OROGEN-PARALLEL TRANSPORT AND VERTICAL PARTITIONING OF STRAIN DURING OBLIQUE COLLISION, EFJORDEN, NORTH NORWAY

Thrust sheets in the Caledonian allochthon in northern Scandinavia wer e emplaced generally toward the ESE, an orientation nearly perpendicul ar to the trend of the Caledonian orogen. In the Efjord area of north Norway, however, orogenesis also produced top-to-the-SSW motion on N-d ipping thrust faults in the cratonal basement beneath the allochthon. The leading edges of some SSW-directed thrust-sheets moved upward into the overlying metasedimentary cover and formed the cores of S-verging recumbent fold-nappes at the base of the Caledonian allochthon. As de formation continued, these fold nappes became entrained in the top-to- the-ESE transport of the overlying allochthon. Mutually cross-cutting relationships suggest contemporaneous SSW-directed thrusting in the cr atonal basement and top-to-the-ESE movement of the allochthon. Thus, s tructures in the Efjord study area reflect vertical partitioning of st rain into components with nearly orthogonal displacement directions at different structural levels. Collectively, the top-to-the-SSW (orogen -parallel) and top-to-the-ESE (orogen perpendicular) components of tra nsport are consistent with overall sinistral-oblique, post-collisional convergence between Baltica and Laurentia. Implications include: (1) in some parts of the orogen, recumbent folds with hinges sub-parallel to the transport direction of the allochthon were produced by orogen-p arallel transport rather than orogen perpendicular sheath-folding; and (2) orogen-parallel components of structural transport make two-dimen sional palinspastic restoration in planes perpendicular to the orogen difficult or inappropriate in some locations. Copyright (C) 1996 Elsev ier Science Ltd.