Syn-collisional extension in the North Atlantic Caledonides

High-grade metamorphic rocks are commonly found in the interior of many convergent orogens. Plate tectonic processes can account for high- and ultra pressure (HP &UHP) metamorphism by subduction and crustal thickening, but the processes involved in the re turn of these metamorphosed crustal rocks back to the surface is less well understood. Both thrust faulting combined with erosion, extensional fault, ductile thinning, and erosion may contribute to the exhumation process. In the Scandinavian and E Greenland Caledonides late- to post-orogenic extensional faulting has been called upon as the most likely mechanism for exhumation of high pressure rocks. The temporal and spatial relationship between contractional and extensiona l deformation in the two segments of the orogen is however far from clear. Data from the Scandinavian Caledonides indicates that exetension responsible exhumation of HP-rocks is post-collisional, whereas extension in E Greenland appears to be syn-collisio nal. To critically test the hypothesis of syn-collisional extension in E Greenland, implying vertical strain partitioning, we plan to carry out combined structural and geochronological investigations in areas representing different crustal levels. Project part icipants (post-doc and several graduate students) will also study the age and exhumation of HP-rocks in the Caledonides of North Norway and Svalbard.