Evolution of the Caledonides in the northern Trondheim region, Central Norway: a review

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Abstract
Summary: A résumé of the stratigraphy, sedimentation and volcanism of the Lower Palaeozoic rocks in the northern Trondheim region is presented. Spatially the Caledonian rocks occupy a shallow trough which plunges south-west. Within the trough the rocks have been subject to four episodes of deformation; the essential structure of the region is an anticline flanked by recumbent fold nappes (F1) which spill outwards on either side of the NE-trending spine. These are deformed by further major folds (F2). The F3 folds, developed widely but only on a mesoscopic scale, show a constant down-dip sense of overturning. It is thought that they were formed in response to gravitational sliding. F4 is represented only by local kink bands. It is probable that large areas of these Cambro-Silurian rocks are allochthonous, the marginal thrust being of late-F2 age. Examination of the structures is illuminating many other aspects of the geology of this segment of the Caledonian chain, making it possible to visualize the changing sequences of deformation, the relationship of metamorphism to tectonic level and the tectonic behaviour of domal granitic masses. In conclusion, comments are made on the relative significance of the orogenic ‘disturbances’ described from this part of Norway.

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