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Subduction zones consume oceanic lithosphere and are an indispensible part of plate tectonics. Unlike the oceanic lithosphere production system which can be linked as a nearly continuous, albeit sinuous, strand around the earth, subduction zones are a rather dissociated group and are found in several isolated corners of the world. While plate tectonics can predict that subduction zones are required along certain plate boundaries, it does not stipulate how subduction zones initiate and develop. The preservation of newly created oceanic lithosphere and the propensity for spreading centers to fragment continents leaves a wealth of geological informa tion on the initiation and evolution of spreading. On the other hand, the subject of subduction initiation has little observational basis. To find such observations, we need to look at some muddled tectonic regimes. The Macquarie Ridge complex presents a natural laboratory for studies of subduction initiation. 2. Tectonics of the Macquarie Ridge Complex The Macquarie Ridge complex is a complicated physiographic feature that trends approximately north-south between South Island, New Zealand and the Pacific-Antarctica spreading center. This feature consists of a sequence of troughs and ridges, with Macquarie Island as the only exposed expression. The seismically active Macquarie Ridge complex (hereafter: MRC) is crudely continuous with the Tonga-Kermadec-New Zealand seismic activity. The basic physiographic features and seismicity of the MRC are shown in Figure I. The earthquake epicenters generally cluster about the bathymetric expression of the MRC.
Approximately 70 percent of the world's population is concentrated in the coastal borderlands, which geologists recognize to be the present continental margins. This new book on these continental margins provides a detailed account of a meeting which brought together specialists in marine and terrestrial geology, geochemistry, and geophysics. The workshop garnered widespread support and enthusiasm for a new direction in margins research focused on interdisciplinary studies of the fundamental processes of continental margin evolution. Scientific problems and solutions were identified for both divergent and convergent margins. Results of the workshop show that many of the fundamental plate interaction processes are common to all margins, whether formed by extension, contraction, or translation. This conclusion suggests a unified approach to margins research. A margins initiative has been proposed to follow up on the workshop results by developing science programs aimed at understanding the processes that control the initiation and evolution of continental margins.
The contributions to this book follow a topical trend. In several geophysical fields evidence is accumulating concerning the deviation of the earth's structure from radial symmetry. Seismology provides the most adequate resolution for revealing the earth's lateral inhomogeneity on a global to local scale. Lateral structure in the density distribution is also manifest in the earth's gravity field and in the geoid. Asphericity in physical parameters, generally supposed only to vary with the vertical coordinate, has a profound influence on geodynamics. The effects of these deviations from spherical symmetry concern in particular convection theory, post-glacial rebound and the dynamics of the lithosphere and upper mantle in general. At the 16th International Conference on Mathematical Geophysics which was held in Oosterbeek, the Netherlands, in 1986, the need was felt to present the state of the art. Several prospective authors were found interested to contribute to the present book. This Oosterbeek conference was one in a long series of topical conferences starting with the Upper Mantle Project Symposia on Geophysical Theory and Computers in the 1960s, and thence their successors, the conferences on Mathematical Geophysics, until the present.
In this work the central area of Corsica island was studied in order to reconstruct the tectono-metamorphic history of the continental and oceanic high pressure units that occupy the structurally deeper levels of the tectonic stacking of Alpine Corsica and their stratigraphic and structural relationship with the European margin (Hercynian Corsica). The study includes the geological mapping, the mesoscale and microscale structural analysis, the acquisition of chemical analyzes and micromaps with the microprobe, thermobarometric estimation through specific methodologies for metapelites, U-Th-Pb dating of zircons and allanites. The results obtained allows to reconstruct the geodynamic model of this sector of the Alpine belt from the Permian to the Burdigalian.
Arc-continent collision has been one of the important tectonic processes in the formation of mountain belts throughout geological time, and it continues to be so today along tectonically active plate boundaries such as those in the SW Pacific or the Caribbean. Arc-continent collision is thought to have been one of the most important process involved in the growth of the continental crust over geological time, and may also play an important role in its recycling back into the mantle via subduction. Understanding the geological processes that take place during arc-continent collision is therefore of importance for our understanding of how collisional orogens evolve and how the continental crust grows or is destroyed. Furthermore, zones of arc-continent collision are producers of much of the worlds primary economic wealth in the form of minerals, so understanding the processes that take place during these tectonic events is of importance in modeling how this mineral wealth is formed and preserved. This book brings together seventeen papers that are dedicated to the investigation of the tectonic processes that take place during arc-continent collision. It is divided into four sections that deal firstly with the main players involved in any arc-continent collision; the continental margin, the subduction zone, and finally the volcanic arc and its mineral deposits. The second section presents eight examples of arc-continent collisions that range from being currently active through to Palaeoproterozoic in age. The third section contains two papers, one that deals with the obduction of large-slab ophiolites and a second that presents a wide range of physical models of arc-continent collision. The fourth section brings everything that comes before together into a discussion of the processes of arc-continent collision.
For many years, the two subjects of (1) postglacial rebound and its potential for generating earthquakes and (2) the seismicity of passive continental ml!rgins have been of interest and concern to earth scientists on both sides of the North Atlantic. New data and theoretical interpretations have given rise to vigorous discussions on how much the two phenomena inter-relate and whether a significant controlling factor on seismicity in northeastern North America and Scandinavia is the crustal uplift that has been occurring since the latest ice age. The lack of a good understanding of these phenomena presented a particular problem for engineering seismologists attempting to prepare accurate seismic hazard estimates for facili ties both on land (e. g. , nuclear power stations and radioactive waste repositories) and offshore (e. g. , petroleum production facili ties) . The NATO Advanced Research Workshop programme provided an opportuni ty to bring together a group of relevant geophysicists, geologists and geodesists from both sides of the North Atlantic, and a workshop on "Causes and Effects of Earthquakes at Passive Margins and in Areas of Postglacial Rebound on both Sides of the North Atlantic" was held in Vordingborg, Denmark, 9-13 May 1988. The sup port of the NATO Science Committee is gratefully acknowledged.
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.
During the past 10 years, the Oil industry in India has seen a tremendous rise in exploration activity with several major E&P companies generating vast amount of new geological and geophysical data. The availability of such integrated data sets (gravity, magnetic, seismic, drilled wells), especially in the deep offshore basins, has led the authors to revisit earlier concepts and models in order to redefine the tectonic framework of major offshore basins along the Indian continental margins. The book covers the stratigraphic evolution, play types and the classification of major offshore basins both in shallow and deepwater environments. - Incorporation of latest dataset (specially the seismic, gravity and magnetic) - Analogy of global offshore basins with India - Sedimentation and depositional history of Bengal fan and Indus fan - Redefinition of major tectonic framework of the margins - Exceleent high quality graphics that include: seismic sections, gravity-magnetic maps, conceptual geological models and new revised tectonic elements