Continental Lower Crust

About this book

This is a multi-disciplinary review of the current state of geological and geophysical research on the continental lower crust. Topics include the structure of the crust as deduced from geophysical research, rheology of the lower crust, composition and evolution of the lower crust as constrained by xenoliths, magmas, crustal cross-sections, the role of fluids in the crust, and the interaction of the lower crust and magmas. Each chapter has extensive reference lists. The audience for this book is diverse. One group will consist of newcomers (students and professionals) to lower crustal research who are looking for an overview of the current research. For this group, the present volume can serve as a point of departure for further investigation of the continental lower crust. A second audience will consist of active researchers interested in reviews of aspects of lower crustal researchers out of their discipline. These scientists will find that the synoptic view presented within this volume opens new avenues of research. The book is appropriate for use in graduate-level seminars dealing with various aspects of continental structure and evolution.

Contents

Preface. List of Contributors. Symbols. 1. The Seismic Velocity Structure of the Deep Continental Crust (W.S. Holbrook, W.D. Mooney and N.I. Christensen). Wide-angle seismic data. Middle- and lower-crustal velocities. Seismic velocities: constraints on composition. Fluids and anisotropy. Discussion. 2. Multi-Genetic Origin of Crustal Reflectivity: A Review of Seismic Reflection Profiling of the Continental Lower Crust and Moho. (W.D. Mooney and R. Meissner). The seismic reflection method. Observations of the continental lower crust and Moho. Multi-genetic origin of lower crustal reflections. Reflectivity and viscosity in the lower crust. 3. Electrical Properties of the Lower Continental Crust (A. Jones). Review of methods. Summary of results. Causes of enhanced electrical conductivity in the continental lower crust. 4. Magnetic Properties of the Lower Continental Crust (P.N. Shive et al.). Long-wavelength magnetic anomalies. Magnetic properties of lower crustal rocks. Nature of magnetic bodies in the lower crust. 5. Thermal State of the Continental Crust (D.S. Chapman and K.P. Furlong). Geotherm models. Thermophysical parameters. Framework geotherms. Processes and conditions that affect or modify the thermal state of the continental lower crust. Crustal heterogeneities. 6. Rheology of the Lower Crust (E.H. Rutter and K.H. Brodie). Deformation mechanisms. Data from experimental rock mechanics. Localization of strain into shear zones. The size of recrystallized grains. Structures and microstructures of naturally deformed rocks. Flexure of the continental lithosphere. 7. Xenoliths - Samples of the Lower Continental Crust (R.L. Rudnick). The samples. Effects of transport. Mineralogy. P-T estimates. Physical properties. Chemical composition. Isotopic studies. Case studies. A lower crustal composition from xenoliths. Representativeness of xenoliths as lower crust. 8. Exposed Crustal Cross Sections as Windows on the Lower Crust (J.A. Percival, D.M. Fountain and M.H. Salisbury). Compressional uplifts. Wide, oblique transitions. Impactogenic uplifts. Transpressional uplifts. Characteristics of lower crust in cross sections. Implications for the nature of the lower crust. 9. Magmas as Tracers of Lower Crustal Composition: An Isotopic Approach (G.L. Farmer). General technique. Case example - Western U.S. Other examples. 10. Fluids in the Deep Crust - Petrological and Isotopic Evidence (S.M. Wickham). Equilibrium thermodynamic calculations. Fluid inclusions. Stable isotope constraints on deep crustal fluids. Melting and fluid transport. 11. Magma Genesis and Crustal Processing (R.W. Kay, S. Mahlburg Kay and R.J. Arculus). Magmas in the crust: processes and models. Magmatic underplanting. Anatexis and granitoid melt generation. Continental growth, recycling and the lower crust. 12. Temporal Evolution of Regional Granulite Terranes: Implications for the Formation of Lowermost Continental Crust (K. Mezger). Characteristics of regional granulite terranes.

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