUS ERUPTIVE FISSURING: LINKAGES TO RIDGE SEGMENTATION ANDMAGMATISM......Page 147
IMPLICATIONS OF FISSURING FOR VOLCANIC TECTONICCYCLING AT FAST-SPREADING RIDGES......Page 148
CONCLUSION: DIRECTIONS FOR FUTURE RESEARCH......Page 149
REFERENCES......Page 151
Ultramafic-Mafic Plutonic Rock Suites Exposed Along the Mid-Atlantic Ridge10øN-30øN. Symmetrical-Asymmetrical D istribution and Implications for Seafloor Spreading Processes......Page 156
2. A REVIEW OF THE OCCURRENCES OF DEEP CRUSTAL AND MANTLE ROCKSALONG THE MAR AXIS......Page 157
2.1. The Eastern Ridge-Transform Intersection at the Oceanographer Fracture Zone......Page 158
2.2. Segment OH3, North of the Hayes Fracture Zone......Page 159
2.3. The MARK Area......Page 162
2.5. The Fifteen Degrees North Region......Page 165
3.1. Various Tectonic Settings......Page 171
3.3. Crustal Stretching and Low Magma Budgets......Page 173
3.4. Symmetrical and Asymmetrical Distribution of Lithologies Along Axis......Page 175
REFERENCES......Page 176
1. INTRODUCTION......Page 180
2. EVOLUTION OF THE CURRENT VIEW OF OCEANIC LITHOSPHERE......Page 181
3.1 Settings of Tectonic Windows......Page 185
3.2 Faults, Fault-Line Scarps, and Seafloor Escarpments......Page 186
3.3 Major Rock Units of the Oceanic Lithosphere......Page 189
4.2 Tectonic Windows in to Slow-Spread Lithosphere......Page 198
4.3 Implications for Processes at Slow-Spreading Ridges......Page 202
4.4 Tectonic Windows into Intermediate-to Fast-Spread Lithosphere......Page 205
4.5 Implications for Processeast Intermediate to- Fast-Spreading Ridges......Page 207
5. CONCLUDING REMARKS......Page 211
REFERENCES......Page 213
Structure of Modern Oceanic Crust and Ophiolites and Implications for Faulting and Magmatism at Oceanic Spreading Centers......Page 222
1. INTRODUCTION......Page 223
2. OPHIOLITE-OCEAN CRUST ANALOGY......Page 225
4.1. Slow-spreading Oceanic Crust......Page 228
4.2. Intermediate-spreading Oceanic Crust......Page 233
4.3. Fast-spreading Oceanic Crust......Page 234
5. INTERNAL STRUCTURE OF ANCIENT OCEANIC CRUST AS OBSERVED IN OPHIOLITES......Page 236
5.1. Ophiolites with Inferred Slow-Spread Origin......Page 238
5.2. Ophiolites with Inferred Fast-to Intermediate-spread Origin......Page 242
6.1. Magmatism and Crustal Deformation at Fast- to Intermediate-Spreading Ridges......Page 250
6.2. Crustal Deformation and the Role of lnterplay between Faulting and Magmatism at Slow-Spreading Centers......Page 252
6.3. Serpentinizationand Tectonism......Page 256
6.5. Effects of Thermal Structure and Magma Supply in Oceanic Crust Generation......Page 258
7. CONCLUSION......Page 261
REFERENCES......Page 262
1. INTRODUCTION......Page 269
1.2. Physical Models for Periodic Formation of Melt-Filled Fractures From Magma Chambers......Page 270
1.3. Origin of Modal Layering in Gabbros......Page 271
1.5. Sills in the MTZ Beneath Fast- to Medium-Spreading Ridges......Page 272
2. CRYSTALLIZATION OF ASCENDING BASALT NEAR THE MTZ......Page 273
3. PERMEABILITY BARRIERS AT THE MTZ......Page 275
5. MODEL FOR BEHAVIOR OF A CONTINUOUSLY FILLED MELT LENS......Page 277
5.1. Non-dimensionalization......Page 279
5.2. Solution:......Page 280
6. SCALED CALCULATIONS, AND COMPARISON TO OBSERVED PHENOMENA......Page 281
7.1. Modally Graded Layering in Gabbro Lenses......Page 282
8.1. More Layers Than Dikes: Several Melt Lenses With in the Crust?......Page 283
8.2. Crystallization Temperatures for Gabbras and Thermal Structure Beneath Ridges......Page 285
8.3. Igneous Accretion of the Lower Oceanic Crust......Page 286
REFERENCES......Page 288
INTRODUCTION......Page 292
EXPERIMENTAL CONSTRAINTS ON THE RHEOLOGY OF THE LOWER OCEANIC CRUST......Page 293
Geochemical and Petrologic Constraints......Page 297
Geological and Geophysical Constraints......Page 298
IMPLICATIONS......Page 299
REFERENCES......Page 301
INTRODUCTION......Page 305
PREVIOUS MODELS FOR AXIAL VALLEYS......Page 306
Rheology......Page 309
Numerical Method......Page 310
RESULTS FOR STRETCHING A SINGLE LAYER......Page 311
Simple Scaling of Axial Valley Relief and Brittle Layer Geometry......Page 312
Effect of Cohesion Reduction with Strain......Page 313
Analysis of Model Abyssal Hills......Page 316
Model Formulation Including Crust......Page 317
Results for Models with Intruded Crust......Page 319
CONCLUSIONS......Page 320
REFERENCES......Page 322
INTRODUCTION......Page 324
Growth of lndividual Faults......Page 328
Growth of Simple Fault Arrays......Page 329
Growth of Fault Populations......Page 332
Depth of Fault Nucleation......Page 336
Width of the Fault Generation Zone......Page 337
Fault Development and d-L Scaling......Page 341
SUMMARY AND CONCLUSIONS......Page 342
REFERENCES......Page 344