Petrology And Geochemistry Of Continental Rifts

Proceedings of the NATO Advanced Study Institute, Oslo, Norway, July 27-August 5, 1977

This papers of this volume were invited under the general theme "Magmatism in relation to diverse tectonic settings". The work seeks to incorporate current developments in the field of magmatic activity related to collision and subduction of plates, as well as intra-plate phenomenon.

The NATO Advanced Study Institute "Paleorift Systems with Emphasis on the Permian Oslo Rift" was held at Sundvollen near Oslo, Norway, 26. July - 5. August, 1977. The meeting included 6 field trips to various parts of the Oslo Region. 70 official participants and 16 observers from 14 countries attended the meeting. The majority of the invited lectures, short research papers and progress reports presented at the meeting are published in two volumes, of which this is volume No. II. A table of con tents for both volumes is include8 herein. The field trip guide is being published in the Nor~gian Geological Survey Series, Vol. 327 (1978). We are especially pleased to acknowledge the efforts of the many authors of contributed papers, and the able assistance of secretaries, proof-readers and other staffmembers without whose help these volumes would not have been possible. Oslo, 20. February 1978. Ivar B. Ramberg Else-Ragnhild Neumann xi Organizing Committee members: O. Eldholm Department of Geology, University G. Gr¢nlie of Oslo J. Naterstad I.B. Ramberg (chairman) J.A. Dons Mineralogical-Geological Museum, B.T. Larsen (secretary) University of Oslo E.-R. Neumann (secretary) K.S. Heier (chairman) Norwegian Geological Survey S. Huseby B. Sundvoll M.A. Sellevoll Seismological Observatory, University of Bergen K. Storetvedt Geophysics Institute, University of Bergen P.M. Ihlen Geological Institute, University of Chr. Oftedahl Trondheim F.M. Vokes E.S. Husebye NTNF/NORSAR, 2007 Kjeller This volume is Scientific Report No. 40 of the Geodynamics Project.

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.

Extensive field studies on the African and North American plates during this past decade have yielded a wealth of new data and ideas about rift basins and the origin of passive margins. New surface and subsurface basins have been identified; fossils abound in strata that only recently were considered barren; oil exploration is being actively pursued in continental strata of the Richmond-Taylorsville, Sanford and Newark basins, Late Triassic marine strata have been identified in Georges Bank off the coast of Massachusetts, and the roles of wrench tectonics, successor basins and listric normal faults have challenged the classical view that these are simple extensional basins. This two part work brings together representative examples of these studies. It is not intended as an exhaustive synthesis of the subject, but rather a vehicle to present new data, new ideas and alternative views. Some of the papers present regional summaries, others attempt to relate local features to regional questions, while others describe modern rift basins as possible analogs of early Mesozoic basins. Geologic data from the Atlantic passive margins record that continental rifting of central Pangaea occurred during the latest Triassic-earliest Jurassic (Liassic), and that sea-floor spreading probably began no later than the Middle Jurassic. The primary subject of this book focuses on the Triassic-Jurassic rifting events that led to the breakup of Pangaea and the opening of the central Atlantic Ocean. Whereas other treatises have focused on the origin of the passive margins, inferred primarily from geophysical data of the offshore basins, this volume primarily and uniquely focuses on land-based field studies of the onshore synrift basins. Offshore studies of synrift basins are also included and add substantially to our understanding of the breakup. However, the onshore data base, while complementary, is different, thus providing researchers with a different insight to the questions at hand. The book is organized into four sections. Section I, Pangaean Plate in Time and Space, first locates Pangaea in space and then places the Triassic basins within an historical context on the Alleghanian-Variscan Orogens. Section 2, the offshore and onshore basins of the North American and African Plates, comprises about 70% of all papers in this book, and includes papers on structural geology, petrology, paleontology, sedimentation, organic geochemistry, vulcanism and mineral resources. Section 3, Related Mesozoic Atlantic Rift Basins, includes papers on Iberia, Western Europe, the Benue Trough and Brazil. The final section of the book, Analogs, includes the rift basins of East Africa, the Red Sea, the Gulf of Elat (Aqaba), the Dead Sea and the Rio Grande. The book is richly illustrated throughout with figures, photographs, tables and fold-out maps, including nine in full colour.

Proceedings of the NATO Advanced Study Institute, Oslo, Norway, July 27-August 5, 1977

2Gpa has increased to more than 15. This indicates that subduction of continental fragments to depths of 100-150 km may have played a significant role in the formation of mountain belts. This volume brings together the geochemical, geophysical and geodynamical approaches to study the processes active during ultrahigh-pressure (UHP) tectonics. The collection of papers demarkates the frontier of our understanding of the creation, preservation, and exhumation of ultrahigh-pressure rocks. Audience: This volume will be of interest to any earth scientist interested in ultrahigh pressure processes and the formation and modification of continental crust.