Geomagnetism in Marine Geology (eBook)

Front Cover 1
Geomagnetism in Marine Geology 4
Copyright Page 5
CONTENTS 8
PREFACE 6
CHAPTER 1. THE PHYSICS OF GEOMAGNETISM 12
Magnetic intensity 12
Intensity of magnetization 13
Field due to a dipole 13
Inclination of the geomagnetic field 16
A simple two-dimensional model for rough estimates 17
CHAPTER 2. MAGNETIC PROPERTIES OF OCEANIC BASALTS 22
Diamagnetism and paramagnetism 22
Ferromagnetism 22
Anti-ferromagnetism and ferrimagnetism 24
Composition of ferromagnetic rock-forming minerals 25
Effects of domain and grain size 27
Thermoremanent magnetization 29
Thermomagnetic properties of oceanic basalts 31
Removal of unstable magnetization 32
Magnetic viscosity 33
Natural magnetization of basalts 34
Instruments and methods for measuring magnetic properties 35
CHAPTER 3. MEASUREMENT OF GEOMAGNETIC INTENSITY AT SEA 38
The total intensity anomaly 38
The proton magnetometer 39
CHAPTER 4. THE EARTH’S MAGNETISM AND ITS HISTORY 42
The elements of the geomagnetic field 42
Time fluctuations 43
Secular variations 45
Chronology of geomagnetic field reversals 48
The theory of Vine and Matthews 49
Reversal chronology in ocean sediments 52
Extrapolation of reversal chronology from lineated anomalies 55
Length of polarity epochs 61
The geomagnetic dynamo 62
CHAPTER 5. EXAMPLES OF LINEATED MAGNETIC ANOMALIES IN THE OCEANS 64
Identification of lineated anomalies 64
Subjectivity of the comparison process 65
Test for symmetry 67
The Antarctic Pacific 68
The South Atlantic 72
CHAPTER 6. UNDERTHRUSTING OF THE LITHOSPHERE AND PLATE TECTONICS 76
Model of spreading and consumption of lithosphere 77
Foci of earthquakes 78
Other evidence for consumption 79
Transform faults and epicenters 83
Earthquakes outline tectonic plates 85
Plate rotations 86
Examples of plate rotations 88
CHAPTER 7. ABSOLUTE DISPLACEMENT WITH REGARD TO THE EARTH’S ROTATIONAL AXIS 93
Paleomagnetism of seamounts 93
Calculation of virtual geomagnetic poles 96
The polar curve 97
Northward drift of the Pacific Plate 98
Latitude from magnetization of sediments 101
Paleolatitude from anomaly shape and amplitude 102
The biogenic equator 104
CHAPTER 8. INTERACTION BETWEEN THE FLOOR OF THE PACIFIC OCEAN AND ITS MARGINS 107
Subduction in Aleutian Trench 107
Origin of the Great Magnetic Bight 108
Shifting of spreading direction in the Northeast Pacific 109
CHAPTER 9. THE INDIAN OCEAN 117
Coverage 117
Two spreading episodes 118
Identification of older anomalies 120
Evolution of the Indian Ocean floor 124
CHAPTER 10. DEPENDENCE OF OCEAN DEPTH AND TERRESTRIAL HEAT FLOW ON THE AGE OF THE OCEAN FLOOR 127
Cooling after extrusion 127
Measurement of heat flow at sea 127
Age bands in the northern Pacific 127
Continental heat flow 127
Crustal model 130
Calculation of ocean depth from age 130
CHAPTER 11. THE NORTH ATLANTIC 135
Four magnetic zones 135
Variable spreading rates 138
Variations in spreading direction 144
Rotation of Spain 145
Greenland and the Labrador Sea 146
A single supercontinent 146
CHAPTER 12. THE ARCTIC OCEAN 151
From Iceland to Nansen Ridge 151
The Nansen Ridge 154
CHAPTER 13. MAGNETIC INTENSITY MEASUREMENTS NEAR AND ON THE BOTTOM 159
Near bottom magnetic surveys 159
Magnetic short-time variations on the ocean floor 162
CHAPTER 14. POSSIBLE FUTURE DEVELOPMENTS 167
APPENDIX 1. INTERNATIONAL GEOMAGNETIC REFERENCE FIELD 1965.0 169
APPENDIX 2. CALCULATION OF TOTAL MAGNETIC INTENSITY PROFILE PERPENDICULAR TO A RIDGE MODEL 171
APPENDIX 3 . MAGNETIC PROPERTIES OF OCEANIC BASALTS 177
REFERENCES 183
INDEX 191