The structure of the Magerøy Nappe, Finnmark, North Norway.

Abstract

The Magerøy Nappe was emplaced during the Scandinavian phase of the Caledonian orogeny, of Middle\/Upper Silurian age. Two main episodes of deformation (D1 and D2) with attendant Barrovian-type regional metamorphism are recorded in the metasediments of Upper Ordovician\/Lower Silurian age forming the Magerøy Supergroup (minimum thickness 5,5 km). The D1 deformation produced overturned to recumbent regional folds which due to opposite vergence from a mushroom-like culmination in central Magerøy. D1 folds east of the structural divergence zone are tight, recumbent folds with eastward vergence, while those to the west are overturned asymmetrical folds verging to the west. Textural and structural observations indicate that D1 consisted of two deformational events(D1a and D1b) of which the later coincides with the final movements along the basal thrust of the nappe. The metamorphism reached its peak in the period between d1 and D2, and was accompanied by acid and mafic\/ultramafic intrusions (417\u00B111 m.y., Finnvik Granite). D2 which occurred under retrograde metamorphism, produced a large synformal structure, essentially coaxial with the F1 folds, but with a subvertical axial surface. In the structural depression along the axial trace of this fold the highest structural levels of the Magerøy Nappe mushroom-structure, and an erosional klippe of a higher nappe, the Skarsvåg Nappe, are preserved. The F2 folding of Magerøy is correlated with the late, large-scale buckling of the Finnmarkian phase nappes of the mainland in West Finnmark.