We present the first 1.86 Ga paleomagnetic key pole of Fennoscandia obtained for the dolerite sills of the Murmansk craton - Eastern Murman Sill Province, that outcrop in the northern part of the Kola Peninsula along the Barents Sea coast for a distance of 200 km (Slat = 68.5 degrees; Slong = 37.9 degrees; N = 16 sites; Plat = 54.7 degrees; Plong = 234.7 degrees; dp/dm = 4.3 degrees/6.3 degrees, Qv = 5). The age of the sills and their characteristic remanent magnetization (ChRM) was determined by four independent geochronometers: U-Pb -1860 +/- 4 and 1863 +/- 7 Ma (IDTIMS, baddeleyite), Sm-Nd - 1889 +/- 57 Ma, Rb-Sr - 1850 Ma, Ar/Ar - 1865 +/- 8 and 1857 +/- 20 Ma (biotite). The primary nature of the ChRM is confirmed by the results of petrographic, geochemical, paleo- and rock magnetic studies, as well as by thermochronological data. The similarity of the petrographic and geochemical characteristics of sills from different localities indicates that these dolerite sills were formed during a single magmatic event and their cooling down to 580 degrees C occurred at depths of about 10 +/- 2 km and lasted similar to 2800 years or even faster. Paleogeographic reconstruction of Fennoscandia on the basis of the obtained paleomagnetic pole is in general agreement with the previously suggested configuration of core of the Nuna/Columbia supercontinent (Evans and Mitchell, 2011; Meert and Santosh, 2017). A new reliable Thellier-Coe paleointensity determination for this time reveals a rather low mean VDM = 1.8 ( +/- 0.1) x 10(22) Am-2 that supports the Proterozoic dipole low hypothesis (Biggin et al., 2009).
Scopus subject areas
- Geochemistry and Petrology