Palaeomagnetic study of Palaeoproterozoic granitoids from the Voronezh Massif, Russia

Abstract

A palaeomagnetic investigation has been carried out of rocks from the eastern part of the Voronezh Massif, which constitutes, together with the Ukrainian Shield, the Sarmatian segment in the southern part of the East European Craton. The samples were collected in a quarry close to the town of Pavlovsk (50.4°N, 40.1°E), where a syenitic-granitic body intrudes Archaean units. U-Pb (zircon) dating has yielded an age of 2080 Ma for the intrusion. Two characteristic magnetic components, A and B, were isolated by thermal and alternating-field demagnetization. Component A was obtained from granites and quartz syenites (11 samples) and has a mean direction of D = 229°, I = 28°, and a pole position at 12°N, 172°E. This pole is close to a contemporary mean pole (9°N, 187°E) for the Ukrainian Shield, which implies that the Voronezh Massif and the Shield constituted a single entity at 2.06 Ga. These poles differ from contemporaneous poles of the Fennoscandian Shield, indicating that the relative positions of the two shields were different from their present configuration about 2100 Myr ago. A component B, isolated only in quartz monzonites (five samples), has a mean direction D = 144°, I = 49°, and a pole position at 4°N, 251°E, which is close to late Sveconorwegian (approximately 900 Ma) poles for Baltica. This suggests that the East European Craton was consolidated some time between 2080 and 900 Ma. Comparison with other palaeomagnetic data permit us to narrow this time span to 1770-1340 Ma.