Paleomagnetic and geochronological studies on Paleoproterozoic diabase dykes of Karelia, East Finland—Key for testing the Superia supercraton

Abstract

Paleomagnetic results are presented for two Paleoproterozoic mafic dykes in the Taivalkoski area in northern Karelia Province of the Fennoscandian shield where, based on K-Ar data, the crust has seen minimal effects of the otherwise pervasive 1.8–1.9Ga Svecofennian orogeny. Within this study a new U–Pb baddeleyite age of 2339±18Ma has been determined for one of the E–W trending dykes (dyke AD13).The paleomagnetic results show that a strong Svecofennian overprinting is pervasive in the area. Upon thermal or AF demagnetization four remanence directions were obtained. Most typical are the secondary Svecofennian remanence direction A (intermediate down to the NNW) and remanence direction B (intermediate down to the NNE). Component D (D=115.4°, I=50.5°, α95=2.6°) yielding a virtual geomagnetic pole (VGP) D (Plat=−19.5°N, Plon=263.3°, A95=3.1°) is obtained from baked rocks for dyke WD, and based on a positive baked contact test is interpreted to represent the primary magnetization dating from about 2.4Ga. Dyke AD13 carries only secondary A and B components, its unbaked host migmatites carry reversed A (AR) component, and the baked host rock carries a component D′ (D=134.5°, I=−7.3°, α95=8.8°), which yields a VGP pole D′ (Plat=−20.4°N, Plon=257.3°, A95=7.6°), possibly representing magnetization at 2.3Ga.The new paleomagnetic data from the Karelia Province compared to similar-aged paleomagnetic data from the Superior Province does not support the recently proposed Superia configuration, based upon dyke swarm trajectories.