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Collisional Orogeny in the Scandinavian Caledonides (COSC)



The COSC project focuses 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.
As seen in the geophysical interpretations of the young orogens today, plate collision and the resulting contraction leads to doubling, even trebling of the thickness of continental crust, forming mountain belts with high relief. In the older orogens, the record of crustal thickening and inferred high relief is preserved in the high pressure mineralogy of the metamorphic rocks (e.g. eclogites, with coesite and diamonds) deep in the hinterland and also in some long-transported allochthons.
The Scandinavian Caledonides provide a particularly well preserved example of Paleozoic plate collision, with the underthrusting of continent Baltica beneath Laurentia and thickening of the continental crust to at least 100 km. In the Scandes, the surface geology in combination with geophysical data provide control of the geometry of the Caledonian structure, both of the allochthon and the underlying parautochthon-autochthon, and define the targets for drilling. The drillholes themselves will help us to better define the structure and physical conditions of the allochthons and underlying parautochthon during nappe emplacement.

Lateral transport of 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 unique opportunities for understanding Himalayan-type orogeny and the Himalayan Orogen itself, thanks to the deep level of erosion (mid to lower crustal) and the paucity of superimposed post-Paleozoic deformation. In the Himalayas, an understanding of the on-going India-Asia collision at depth in the hinterland is primarily dependent on interpretation of geophysical data (seismic, potential field, geothermal and GPS) and analysis of magma signatures. By contrast, in the Scandes, it is possible to directly observe the "fossilized" Paleozoic collisional processes that occurred in the middle and lower crust, from the foreland far into the hinterland, over a distance across the orogen of c. 300 km.

Existing seismic and magnetotelluric data image the geometry of the upper crust in the central Scandes (Östersund-Trondheim) profile, with a well defined shallow W-dipping décollement surface on a thin skin of Cambrian black shales beneath the Caledonian thrust sheets. The structure of the basement underneath the décollement is highly reflective and apparently dominated by mafic sheets intruded into either late Paleoproterozoic granites or Mesoproterozoic volcanics and sandstones. This project targets both the Caledonian nappes ("hot" allochthon) and the underlying basement, with two c. 2.5 km drillholes, located near Ĺre and Järpen in western Jämtland.

In addition to the focus on orogen dynamics, the proposed drillholes will provide unique information about the present temperature gradient in the Caledonides, the porosity and permeability of the rock formations, and the petrophysical properties of the rocks at depth. If porosity and permeability are found to be adequate these boreholes will promote interest in the bedrock in Jämtland for geothermal energy extraction and also for geological storage of CO2 (for example, in connection with the mining of alum shales and other mineral resources). In addition, the project will study the deep biosphere and the Cenozoic uplift history of the mountain belt.



Europe, Scandinavian Caledonides, Sweden, Are, Jarpen



63° 24' 6'' N, 13° 12' 11'' E (Please scroll down to end of page for more information.)


Project Start and End
  • start of drilling planned for April/May 2014


Programs and Funding


Principal Investigators
  • Christopher Juhlin, Uppsala University, Department of Earth Sciences, Geophysics
  • David G. Gee, Uppsala University, Department of Earth Sciences, Geophysics
  • Randall Parrish, British Geological Survey, Natural Environment Research Council
  • Christophe Pascal, Ruhr-University Bochum, Institute of Geology, Mineralogy and Geophysics, Endogenous Geology
  • Chinfu Tsang, Lawrence Berkeley National Laboratory, Earth Sciences Division
  • Karsten Pedersen, Microbial Analytics Sweden AB


Partners and Contractors



Caledonides, COSC, Deep Hydrosphere, Dynamics, Europe, Heat Flow, Himalaya, ICDP-2011/03, Microbiology, Norway, Orogen, Scandes, Scandinavia, Seismic, Sweden


Current State





    Google Earth/Maps