Collisional Orogeny in the Scandinavian Caledonides (COSC)

Abstract

The COSC project is focused on the mid Paleozoic Caledonide Orogen in Scandinavia in order to better understand orogenic processes, both in the past and in today's active mountain belts. It relates to two of ICDP's main themes – the fundamental physics of plate tectonics and heat, mass and fluid transfer through Earth's crust, and on improving interpretation of geophysical data used to determine the structure and properties of the Earth's crust. Lateral transport of Caledonian allochthons over distances of several hundreds of kilometers in the Scandes, by a combination of thrusting and ductile extrusion, is comparable to that recognized in the Himalayas. The Caledonides in Scandinavia provide special opportunities for understanding Himalayan-type orogeny and the Himalayan Orogen itself, thanks to the deep level of erosion and the paucity of superimposed post-Paleozoic deformation. The surface geology in combination with the seismic, magnetotelluric, magnetic and gravity data provide control of the geometry of the Caledonian structure, both of the allochthon and the underlying parautochthon-autochthon, and define the locations for drilling. The latter will investigate both the high-grade, ductile Caledonian nappes and the underlying allochthons and basement, with two c. 2.5 km deep boreholes, located near Åre and Järpen in western Jämtland. The two boreholes will also provide unique information about other important aspects of the Scandinavian bedrock, including the heat flow and potential for geothermal energy, mineralization in the Seve nappes and alum shales, the uplift history of the Scandes, the Holocene paleoclimatological changes and the deep biosphere.

Keywords:

• Swedish Deep Drilling Programme
• geology/geophysics
• Caledonide Orogen
• Seve ductile extrusion
• structure
• metamorphism
• geochronology
• reflection seismics
• heat-flow
• geothermal energy

Acknowledgements

We thank Dan Dyrelius and Laust Pedersen for contributing to the section on geophysics, Elena Kashubina for coordinating the preparation of the manuscript, Nina Lebedeva-Ivanova for drafting the diagrams and David Roberts for comments on an early edition of the text. The manuscript has also benefitted from helpful reviews by Per-Gunnar Andréasson and Håkan Sjöström.