Major Impacts and Plate Tectonics

Book Cover......Page 1
Half-Title......Page 2
Title......Page 5
Copyright......Page 6
Dedication......Page 7
Contents......Page 8
Preface......Page 9
Acknowledgements......Page 12
1.2  Plate tectonics......Page 13
1.3.1  The lithosphere......Page 20
1.3.2  The asthenosphere......Page 21
1.3.3  Convective instability and mantle dynamics......Page 23
1.4  Factors determining plate motion......Page 25
1.4.2  Edge forces......Page 26
1.5  Tectonic evolution of terrestial planets......Page 29
1.6  Sources of impact bodies......Page 30
1.6.1  The asteroids......Page 31
1.6.2  Comets......Page 33
1.6.3  Impact flux......Page 35
1.6.4  The effects of atmosphere......Page 36
1.6.5  Summary and conclusions......Page 37
2.1  Introduction......Page 39
2.2  Characteristics of oceanic lithosphere......Page 40
2.2.1  General morphology of oceanic crust and lithosphere......Page 41
2.3  Response of lithosphere to loading......Page 46
2.3.1  Lithospheric stress......Page 47
2.3.2  Horizontal stress......Page 48
2.4.1  Over-coring......Page 49
2.4.2  Hydraulic fracture......Page 50
2.4.4  Seismic data and analysis of geological structures......Page 52
Fault movement and seismic data......Page 53
Analyses of geological structures......Page 54
2.5.1  Direction of horizontal stresses and absolute plate motions......Page 55
2.6  Rock mechanics data and the strength of the lithosphere......Page 57
2.7  Failure limits in oceanic lithosphere......Page 61
2.7.1  Stresses in oceanic lithosphere because of Gravitational Loading......Page 62
2.8  Magnitude of interplate stresses......Page 68
2.9  Conclusions......Page 71
Note......Page 73
3.1  Introduction......Page 74
3.2.1  The convection cell mechanism......Page 75
3.2.2  Driving and retarding mechanisms......Page 76
3.2.3  Spreading-ridges......Page 79
3.2.4  Subducting lithosphere......Page 80
3.2.6  Restraints caused by boundary walls and internal transform faults......Page 81
3.2.7  Critique......Page 82
3.3  Iceland, roll-over structures and gravity-glide......Page 83
3.3.1  Gravity-glide of oceanic lithosphere......Page 84
3.3.2  Restraint to slip of the low viscosity zone......Page 89
3.4.1  Anticlinal flexing of the lithosphere adjacent to the trench......Page 93
3.4.2  Intra-oceanic lithospheric fractures......Page 95
3.4.3  Elastic shortening of oceanic lithosphere......Page 97
3.5  Development of a subduction zone......Page 98
3.5.1  Off-shore basins and oceanic flexure studies......Page 99
3.5.2  Sedimentation and changes of thermal and vertical stress gradients......Page 105
3.6  Discussion and conclusions......Page 107
4.1  Introduction......Page 109
4.2.1  Continental flood basalts (CFBs)......Page 114
4.2.4  Seamount groups and submarine ridges (SMTs and SRs)......Page 115
4.3.1  Surface manifestations......Page 116
4.3.2  Plumes......Page 117
4.3.3  Modelling......Page 120
4.4  Continental flood basalts and the break-up of continents......Page 122
4.4.1  Plumes and CFBs......Page 124
4.4.2  Tomographic evidence......Page 125
(a)  Campbell and Griffith hypothesis......Page 126
(c)  Super-plumes and wet plumes......Page 127
4.4.5  Fracture-based evaluation of b required to form a graben......Page 130
4.4.6  Quantification of lithospheric thinning and enhanced melt production......Page 132
4.4.7  Development of areas of extension in continental lithosphere......Page 134
(a)  Generation or rejuvenation of strike-slip faults......Page 135
(b)  Generation of major grabens......Page 137
(a)  Thinning by chance......Page 141
(c)  Plume-induced rifting......Page 142
4.6  Conclusions......Page 146
5.1  Introduction......Page 147
5.2  The recognition of impact structures......Page 149
5.2.2  Certain craters......Page 151
5.2.3  Quantification of large impacts on Earth......Page 153
5.3  Man-made craters......Page 156
5.3.1  Geometry of real and ‘model’ craters......Page 158
5.3.2  Structures external to the crater rim......Page 164
(a)  Nose of recumbent fold......Page 165
(c)  Peripheral folds......Page 166
(d)  Radiating vertical fractures......Page 167
(d)  Thrusts......Page 168
5.3.3  Correlation between experimental and real impact structures......Page 170
5.3.4  Small-scale and microscopic structures......Page 171
5.3.5  Geophysical techniques......Page 173
5.4  Moon v. Earth......Page 175
5.4.1  Moon-like circular assemblages on Earth......Page 176
5.5.1  Compressive and tensile stress-waves......Page 178
5.5.2  Computer models......Page 182
5.5.3  Fractures and folds external to the crater......Page 183
5.5.4  Gradation from simple to central, or ringed, uplift craters......Page 186
5.5.5  Size of craters and the energy of the impact event......Page 187
Energy of impact, crater diameter and volume of melt......Page 188
5.5.6  Asteroids or comets?......Page 190
Shotgun model......Page 195
5.6  Summary, conclusions and inference......Page 196
6.1  Introduction......Page 199
6.2  The Atlas system......Page 200
6.3.1  Tracks associated with known or inferred impact events......Page 203
6.3.2  Continental flood basalts......Page 206
(a)  Columbia River flood basalts......Page 207
(b)  Afar plateau basalt (or Arabia-Ethiopia-Africa plateau basalt)......Page 208
(c)  Deccan Traps......Page 210
(d)  Paraña......Page 211
(g)  Karoo, S Africa......Page 212
(h)  Siberian flood basalt......Page 213
6.4  Oceanic basalts—the Ontong-Java event......Page 214
6.6.1  Hypothetical impact model......Page 219
6.6.2  Tomographic evidence......Page 222
6.7  Cratering and the development of oceanic and continental basalts......Page 223
6.7.1  Effect of lithospheric thickness on oceanic and continental PBs......Page 227
6.8  The splitting of continents......Page 229
6.8.1  Opening of the S Atlantic......Page 230
6.8.2  Original relationships of landmasses adjacent to the ‘S Atlantic’......Page 231
6.9  Summary and conclusion......Page 240
7.1  Introduction......Page 242
7.2  ‘Conventional’ development of arcuate oceanic trenches......Page 243
7.3  Mid-ocean trenches which form arcs of a circle......Page 245
7.4  The Scotia arc......Page 246
7.4.1  Mechanisms......Page 251
7.4.2  Subduction along a semicircular trough......Page 257
7.4.3  Timing and evidence of the impact event......Page 258
7.5  The Caribbean (or Lesser Antilles) Arc......Page 259
7.5.1  The impact event......Page 262
7.6  The Banda Arc......Page 263
7.7  The Amirante Arc......Page 266
7.7.1  Tracks......Page 268
7.8  The Mariana Trench......Page 270
7.9  Impact size and minor subduction arcs......Page 272
7.9.1  Rock failure in terms of pulse and ambient stresses......Page 273
7.10  Impact of comet-bodies in deep ocean......Page 277
7.10.1  Comets and comet-derived bodies......Page 278
7.12  Summary and conclusions......Page 282
8.1  Introduction......Page 284
8.2  Periodicity and relationship of cyclical events......Page 285
8.2.1  Galactic control of periodic events of Earth?......Page 286
8.2.2  The environmental effects of impacts......Page 291
8.3  More tracks......Page 294
8.3.1  Details of tracks from seven localities......Page 295
Hawaii......Page 296
Borneo......Page 297
Japan......Page 298
N America......Page 299
Mariana......Page 301
8.4  Peridocity and impact-flux changes in the Phanerozoic......Page 305
8.4.1  Correlation between impacts and other events in the Lower Phanerozoic......Page 308
8.4.2  Impact flux in the Lower Phanerozoic......Page 311
8.5  Impacts, a hazard to humanity......Page 314
8.5.1  Comment and conjecture relating to impact flux......Page 316
8.6  Synopsis......Page 318
Appendix......Page 322
References......Page 325
Index......Page 342