Mantle flow and melt generation at mid-ocean ridges

Mantle Flow and Melt Generation at Mid-Ocean Ridges......Page 1
Geophysical Monograph Series......Page 2
Mantle Flow and Melt Generationat Mid-Ocean Ridges......Page 6
CONTENTS......Page 8
PREFACE......Page 9
INTRODUCTION......Page 11
PHYSICAL PROPERTIES......Page 12
AXIAL DEPTHS AND SUBSIDENCE RATES......Page 20
GEOID HEIGHT......Page 26
Seismic Surface Waves......Page 31
Seismic Body Waves......Page 39
The Bottom Line......Page 43
MAGNETUTELLURIC OBSERVATIONS......Page 45
CRUSTAL THICKNESS......Page 48
REFERENCES......Page 68
INTRODUCTION......Page 76
Primary Basalt and Other Concepts......Page 77
Phase Equilibria Constraints......Page 78
Crystallization of MORB at Low Pressures......Page 83
Equilibrium Crystallization......Page 85
Fractional Crystallization......Page 86
Liquid Line of Descent......Page 87
Crystallization of MORB: High Pressure......Page 88
Melting Peridotite......Page 89
P-T Boundaries......Page 90
Melting of Peridotite Sandwiches......Page 92
Melting with Volatiles......Page 96
Abyssal Peridotite......Page 100
Pressure Release Melting......Page 103
OVERVIEW......Page 107
REFERENCES......Page 108
INTRODUCTION......Page 112
Theoretical Considerations......Page 113
Experimental Observations......Page 114
Theoretical Considerations......Page 118
Experimental Observations......Page 121
Theoretical Considerations......Page 123
Experimental Observations......Page 124
Melt Distribution......Page 127
REFERENCES......Page 128
1. INTRODUCTION......Page 131
2.1. Modes of occurrence......Page 132
2.2. Methodology......Page 133
3.1. "Standard" flow pattern: an off- axis record......Page 136
3.2. Paleo-spreading structures and upwelling geometry......Page 139
4. MELT MIGRATION STRUCTURES IN PERIDOTITES......Page 145
4.1. Small-scale structures......Page 146
4.2. Large-scale migration patterns......Page 150
4.3. Discussion......Page 153
5. CONCLUSIONS......Page 157
REFERENCES......Page 158
THE PHYSICS OF MELTING AND MELT MIGRATION......Page 163
POROUS FLOW MIGRATION......Page 164
MATRIX COMPACTION......Page 168
MAGMA FOCUSING......Page 170
MAGMA FRACTURE......Page 171
MANTLE UPWELLING......Page 175
3-D UPWELLING AND RIDGE SEGMENTATION......Page 182
SUMMARY......Page 187
REFERENCES......Page 188
Petrological Systematics of Mid-Ocean Ridge Basalts: Constraints on Melt Generation Beneath Ocean Ridges......Page 191
1. INTRODUCTION......Page 192
1.1 A Working Model......Page 193
2.1 Phase Diagrams......Page 195
2.2 Partition Coefficients......Page 196
2.3 Mass Balance and Simple Equations for Melting and Crystallization......Page 197
2.3.1 Trace Element Patterns......Page 200
2.4 Kd's and Major Element Equilibria......Page 201
3.1 Influence of Low Pressure Fractionation on MORB Compositions.......Page 203
3.2 Correction of Data for Low Pressure Fractionation......Page 205
3.2.1 Interlaboratory Bias......Page 207
3.3 Global Variability of Major Elements in MORB......Page 208
3.4 Regional Variability Around Hot Spots......Page 210
3.5.1 Local Variability on Slow-Spreading Ridges......Page 212
3.5.2 Local Variability on the East Pacific Rise......Page 214
3.6 Summary of Observations......Page 215
4.0 MODELING OF MANTLE MELTING: BACKGROUND AND PREVIOUS WORK......Page 217
4.1 The Importance of Mechanisms of Melt Extraction......Page 219
4.2 The Melting Function......Page 220
4.3.1 An Illustrative Incremental Model......Page 224
4.3.2 Effects of Fractional Melting......Page 227
4.3.3 A Continuous Melting Regime......Page 228
4.3.4 Many Shapes Lead to the Same RMC at Steady-State......Page 229
4.4.1 Experimental Constraints on the Compositional Variations Caused by Partial Melting of the Mantle......Page 230
4.4.2 A Critical Evaluation of Published Chemistry Functions......Page 233
4.5 Results of Previous Attempts to Combine Melting,Mixing and Chemistry Functions......Page 235
5. NEW QUANTITATIVE MODEL FOR MANTLE MELTING......Page 237
5.1.2 Equilibrium and Fractional Melting during AdiabaticDecompression from 20 kbar......Page 239
5.3 Calculation of Equilibrium and Fractional Melting BeneathOcean Ridges......Page 240
6.1 Mean Properties of the Ocean Crust Expected for DifferentMelting Regimes......Page 242
6.1.2 Implications......Page 245
6.2.1 Evaluation of Fractional and Equilibrium Melting Models......Page 246
6.2.2 Evaluation of Mantle Heterogeneity as an Explanation for the Global Compositional Variations......Page 248
6.3 The Origins of Local Major Element Variability......Page 251
6.3.2 Complex Fractionation Models......Page 252
6.3.3 Mantle Heterogeneity and the Local Vector......Page 255
6.3.4 The Slow-Spreading Local Vector Problem......Page 256
6.3.5 Trace Element Evidence......Page 257
6.3.6 Evidence from Ocean Islands: Toxard a Solution to the Local Vector Problem?......Page 258
6.3.7 Local Variability and Ridge Segmentation......Page 259
6.5 Interpretation of MORB Major Element Chemistry......Page 260
7.1 Global Variability of Trace Elements......Page 262
7.2 Local Variability in Trace Elements......Page 264
7.3 Trace Elements and Melting Regime Shape......Page 265
8. SIGNIFICANCE OF SPREADING RATE:A KEY TO UNDERSTANDING THE LOCAL TRENDS?......Page 267
8.1 Spreading Rate and Global Chemical Variability......Page 268
8.2 Spreading Rate and Local Variability......Page 269
8.3 A Model to Account for Contrasts between EPR and MAR Major and Trace Element Data......Page 270
9. CONCLUSIONS......Page 272
APPENDIX A: CALCULATION OF FEO, MGO, NA20 AND TIO2 DURING ADIABATIC MELTING OF THE MANTLE......Page 273
APPENDIX B: OLIVINE LIQUID PARTITIONING AS A FUNCTION OF TEMPERATURE, PRESSURE AND LIQUID COMPOSITION......Page 275
C.1 Periodically Replenished Magma Chambers PRMC's......Page 277
C.3 High Pressure Fractionation......Page 279
C.3.1 General Results of High Pressure Fractionation......Page 281
C.3.2 Models for High Pressure Fractionation......Page 282
REFERENCES......Page 284
Melt Generation Processes......Page 289
Melt Modification Processes......Page 290
Experimental Procedure......Page 291
Attainment of Equilibrium and Conservation of Mass......Page 292
Constraints From Simple System Experiments......Page 296
Constraints from Experiments on MORB and MORB-Analog Compositions......Page 297
Estimating the Fractionation History of MORB Suites......Page 301
The Pyroxene Paradox......Page 303
Calcic Plagioclase in MORB Lavas......Page 304
Residues of Elevated Pressure Fractionation in Mantle Peridotite......Page 305
Role of Fractional Crystallization in the Development of Local Trends......Page 306
SUMMARY......Page 311
Calculation of Fractional Crystallization Paths......Page 312
REFERENCES......Page 316
1. INTRODUCTION......Page 319
2b. 3-D Boundary Element flow model......Page 321
4. OBSERVED BATHYMETRY AND MANTLE BOUGUER ANOMALIES......Page 323
5. PREDICTED BATHYMETRY AND MANTLE BOUGUER ANOMALIES......Page 328
6a. Shape of the plate at the axis......Page 329
6b. Mantle rheology......Page 331
6c. Fit of model results to data......Page 332
REFERENCES......Page 333
1. INTRODUCTION......Page 335
2. SMALL-SCALE CONVECTION......Page 336
2.1. Model Geometry and Boundary Conditions......Page 337
2.3. Results and Discussion......Page 338
3. INTRODUCTION TO THE EFFECTS OF MELTING ONMANTLE FLOW......Page 341
3.3. Melting and Mantle Flow......Page 342
3.4. Simulation of Eruption......Page 344
4.1. The Effect of Small-Scale Convection on Melting......Page 346
4.2. Variation with Plate Velocity......Page 347
5. DISCUSSION......Page 348
5.1. Segmentation and Episodicity......Page 349
5.2. The Composition of Mid- Ocean Ridge Basalts......Page 350
5.3. Gravity and Topography......Page 353
APPENDIX A: THE MATHEMATICAL MODEL......Page 354
A.1. Momentum Equations......Page 355
A.2. Conservation of Energy and the Melting Process......Page 356
B.1. Weak Convection......Page 357
B.2. Strong convection......Page 358
REFERENCES......Page 359
INTRODUCTION......Page 361
MODELING......Page 363
RESULTS......Page 365
CONCLUSIONS......Page 367
REFERENCES......Page 368