Structural observations from the Kopperå-Riksgrense area and discussi- on of the tectonics of Stjørdalen and the N.E. Trondheim region.

Abstract

Minor tectonic structures occurring in weakly metamorphosed Hovin and Horg Group sediments along Tevedalen, east of Meråker, are described in the first part of the paper. Three episodes of folding are recognized, the respective folds showing differences in style and axial trend. First phase minor fold axes and lineations reveal a large but systematic variation of trend, generally between S.W. and N.W. The one major structure, the Teveldal syncline, is shown to have been produced during the second movement episode. Third phase structures include a penetrative cleavage axial planar to abundant minor folds whose axes trend consistently between N. and N.N.E. Thrusting of the metasedimentary pile in an E-SE direction is related to the concluding stages of the second generation of folding. The tectonics of the Stjørdalen valley area west of Meråker are then described and particular references made to the fundamental structure, a fan-anticline here called the Stjørdalen anticline. This anticline, a first generation structure, is seen to dominate the tectonic picture in the northern Trondheim region: in all probability it can be traced further south within the central part of the Trondheim \"depression\".