Early Proterozoic palaeomagnetic data from the Pechenga Zone (north-west Russia) and their bearing on Early Proterozoic palaeogeography

Abstract

SUMMARY An Early Proterozoic palaeomagnetic signature (c. 2125 Ma), verified by a positive conglomerate test, is recorded in the Kuetsyarvi Formation, Pechenga Group (north-west Russia), but the majority of the palaeomagnetic directions observed in the Pechenga Group lithologies reflect a low-grade remagnetization event probably linked with the Late Precambrian Baikalian Orogeny which affected north-west Russia and northern Norway. Secondary pyrrhotite is. the dominant remanence carrier in the uppermost formations of the Pechenga Group. Palaeomagnetic poles from the Kuetsyarvi Formation differ somewhat or partially overlap with coeval palaeomagnetic poles from other tectonomagmatic provinces in northern Fennoscandia, but it is premature at this stage to speculate on intraplate movements during the Early Proterozoic. Besides, the Kuetsyarvi Formation probably developed during an early phase of intracontinental rifting along the northern margin of Fennoscandia, similar to the present-day East African rift. Hence younger intercontinental rifting, possible seafloor-spreading and subsequent convergence would remain undetected by our palaeomagnetic data. Palaeolatitude estimates from the Kuetsyarvi Formation suggest that the Pechenga region was located in latitudes of around 20 to 30 during the 2100-2200Ma interval. These low-latitude estimates are supported by the sedimentary record in the Pechenga region which is characterized by red beds and evaporites. Comparison of Fennoscandian palaeomagnetic poles with coeval poles from the Slave and Superior cratons (Laurentia) questions previously publicized supercontinental configurations. A close relationship between Fennoscandia and Early Proterozoic Laurentian Provinces is conceivable from palaeomagnetic data, but, given the lack of longitudinal control as well as the choice of hemisphere, such postulates are tentative at best on purely palaeomagnetic grounds.