A late Paleoproterozoic key pole for the Fennoscandian Shield: A paleomagnetic study of the Keuruu diabase dykes, Central Finland

Abstract

We present an updated paleomagnetic pole and a new isotope age for the late Paleoproterozoic (Svecofennian) diabase dykes from Keuruu, Central Finland. The paleomagnetic results reveal a dual-polarity remanent magnetization with asymmetry, which we explain by an unremoved secondary component contaminating both normal (N) and reversed (R) vectors. The ChRM is carried by magnetite, most of which are primary grains crystallized from basaltic magma. The primary nature of the ChRM is further supported by positive baked contact tests. An R polarity dyke shows a U-Pb concordia age of 1870±9Ma. Zircons from another dyke of N polarity reveal a mean Pb-Pb age of 1867±8Ma. The combined N and R mean ChRM direction is D=340.4°, I=35.2°, α95=5.8°, k=31.3, N=21 dykes (yielding a paleomagnetic pole of Plat=45.7°, Plon=230.9°, A95=5.5°. This positions the Fennoscandian Shield at low latitudes (19.4°), and aligns with Superior Craton in a way that would naturally proceed into the 1.8–1.2Ga NENA (North Europe–North America) configuration. Paleosecular variation analysis of N polarity dykes is consistent with the low latitude position of Baltica.