Early Proterozoic palaeomagnetism: new results from the intrusives and related rocks of the Karelian, Belomorian and Kola provinces, eastern Fennoscandian Shield

The palaeomagnetic data that are available for the eastern Fennoscandian Shield are too sparse to allow any palaeomagnetic constraints to be determined for intracratonic horizontal movements in this part of the shield. To address this issue we have obtained new palaeomagnetic data from mafic and ultramafic plutons, sills, dykes and basement country rocks in the Kola, Belomorian and Karelian provinces of the Fennoscandian Shield. A number of natural remanent magnetization (NRM) components were isolated, and we associate these with various events of Precambrian tectonomagmatic activity within the eastern Fennoscandian Shield. 36 palaeomagnetic poles were obtained. 12 poles, with ages ranging from 1700 Ma to 2450 Ma, satisfy the accepted reliability criteria (corresponding to the 'B-category' of Briden & Duff 1981). Of these, six might be classified as reference poles. For the Kola and Belomorian provinces there are poles from the Main Range gabbro-dolerites (16.7 degrees S, 304.8 degrees E, A(95) = 8.3 degrees; U-Pb age of 2436 +/- 25 Ma), the Voche-Lambina ultramafics and amphibolites (12.9 degrees N, 314.1 degrees E, A(95) = 8.6 degrees; Rb-Sr age of 2198 +/- 172 Ma), and the Kolvitsa peridotites and schists (44.2 degrees N, 232.6 degrees E, A(95) = 5.4 degrees; assigned magnetization age of 1900 Ma). For the Karelian Province, reference poles are presented for the Burakovka gabbro-norites (19.5 degrees S, 262.6 degrees E, A(95) = 7.2 degrees; Sm-Nd age of 2439 +/- 22 Ma), the Matozero doleritic dykes (20.6 degrees S, 308.5 degrees E, A(95) = 12.3 degrees; U-Pb age of 2150 +/- 60 Ma), and the Ropruchey Sill gabbro-dolerites (40.5 degrees N, 229.8 degrees E, A(95) = 8.1 degrees; U-Pb age of 1770 +/- 12 Ma). Although some NRM components of other rocks are not as precisely dated, a number of palaeomagnetic poles are in good internal agreement, forming two tracks of the Lower Proterozoic apparent polar wander path (APWP). A preliminary version of the pre-Svecofennian APWP tracks for the Karelian and Kola-Belomorian provinces is proposed. Our results confirm the general drift pattern of Fennoscandia in the Proterozoic and support the idea of the absence of large-scale block movements within the Fennoscandian Shield since Jatulian times (2300-2100 Ma). To help constrain the relative positions of the various tectonic blocks of the eastern Fennoscandian Shield during pre-Jatulian times, more new palaeomagnetic and radiometric data need to be added to the available palaeomagnetic database.