Superposed folding and metamorphism in the Seve nappe around Åreskutan in the Swedish Caledonides

Abstract

The earliest recognisable folds (F₁) in the Seve nappe in the Åre area in the central Swedish Caledonides include a phase of co-axial refolding (F_1A and F_1B). These isoclinal, tight reclined or recumbent folds are parallel to the principal mineral lineation and mylonitic striation. There is a set of tight, reclined folds (F₂) which refold the mineral lineation and F₁ hinges at large angles. The open F₃ folds refold the F₂ hinges at small angles. In addition to the above structures, there is also a set of open, upright folds (F₁) with axes parallel to the mineral lineation (and to F₁) which is younger than F₁. The time-relation of these F₁ folds to the F₂ folds is not clear. The field evidence indicates that F_1B and later folds have developed during different stages of thrusting. The period of migmatization and high-grade metamorphism within the nappe has overlapped with the period of development of the F₁ and F₂ structures.