Properties and processes of earth's lower crust : [Collection of papers which were presented at the IUGG Symposium U 7 (Lower Crust: Properties and Processes) held in Vancouver, Canada in August, 1987

About The Product This AGU volume is a collection of papers which were presented at the IUGG Symposium U7 (Lower Crust: Properties and Processes) held in Vancouver, Canada in August, 1987. The principle objective of this symposium was to update our understanding of the properties of the lower crust and to review the physical and chemical processes which may have taken place and are still going on in the deep crust. Recent high resolution seismic experiments have thrown new light on the structure of the lower crust and crust-mantle transition which shows a much greater degree of complexity than had previously been assumed. In this symposium the complexity problem was examined from a multidisciplinary approach with papers being presented by earth scientists from the seismological, geological, geochemical, geothermal, geoelectric, geomagnetic and tectonophysics communities. A total of 38 oral and 33 poster papers were presented at the meetings. Eighteen of these papers were invited. Twenty nine of the participants have their work presented in this volume. Content: Properties and Processesof Earth's Lower Crust......Page 1 Geophysical Monograph Series......Page 2 GEOPHYSICAL MONOGRAPH SERIES......Page 3 Properties and Processes of Earth's Lower Crust......Page 5 CONTENTS......Page 7 PREFACE......Page 9 Introduction......Page 10 Geological Summary......Page 11 Seismic Data Acquisition and Processing......Page 13 Mid-crustal Velocity Increase......Page 15 Barcoo Trough......Page 16 BMR Line 1......Page 17 Sub-Moho Reflections......Page 18 Discussion......Page 19 Conclusions......Page 21 References......Page 22 Introduction......Page 24 Geological Framework......Page 25 The Layering of the Lower Crust and the Moho......Page 26 Other Seismic Events......Page 30 Constraints on the Timing......Page 32 Causes of the Layering in the Lower Crust......Page 34 Significance of the Seismic Moho andits Relation with the Upper Mantle......Page 35 References......Page 36 Comparative Geology of Newfoundland and the British Isles......Page 39 Seismic Images across Strike-Slip Faults......Page 41 Seismic Images in Overthrust Terranes......Page 42 Lower Crustal 'Wedges' and the Iapetus Suture......Page 46 Discussion......Page 47 References......Page 48 The Grenville Block......Page 50 Discussion......Page 53 Conclusion......Page 56 References......Page 57 Nevada......Page 58 Minnesota......Page 62 Discussion......Page 63 References......Page 67 Penokean Orogen......Page 69 Midcontinent Keweenawan Rift System MRS......Page 71 Results From the Grenville Front and Adjacent Terranes -Profile J......Page 72 Geometry of Structures Beneath Profile C -A North-Dipping Mega-Half-Graben......Page 75 Geometry of Structures Beneath Profile A -A South-Dipping Mega-Half-Graben......Page 77 Segmentation of the MRS......Page 78 Conclusions......Page 81 References......Page 82 Rift Basin Reflections......Page 85 Lower Crust and Moho Reflections......Page 89 Model for Rift Magmatism......Page 92 References......Page 93 Introduction......Page 94 Geology of the Area......Page 95 Previous Geophysical Work......Page 96 Experimental Results and Interpretation......Page 97 Conclusions......Page 99 References......Page 101 Introduction......Page 103 Discussion......Page 111 References......Page 117 Reflectivity Modeling of the Laminated Lower Crust......Page 120 References......Page 123 Introduction......Page 125 DSS and Other Geophysical Studies in the Area......Page 127 Crustal Velocity Functions......Page 129 Velocity Models for the Lower Crust......Page 130 Two Dimensional Travel Times Modeling......Page 131 Interpretation and Discussion of Results......Page 136 References......Page 138 Introduction......Page 140 Digitization and Presentation of the Record Sections......Page 141 Upper Crustal Model......Page 144 The Moho Boundary......Page 146 Discussion......Page 150 References......Page 153 Data Acquisition Method......Page 155 The Main Results of DSS......Page 157 Comparison of DSS Results......Page 159 References......Page 163 A SEISMIC REFRACTION STUDY OF THE CRUSTAL STRUCTURE OF THE SOUTH KENYA RIFT......Page 165 References......Page 168 SEISMICITY NEAR LAKE BOGORIA IN THE KENYA RIFT VALLEY......Page 169 References......Page 171 The Single Source-Single Station Multimode Method......Page 172 Data Processing for the Determination of Q Models......Page 175 Modeling......Page 177 Analysis of Factor R......Page 186 Conclusions......Page 188 References......Page 189 Introduction......Page 190 Tectonic Setting and Instrumentation......Page 191 Focal Depths......Page 192 Compressional Wave Velocities......Page 193 Focal Mechanisms......Page 197 Crustal Temperatures......Page 199 Discussion......Page 202 References......Page 204 Introduction......Page 207 Temperature Measurements......Page 208 Corrections......Page 209 Thermal Conductivity......Page 210 Geothermal Models......Page 211 Discussion......Page 213 Electrical Conductivity......Page 215 Seismicity......Page 221 References......Page 222 Introduction......Page 225 Conversion Technique......Page 226 D-parameter Variation with Depth......Page 227 Moho Heat Flow......Page 228 Discussion and Conclusions......Page 230 References......Page 231 Experimental Data......Page 233 Interpretation......Page 234 Discussion......Page 235 References......Page 236 Interpretation of Magnetic Anomalies in Particular Regions......Page 237 Model of the Earth's Crust as a Whole Compared with Magsat Data......Page 238 Estimations from Rock Magnetics......Page 239 Conclusions......Page 241 References......Page 242 Introduction......Page 244 Magnetization of the Crust off Canada's East Coast......Page 246 Submerged Continental Area......Page 253 Rift Basins and Ocean Continent Boundary OCB......Page 256 Oceanic Areas......Page 255 References......Page 257 Introduction......Page 260 The Method......Page 261 Results and Discussion......Page 263 References......Page 265 GRAVITY FIELD, DEEP SEISMIC SOUNDING AND NATURE OF CONTINENTAL CRUST UNDERNEATH NW HIMALAYAS......Page 267 References......Page 272 Thermal-Mechanical Models of Extension......Page 273 Extension with Distributed Magmatism......Page 274 Volume of Undernlated Material......Page 275 Metamorphism in the Lower Crust......Page 277 Rheologv and Deformation of Extensional Lower Crust......Page 278 An Example of Extensional Lower Crust......Page 279 References......Page 282 Granulites and the Lower Crust......Page 286 English River Subprovince......Page 288 Kapuskasing Uplift......Page 289 Lower Crust?......Page 291 References......Page 292 Composition and Thermodynamic Stateof the Lower Crustal Rocks......Page 296 Equilibrium Phase Diagrams......Page 298 Kinetic Model......Page 299 Lower Crust Models......Page 301 References......Page 304 Island Arc Processes......Page 306 Sediment Subduction......Page 307 Isotopic Constraints......Page 308 Delamination......Page 310 References......Page 312 Major Elements......Page 315 Rb, Sr and Their Isotopes......Page 316 Origin of Olivine Tholeiitic Magma......Page 319 Formation of Alkaline Olivine Basalt......Page 320 References......Page 322