Extract

The area studied (Fig. 1) lies in the Caledonides of northern Norway, and consists of a sequence of nappes emplaced on to Baltica during the mid- to end Silurian, Scandian phase (Gee 1975) of the Caledonian orogeny. These largely metasedimentary nappes locally contain thick amphibolite units, whilst synorogenic ‘granitoid’ bodies are widespread in some of the higher nappes.

The geological history of the region has been established following the work of Gustavson (1966, 1974) and Barker (1986). Initial D₁ and D₂ deformation gave rise to recumbent isoclinal folds. A pervasive regional schistosity (S₂) developed in association with F₂, by transposition of S₁. The only evidence for the earlier fabric is as inclusion trails within porphyroblasts. Although affected by later folding, S₂ is mostly subhorizontal, and rarely dips at more than 30°. The orientation and attitude of early folds, coupled with the pronounced northwest-southeast-trending L₂ stretching lineaton, indicate that the main transport direction was towards the south-east. Additionally, the attitude of well-developed C′-fabrics (Platt 1984) in phyllonites of the Fossbakken Nappe (Fig. 1) also indicate this sense of movement. The D₃ structures evolved progressively from early recumbent isoclines to later open more upright folds. During D₄, upright open F₄ structures developed mostly northnortheast-southsouth-west-trending axes. Crenulations and small folds are dominant, but larger structures such as the Ofoten synform (Gustavson 1974) also formed (see Fig. 1). Peak metamorphism occurred just prior to, and synchronous with the development of the regional (S₂) schistosity, whilst nappe assembly occurred from late D₂ and through D₃. Isograds associated with peak metamorphism became truncated, as higher