Intra-Continental Fold Belts CASE 1: West Spitsbergen

The onshore geology can provide direct access to critical rock formations and structures and is therefore able to add detail, support or modification to the story of the formation of the oceanic basins in the Arctic and North Atlantic, a story initially derived from offshore geophysical data. The project CASE (Correlation of Alpine Structural Events in Spitsbergen and Greenland) was undertaken by BGR with the intention to link onshore and offshore features in the North Atlantic region. Seismic data previously collected on a number of BGR cruises to the Labrador Sea and to the Barents and East Greenland shelves indicated mainly extensional processes in the offshore areas while, at the same time, there seemed to be a compressive fold belt developing on Spitsbergen and North Greenland. This volume contains the results of the first CASE expedition carried out in Spitsbergen in collaboration with geologists of the universities of M?nster, Erlangen and Berlin (Humboldt), Germany; Greenwich, Great Britain; and Paris (VI), France. Most of Svalbard is underlain by rocks deformed during the Paleozoic Caledonian Orogeny. But the western rim of Spitsbergen was also the site of intense crustal shortening during the so-called "Western Spitsbergen Orogeny" which, according to most authors, took place in Early Tertiary time. The resulting West Spitsbergen Fold-and-Thrust Belt is an unusual feature in that it displays spectacular fold and thrust structures but lacks any associated igneous activity and metamorphism. There are also no indications that oceanic crust is anywhere involved in the formation of the fold belt. It obviously did not form by subduction at an active margin nor by continental collision after the closure of an ocean basin. What then was the cause for the formation of this fold belt? Offshore work suggested a close association with major strike-slip movements on a dextral transform fault between North Greenland and Svalbard in the Eocene as one possible explanation. Strike-slip features, however, are not obvious in Spitsbergen. In order to test this concept of a "transpressional fold belt" the entire fold belt in Spitsbergen was investigated, from Brogger Halvoya in the north to Sorkapp in the south. Geological and structural investigations were supplemented by stratigraphic work and, where possible, also by radiometric dating. The results of this work are presented here in the form of 27 papers on various parts (northern, central and southern segment) and aspects (geology, structure, age) of this fold belt. As a result of these investigations the concept of a transpressional orogen cannot be supported because of the lack of strike-slip structures in all segments of the fold belt. On the contrary, detailed collections of structural data and general field observations both show a surprising consistency of tectonic movements to the ENE and NE, from Brogger Peninsula to Sorkapp. The structural style is not that of a flower structure but rather that of a foreland fold- and thrust belt. Based on the results from Spitsbergen, it appears that the compression of the fold belt occurred mainly before the strike- slip separation of Svalbard and the Barents shelf from Greenland. The CASE program has since been modified to the study of Circum-Arctic Structural Events, it has continued to the completion of expedition CASE 6 in 2000 and has been extended to include work in North Greenland, Ellesmere Island and Siberia. The general concept of onshore/offshore correlations, however, is unchanged.