Palaeomagnetism of the Ragunda intrusion and dolerite dykes, central Sweden

Abstract

Abstract The large Ragunda intrusion (1320 Ma) and dolerite dykes cutting the intrusion near its western margin have been extensively sampled for palaeomagnetic study. After comprehensive alternating field and thermal demagnetisation, the intrusion yields a mean direction D = 20°, I= 46° (α95 = 7°); both polarities are present. Two stages of dyke intrusion are identified from their magnetisations: a small number of dykes have directions similar to the Ragunda intrusion and the remainder yield a mean D = 182°, 7=24° (α95= 14°); both polarities are present in each case and neither dyke suite correlates with the magnetisations of post-Jotnian (ca. 1200 Ma) dolerites from elsewhere in the Fennoscandian Shield. Magnetisations reside in different phases of titanomagnetite, pyrrhotite is a locally important remanence carrier, but maghemite, although sometimes present, has not been identified as a significant carrier. The palaeomagnetic poles help to clarify the form of the apparent polar wander path for the Fenn...