The Caledonian mountain chain of the Southern Troms and Ofoten areas. Part III. Structures and structural history.

Abstract

The main lines of the structural geology of the area of about 13,000 km\u00B2 in the Caledonian mountain chain of Northern Norway are described. The major structure is characterized by nappes with a thrust front in the east above authochthonous Precambrian basement and Lower Cambrian sediments. The discovery of basal-type psammitic rocks in the westernmost part of the area strengthens the opinion that the basal gneisses to the south and west of the Caledonian nappes consitute Precambrian basement. The basement took part in extensive folding and thrusting during the main Caledonian orogeny, but mobilization features are absent. The structural history can be summarized as follows: Early epeirogenic movements are indicated be the Elvenes (-Harstad-Evenskjær) conglomerate zone. The main Caledonian deformation commenced with an episode of isoclinal folding, F1 (in eastern areas an even earlier episode of isoclinal folding has been recognized by other workers), with an associated axial plane schistosity. Later deformation episodes produced open to tight folds but usually without the development of a new axial plane schistosity. Thrusting occurred during and after the first fold episode.