Complete remagnetization of some Permian dykes from western Norway induced during burial/uplift

Abstract

Stable paleomagnetic directions in four basaltic dykes and in some associated Caledonian metamorphic rocks define high-latitude, Mesozoic paleomagnetic pole positions which are not compatible with the KAr age of ∼250 My determined for the dykes. A monotonic increase of ∼40% occurs in the potassium content of samples taken across a dyke 32 cm wide. This is accompanied by only a 1–2% variation in the KAr age of the samples, suggesting the absence of any significant level of initial argon. Titanomagnetite grains having bulk compositions around x = 0.6 have suffered extensive low-temperature alteration, forming assemblages of ferri-rutile granules in a matrix of pure magnetite. The complete remagnetisation of both the dykes and the associated country rocks is probably an expression of a VRM acquired at elevated temperatures (150–500°C) at the emplacement depth of the dykes. A stable remanent magnetisation was locked-in during uplift of the area, probably related to the Kimmerian basin development in the adjacent North Sea and the epeirogenic uplift of western Fennoscandia.