Geomagnetism: Treatise on Geophysics

Cover......Page 1
Editor-in-Chief......Page 2
Volume Editors......Page 3
Preface......Page 4
Early History......Page 7
Early Chinese Compasses......Page 8
Epistola of Petrus Peregrinus......Page 10
European Recognition of Declination......Page 12
De Magnete of William Gilbert......Page 13
Further Developments in Observations......Page 14
Measurement of Intensity......Page 15
Deciphering the Past Using Remanent Magnetization......Page 17
Polarity Reversals......Page 18
Long-Term Behaviors of the Geodynamo......Page 20
Spherical Harmonic Analysis......Page 21
Satellite Measurements......Page 23
Geomagnetic Spectrum......Page 24
Inverse Problem......Page 26
Signal and Noise in Magnetic Field Measurements......Page 28
Magnetic Mapping of Planets......Page 30
Planetary Dynamos: A Comparative study......Page 32
The Magnetic Field of the Sun......Page 33
Discussion and Conclusions......Page 35
References......Page 36
Introduction......Page 38
Magnetic Elements, Coordinates,
and Time......Page 40
Dipole coordinates and components......Page 41
Time......Page 42
Ground Data......Page 43
Satellite Data......Page 44
Ørsted......Page 45
Calibration and alignment of satellite magnetometers......Page 46
Dst,
an index of magnetospheric ring-current strength......Page 47
Global Models of the Earth’s Magnetic Field......Page 48
Spherical Harmonic Representation of the Field......Page 49
The International Geomagnetic Reference Field......Page 50
More advanced models......Page 51
Models of the Core Field......Page 53
Models of the Crustal (Lithospheric) Field......Page 55
Modelling philosophy......Page 56
Early comprehensive models......Page 58
Recent comprehensive models......Page 59
Predictions from CM4......Page 60
Spatial Power Spectra and Timescales......Page 64
The Field at the Earth’s Surface......Page 68
The Field at the Core Surface......Page 73
References......Page 77
Relevant Websites......Page 80
Introduction......Page 81
Magnetosphere......Page 82
Currents......Page 83
Single-Particle Motion......Page 84
Collisions and Conductivity......Page 86
Convection and Merging......Page 87
Equatorial Electrojet......Page 88
Storms and Sudden Commencements......Page 89
Magnetospheric Convection......Page 90
Auroral Electrojets......Page 91
Substorms......Page 92
Geomagnetic Pulsations......Page 93
Pi2 Pulsations......Page 94
References......Page 95
5.04 Observation and Measurement Techniques......Page 97
nomenclature......Page 98
Instrumentation......Page 99
The induction coil......Page 100
The fluxgate......Page 101
The SQUID......Page 102
Proton precession magnetometers......Page 103
Optically pumped magnetometers......Page 105
Special Magnetic Conditions in an Observatory......Page 107
Absolute measurement of the horizontal component, H, by the Gauss method......Page 108
Absolute measurements with the proton vector magnetometer (PVM)......Page 109
Declinometer......Page 110
DIflux (DIM)......Page 111
Classical magnet-based instruments......Page 112
Calibration of scalar magnetometers......Page 113
Obtaining definitive absolute data......Page 114
The INTERMAGNET Magnetic Observatory Network......Page 115
Fully Automatic Magnetic Observatories......Page 116
Magnetic Surveys for Geological Exploration......Page 117
Mapping Magnetic Anomalies......Page 118
The Origin of Magnetic Anomalies......Page 119
Ground surveys......Page 122
Practical airborne magnetometry......Page 123
Elimination of nongeological influences (aircraft,
temporal changes)......Page 124
Data Presentation,
Enhancement and Interpretation Methods......Page 126
The Link between Magnetic Properties of Rocks and Regional Geology......Page 128
Satellites and Space Probes......Page 130
Introduction......Page 131
Consolidated rocks......Page 132
Unconsolidated (lake and deep sea) sediments......Page 133
Astatic systems......Page 134
Spinner magnetometers......Page 135
Cryogenic magnetometers......Page 136
Introduction......Page 138
Thermal demagnetization......Page 139
Intensity of magnetization against demagnetization level......Page 140
Remagnetization circles......Page 141
Paleomagnetic directions: the Fisher distribution......Page 142
Field tests......Page 143
Baked contact test......Page 144
The GAD hypothesis......Page 146
References......Page 147
Relevant Websites......Page 150
5.05 Geomagnetic Secular Variation and Its Applications to the Core......Page 151
Historical Background......Page 152
Catalogs and Compilations of Data......Page 153
Surveys, Repeat Stations,
and Marine Data......Page 154
Observatory Data......Page 156
Satellite Data......Page 159
Time-Dependent Models of the Main Field......Page 160
Methodologies......Page 161
Time-dependent models based on cubic B-splines......Page 163
The ufm1, ufm2,
and gufm1 models......Page 164
CHAOS field model of recent satellite data......Page 165
Field Evolution at the Earth’s Surface......Page 166
Axial dipole decay......Page 168
Evolution of integrated rate of change of vertical field at Earth’s surface......Page 170
Geomagnetic jerks......Page 171
Field Evolution at the Core Surface......Page 174
High latitude,
approximately stationary flux lobes......Page 176
Low-latitude,
westward-drifting field features......Page 177
Interpretation in Terms of Core Processes......Page 180
Maxwell’s Equations and Moving Frames......Page 181
The Induction Equation in a Spherical Earth......Page 183
The Navier-Stokes Equation......Page 185
Application of the frozen flux hypothesis to the generation of secular variation at the core surface......Page 187
Attempts to test the frozen flux approximation using geomagnetic observations......Page 188
Theoretical issues concerning the frozen flux hypothesis......Page 190
Other Invariants......Page 192
References......Page 193
5.06 Crustal Magnetism......Page 198
Glossary......Page 199
Governing Equations......Page 200
Structure of the Remainder of the Chapter......Page 201
Magnetic Petrology......Page 202
Continental and Oceanic Magnetic Anomalies......Page 203
Chicxulub......Page 204
Dike Swarms......Page 205
Heat Flux beneath the Antarctic Ice Sheet......Page 207
Compilations and Models......Page 208
Continental-Scale Compilations......Page 210
Satellite Compilations of Crustal Magnetic Fields......Page 211
Global Magnetization Models......Page 213
Removal of Noncrustal Fields......Page 214
Representations......Page 215
Transformations......Page 220
Pseudogravity......Page 221
Spatial derivatives......Page 222
Euler deconvolution......Page 223
Resolving Interpretational Ambiguity......Page 224
Spectral Overlap with Other Fields......Page 225
Separation of Induced and Remanent Magnetization......Page 228
References......Page 229
5.07 Geomagnetism......Page 239
Historical Beginnings......Page 240
Earth/ionosphere cavity......Page 241
Daily variation and Sq......Page 242
The magnetospheric ring current......Page 243
Introductory Theory......Page 244
The MT Method......Page 245
MT in Practice......Page 246
Magnetic field measurements......Page 247
MT Data Processing......Page 249
Global Response Functions......Page 250
Using magnetic satellites......Page 251
Interpretation of GDS and MT Data......Page 252
Forward Modeling in Higher Dimensions......Page 253
Numerical Inversion of Geomagnetic Data......Page 254
Electrical Conductivity of Earth Materials......Page 256
Conduction in native metals......Page 257
Ionic, or point defect,
conduction......Page 258
Binary Mixing Laws......Page 260
Textural anisotropy......Page 261
Laboratory Measurement of Conductivity......Page 262
Thermopower Measurements......Page 264
Conductivity of Mantle Minerals......Page 265
Olivine conductivity......Page 266
The Oceans and Crust......Page 269
The Mantle......Page 271
Water......Page 273
The Core......Page 274
Water in the Mantle......Page 275
References......Page 276
5.08 Magnetizations in Rocks and Minerals......Page 279
Ferromagnetism......Page 280
Antiferromagnetism and Ferrimagnetism......Page 282
Magnetocrystalline Anisotropy......Page 283
Magnetic Quantities, Units, and Conversions......Page 284
Demagnetizing Energy and Domain Structure......Page 285
Domain Wall Width and Energy......Page 287
Equilibrium Domain Structures......Page 288
Observations of Domains......Page 289
Single-Domain Grains......Page 291
Metastable SD Grains......Page 292
Pseudo-Single-Domain Grains......Page 294
Thermomagnetic Curves, Curie Temperatures, and SD Ranges......Page 296
Magnetite......Page 299
Titanomagnetites......Page 300
Maghemite and Titanomaghemites......Page 301
High-Temperature Oxidation......Page 303
Titanohematites (Hemoilmenites)......Page 304
Iron Oxyhydroxides......Page 305
Iron Sulfides......Page 306
Iron Carbonates......Page 307
Iron and Iron-Nickel......Page 308

'Magnetic’ Silicates......Page 309
SD Hysteresis and Susceptibility......Page 310
Temperature Effects: Hopkinson Peak and Koenigsberger Ratio Q......Page 313
AF Demagnetization......Page 315
Thermal Demagnetization of SD Grains......Page 317
Thermal Demagnetization of MD Grains......Page 318
Resolving Multivectorial NRM......Page 319
Thellier Paleointensity Determination......Page 320
Stability and Domain State Tests......Page 321
Thermoremanent Magnetization (TRM)......Page 322
Viscous and Thermoviscous Magnetization......Page 326
Chemical Remanent Magnetization (CRM)......Page 329
Detrital and Post-Depositional Remanent Magnetizations (DRM and PDRM)......Page 330
Summary......Page 332
References......Page 333
Introduction......Page 339
Data Types and Methods......Page 340
Geomagnetic Directional Information......Page 341
Paleointensity Data and Uncertainties......Page 342
Local and Regional Secular Variation Studies......Page 344
The KGCFS Data Compilation......Page 348
The Global Geomagnetic Field and Its Secular Variation on Millennial Timescales......Page 350
The Average Field......Page 353
Jerks, Drifts,
and Waves......Page 360
Dipole Moment Variations......Page 361
The Geomagnetic Spectrum......Page 362
Cosmogenic Isotope Production Rates - the Global View Linking Geomagnetic and Climate Studies......Page 364
Surface Exposure Dating and Local Variations......Page 366
Outstanding Problems and Scope for Future Progress......Page 367
Acknowledgment......Page 368
References......Page 369
Relevant Website......Page 374
History of the Polarity Timescale and Excursions......Page 375
Nomenclature for Excursions and Polarity Intervals......Page 377
Introduction......Page 378
The Laschamp Excursion......Page 381
The Mono Lake Excursion......Page 385
The Blake Excursion......Page 387
The Iceland Basin Excursion......Page 389
The Pringle Falls Excursion......Page 391
Excursions in the Early Brunhes Chron......Page 393
Background......Page 395
Gilsa......Page 398
Santa Rosa......Page 399
Geomagnetic Excursions in Pre-Matuyama Time......Page 400
C5n.2n (Late Miocene)......Page 402
Oligocene and Eocene......Page 403
Duration of Geomagnetic Excursions......Page 404
Excursional Field Geometry......Page 406
Concluding Remarks......Page 407
References......Page 409
Introduction......Page 419
Paleosecular Variation......Page 421
The Time-Averaged Field (TAF) - Departures from GAD?......Page 422
Paleomagnetic Observations......Page 424
Comparing data from different locations......Page 425
Measures of PSV and the TAF......Page 426
Global Field Models: Spherical Harmonic Representation......Page 428
Global Database - Paleosecular Variation from Lavas (PSVRL) Database......Page 429
Other Global Lava Flow Data Sets......Page 430
Sedimentary Records......Page 432
Paleosecular Variation......Page 433
Early PSV Models......Page 434
Giant Gaussian Process (GGP) Models......Page 435
The Time-Averaged Field......Page 436
Early Studies......Page 437
The 1990s: Longitudinal Structure in the TAF?......Page 439
Recent Studies: Joint Estimation of PSV and the TAF......Page 440
Data sets: spatial distribution......Page 441
Bias from unit vectors......Page 444
Successes and Limitations of Current TAF and PSV Models......Page 446
Toward New Global Data Sets......Page 449
A New Generation of Paleomagnetic Field Modeling......Page 450
Concluding Remarks......Page 451
References......Page 452
Introduction......Page 456
Polarity Reversals and the Geomagnetic Polarity Timescale......Page 459
Geomagnetic Intensity Fluctuations......Page 463
Anomaly Skewness and Nondipole Field......Page 470
Magnetic Source Regions......Page 471
Initial grain size and composition......Page 473
Low-temperature alteration......Page 475
Magnetization of Dikes......Page 482
Magnetization of Gabbros......Page 485
Mantle-Derived Peridotites......Page 489
Crustal Accretion and Structure of the Magnetic Source......Page 490
Nonvertical Magnetic Boundaries......Page 491
Rotations of the Magnetic Source Layer......Page 494
Future Directions......Page 496
Acknowledgments......Page 500
References......Page 501
Relevant Website......Page 508
5.13 Paleointensities......Page 509
Theory of Paleointensity......Page 510
Paleointensity with Thermal Remanence......Page 511
Linearity Assumption......Page 513
Alteration during Heating......Page 514
KTT family of experiments......Page 515
Shaw family of experiments......Page 518
Reduced number of heating steps......Page 520
Use of controlled atmospheres to reduce alteration......Page 521
Use of microwaves for thermal excitation......Page 522
Paleointensity with Depositional Remanences......Page 523
Physical Alignment of Magnetic Moments in Viscous Fluids......Page 524
Nonflocculating environments......Page 525
Flocculating environments......Page 526
PostDepositional Processes......Page 529
Normalization......Page 530
Chemical Alteration......Page 531
Depositional Remanences......Page 532
Paleomagnetic Databases......Page 533
Absolute paleointensity data......Page 534
Relative paleointensity data......Page 538
Selection Criteria from the PINT06 Database......Page 539
What is the Average Strength of the Geomagnetic Field?......Page 540
Source of scatter in the CNS......Page 542
The oldest paleointensity records......Page 543
The paleointensity
'saw-tooth’......Page 544
Sediments......Page 546
Atmospheric Interaction......Page 549
Frequecy of Intensity Fluctuations and the Climatic Connection......Page 552
Conclusions......Page 554
References......Page 555
Relevant Websites......Page 563
Planetary Moment of Inertia and the Spin-Axis......Page 564
Different Information in Different Reference Frames......Page 565
Type I TPW: Slow/Prolonged TPW......Page 566
Hypothesized Rapid or Prolonged TPW: Late Paleozoic-Mesozoic......Page 568
Hypothesized Rapid or Prolonged TPW:
'Cryogenian’-Ediacaran-Cambrian-Early Paleozoic......Page 570
Precision of TPW Magnitude and Rate Estimation......Page 571
Physical Oceanographic Effects: Sea Level and Circulation......Page 573
Chemical Oceanographic Effects: Carbon Oxidation and Burial......Page 575
Ediacaran-Cambrian TPW:
'Spinner Diagrams’ in the TPW Reference Frame......Page 578
Proof of Concept: Independent Reconstruction of Gondwanaland Using Spinner Diagrams......Page 580
Summary: Major Unresolved Issues and Future Work......Page 584
References......Page 585