Continental Rifts Evolution Structure Tectonics

This multi-author book has been prepared by an international group of geoscientists that have been active in rift research since the late 1960s. In 1984, an informal, grass-roots study group was initiated to compare individual research results and to explore in greater depth the apparent differences and similarities in the interpretations from various rift systems. The group became known as the CREST working group, an acronym of Continental Rifts: Evolution, Structure and Tectonics, which not surprisingly became the title of this book. Continental Rifts: Evolution, Structure, Tectonics presents an overview of the present state of understanding and knowledge of the processes of continental rifting from a multidisciplinary, lithospheric scale perspective. The chapters have been structured on each rift system in approximately the same synoptic sequence, so as to facilitate comparisons of rifts by the reader. The book complements its predecessors by presenting a more unified picture. It succeeds in presenting the status of a representative majority of the continental rift systems that have been at the forefront of recent research. For students and experienced researchers alike, this book will be of significant value in assessing the current state of knowledge and in serving as a framework for future research.

This work reviews the mechanism of rifting with a focus on pre-existing tectonic weaknesses in pre-rift and/or basement rocks, i.e., on tectonic inheritance. The passive margins that are studied in this book are the Norwegian Continental Shelf, the Eastern North America and the East and West Indian Continental Margins. The continental rifts that have been analysed are the East African Rift System, the Brazilian Continental Rift Systems and the European Cenozoic Rift System. It states how rifts and passive margins serve as valuable locations for hydrocarbon exploration. Tectonic inheritance/heritage examines the influence of pre-existing/pre-rift elements on the geometry, genesis and propagation of rift-related faults. Such elements include anisotropies in the shallow crustal levels, as well as the rheology of the lithosphere. Inheritance greatly influences the architecture of rifted passive margins including the attitude of faults and geometry of horsts, (half-) grabens, transfer zones etc. Inheritance is also a determining factor in the width of rifts and rift shoulder topography.

This volume contains papers giving an interdisciplinary review of 12 major rift systems from North and South America, Africa, Europe and Asia. These papers are written by an international group of academic and industrial specialists each of whom is most knowledgeable about the respective rift. The analyzed rifts were selected on the basis of availability of an as-complete-as-possible geological and geophysical data base. Thirteen papers deal with geodynamic processes governing the evolution of rifts. A comprehensive digest of the available stratigraphic, structural, geophysical and petrological data, together with an extensive list of references, is provided for each of the analyzed rift systems. The megatectonic setting and dynamics of evolution of each basin is discussed. Geodynamic models are tested against the record of the analyzed rifts. The question of "active" as against "passive" rifting is addressed. The rifts analyzed range in age from Precambrian to Recent and cover a wide spectrum of megatectonic settings. There is discussion of the evolution of rifts in a plate-tectonic frame. The case histories are followed by discussions addressing the global setting of rifts and geodynamic processes active during the development of rifted basins.

This volume discusses the importance of rift systems and the structural evolution of the Earth. It analyses active rifts in East Africa, China and Siberia, and presents overviews of sequence stratigraphy in rifts and structural controls on clastic and carbonate sedimentation.

The ensemble of manuscripts presented in this special volume captures the stimulating cross-disciplinary dialogue from the International Symposium on Deep Structure, Composition, and Evolution of Continents, Harvard University, Cambridge, Massachusetts, 15-17 October 1997. It will provide an update on recent research developments and serve as a starting point for research of the many outstanding issues. After its formation at mid-oceanic spreading centers, oceanic lithosphere cools, thickens, and subsides, until it subducts into the deep mantle beneath convergent margins. As a result of this continuous recycling process oceanic lithosphere is typically less than 200 million years old (the global average is about 80 Myr). A comprehensive, multi-disciplinary study of continents involves a wide range of length scales: tiny rock samples and diamond inclusions may yield isotope and trace element signatures diagnostic for the formation age and evolution of (parts of) cratons, while geophysical techniques (e.g., seismic and electromagnetic imaging) constrain variations of elastic and conductive properties over length scales ranging from several to many thousand kilometers. Integrating and reconciling this information is far from trivial and, as several papers in this volume document, the relationships between, for instance, formation age and tectonic behavior on the one hand and the seismic signature, heat flow, and petrology on the other may not be uniform but may vary both within as well as between cratons. These observations complicate attempts to determine the variations of one particular observable (e.g., heat flow, lithosphere thickness) as a function of another (e.g., crustal age) on the basis of global data compilations and tectonic regionalizations. Important conclusions of the work presented here are that (1) continental deformation, for instance shortening, is not restricted to the crust but also involves the lithospheric mantle; (2) the high wavespeed part of continental lithospheric mantle is probably thinner than inferred previously from vertically travelling body waves or form global surface-wave models; and (3) the seismic signature of ancient continents is more complex than expected from a uniform relationship with crustal age.

Plate Tectonics & Crustal Evolution, Second Edition covers the role of plate tectonics in the geologic past in light of existing geologic evidence, and examples of plate reconstructions. The book discusses the important physical and chemical properties of the crust and upper mantle in terms of models for crustal origin and evolution. The text also describes sea-floor spreading; magma associations; plate tectonics and continental drift. The phanerozoic orogenic systems and the precambrian crustal development are also tackled. The book will be invaluable to students in the earth sciences and to various specialists in the geological sciences.

PERTH Western Australia March 2000 Increasingly explorationists are seeking to find new ore deposits in poorly prospected areas, be they geographically remote, such as in the Arctic, or geologically remote, such as those under sedimentary cover. Modern prospecting techniques, including low-detection-level geochemistry and the use of advanced geophysical instrumentation have greatly assisted explorers but fundamental to any soundly based exploration program remains an understanding of the geological framework of ore deposits. This allows the development of deposit models on macroscopic and mesoscopic scales. This book by Dr. Franeo Pirajno draws on his extensive and wide global experience. To set the scene for a discussion of ore deposit generation Franeo details the Earths internal structures and mantle dynamics. He then explores the impact of mantle plumes on the crust and in particular their role in the production of magmatic environments, and in continental scale rifting. This includes a descriptive section on magmatic provinces around the globe, which highlights the importance of plumes. Any study of Earth processes needs to take into account the effects of extraterrestrial bombardment, and in particular the results from the impacts of large bolides. The effects of these impacts on the atmosphere and on life have now been recognised as profound. It is likely that the effect ofthese impacts on the Earth's crust is as equally profound.