GEODYNAMICS: CRUSTAL DEFORMATION AND DIVERGENT PLATE TECTONICS

By E. NONIK

CONTENTS 1 INTRODUCTION 1 2 MANTLE PLUME-MID-OCEAN RIDGE INTERACTION IN THE NORTH ATLANTIC 5 21 GEOLOGY OF THE NORTH ATLANTIC: THE ICELAND HOTSPOT 211 THE MID-ATLANTIC RIDGE 5 212 THE NORTH ATLANTIC LARGE IGNEOUS PROVINCE 6 213 GEOCHEMICAL VARIATIONS 214 GRAVITY AND GEOID ANOMALIES 9 12 22 OPENING OF THE NORTH ATLANTIC 221 MAGNETIC RECORDING OF SEA FLOOR SPREADING 222 GEOLOGIC AND GEODETIC PLATE MOTION MODELS 223 GEODETIC MEASUREMENTS IN ICELAND 23 SEISMIC STRUCTURE OF THE ICELAND MANTLE PLUME 231 PLUME STRUCTURE IN THE UPPER MANTLE 12 12 232 PLUME STRUCTURE IN THE LOWER MANTLE: A RESOLUTION PROBLEM 18 233 AN ALTERNATIVE TO THE PLUME MODEL 19 24 PLUME MODELS: EXCESS TEMPERATURES AND ENERGETICS 20 92 25 PLUME-RIDGE INTERACTION AND THE ICELAND HOTSPOT SWELL 21 251 TOPOGRAPHY AND GRAVITY 21 252 V-SHAPED RIDGES 23 26 MOVEMENT OF THE MAR RELATIVE TO THE ICELAND MANTLE PLUME: THE HOTSPOT TRACK 3 TECTONIC FRAMEWORK GEOLOGY 31 311 THE TERTIARY 312 THE PLIO-PLEISTOCENE (UPPER PLIOCENE AND LOWER PLEISTO- 313 UPPER PLEISTOCENE 314 THE POSTGLACIAL 32 THE PLATE BOUNDARY IN ICELAND 321 VOLCANIC ZONES 322 TRANSFORMS 33 SEGMENTATION OF THE VOLCANIC ZONES: VOLCANIC SYSTEMS 34 RIFT JUMPS AND PAST PLATE BOUNDARIES 35 VOLCANIC ACTIVITY IN HISTORICAL TIMES: WRITTEN RECORDS OF 1,100 YEARS 36 OVERVIEW OF SEISMICITY OF ICELAND 4 CRUSTAL STRUCTURE OF ICELAND 41 SEISMIC CONSTRAINTS ON CRUSTAL THICKNESS 42 GRAVITY AND ISOSTATIC BALANCE OF ICELAND 43 THERMAL STRUCTURE OF THE CRUST 431 HEAT FLOW 432 SEISMIC OBSERVATIONS 433 MODELS OF THERMAL STRUCTURE 44 THE PÁLMASON MODEL OF CRUSTAL KINEMATICS 5 VOLCANO DYNAMICS 6 51 VOLCANIC EDIFICES AND STYLES OF MAGMATIC ACTIVITY 52 VOLCANO INTERIORS: GEOLOGIC AND GEOPHYSICAL CONSTRAINTS 53 MODELLING OF VOLCANO DEFORMATION 531 THE MOGI MODEL 532 ESTIMATION OF MAGMA VOLUMES FROM THE MOGI MODEL 533 MODELLING MAGMA SOURCES AS SILLS, DIKES, AND ELLIPSOIDAL SOURCES 23 38 38 555000 69 71 78 81 14 82 15 534 FEEDER CHANNELS FOR MAGMA CHAMBERS AND SHALLOW IN- 17 TRUSIONS 84 17 535 FAILURE CRITERIA FOR ERUPTIONS 85 THE KRAFLA VOLCANIC SYSTEM AND ITS 1975-1984 RIFTING EPISODE 86 54 55 CALDERAS: THE 1875 CALDERA-FORMING ERUPTION AT ASKJA AND CURRENT UNREST 551 THE 1874-1875 RIFTING EPISODE AT ASKJA 95 552 CURRENT UNREST AT ASKJA VOLCANO 56 HEKLA: ONE OF ICELAND'S MOST ACTIVE VOLCANOES 95 97 ACTIVAT 57 ADDITIONAL EXAMPLES OF VOLCANO UNREST: GRÍMSVÖTN, KATLA, HENGILL, AND EYJAFJALLAJÖKULL VOLCANOES 58 OVERVIEW AND IMPLICATIONS 100 6 THE PLATE-SPREADING DEFORMATION CYCLE 103 61 CONTINUOUS GPS MEASUREMENTS 103 62 INTER-RIFTING DEFORMATION 105 621 MEASUREMENTS IN NORTH ICELAND PRIOR TO THE KRAFLA RIFTING EPISODE 105 622 INTER-RIFTING DEFORMATION AT OVERLAPPING RIFT ZONES SOUTH ICELAND 106 623 MODELS OF INTER-RIFTING DEFORMATION 109 624 VERTICAL RIFT ZONE DEFORMATION DURING INTER-RIFTING PERIODS 110 63 RIFTING EVENTS 631 MODELS OF RIFTING EVENTS 116 112 64 POST-RIFTING ADJUSTMENT 117 641 NEWTONIAN VISCOSITY MODELS OF POST-RIFTING DEFORMATION 122 642 VISCOELASTIC MODELS OF POST-RIFTING DEFORMATION 124 643 ELASTIC DIKE-OPENING MODELS OF POST-RIFTING DEFORMATION 126 65 OBLIQUE SPREADING: THE REYKJANES PENINSULA 126 129 66 THE RIFTING CYCLE 7 BREAKING THE CRUST: SEISMICITY AND FAULTING 133 71 THE TJÖRNES FRACTURE ZONE 133 72 THE SOUTH ICELAND SEISMIC ZONE: "BOOKSHELF FAULTING" 136 721 MICROEARTHQUAKE ACTIVITY AND STRUCTURE OF THE SOUTH ICELAND SEISMIC ZONE 136 722 SHEARING ACROSS THE SOUTH ICELAND SEISMIC ZONE 723 EARTHQUAKE SEQUENCES AND BOOKSHELF FAULTING 138 140 73 THE 2000 EARTHQUAKE SEQUENCE 143 731 HYDROLOGICAL SIGNATURES OF EARTHQUAKE STRAIN 147 147 732 TRIGGERING OF EARTHQUAKES 74 ASEISMIC SLIP: SLOW EARTHQUAKE AT KLEIFARVATN? 149 75 POST-SEISMIC DEFORMATION 149 76 EARTHQUAKE PREDICTION RESEARCH 150 8 GLACIAL ISOSTASY AND SEA-LEVEL CHANGE: RAPID VERTICAL MOVEMENTS AND CHANGES IN VOLCANIC PRODUCTION RATES 151 81 SEA-LEVEL CHANGE IN ICELAND 151 153 82 POSTGLACIAL REBOUND IN ICELAND 153 156 821 THE GLACIAL HISTORY 822 OBSERVATIONS OF GLACIO-ISOSTATIC REBOUND 160 83 VARIABLE VOLCANIC PRODUCTION RATES AT THE END OF THE LAST GLACIATION 164 823 MODELLING ACTIVATE V GO TO 84 HISTORICAL ICE VOLUME CHANGES AND RECENT FLUCTUATIONS IN LAND ELEVATION 99 166 85 MELTING OF ICECAPS BY GLOBAL WARMING: AN EXPERIMENT IN RHEOLOGY 9 ICELAND GEODYNAMICS: OUTLOOK 175 172 REFERENCES 185