Late Orogenic Granitoids of the Tervu Agmatitic Zone in the Southeastern Part of the Svecofennian Belt (Northern Ladoga Area, Russia)

Abstract

The Tervu breccia zone was formed at the final stages of the Late Proterozoic magmatic and metamorphic activity (1.86 Ga ago) and healed with granitic material shortly after its formation. The Tervu breccia zone with granitic agmatites has a sublatitudinal orientation, which is discordant in relation to the earlier structures and Kurkijoki enderbite and Lauvatsaar–Impiniem diorite–tonalite complexes in the Svecofennian rocks of the Ladoga region. The largest granitic bodies in this area, the Tervu and Peltola intrusions, are located in the Tervu Zone. The U–Pb age of monazite from granites of the Peltola intrusion is determined as 1859 ± 4 Ma and coincides with the age of the granites of the Tervu intrusion (1859 ± 3 Ma), which indicates that the granites of both intrusions and some surrounding smaller bodies were intruded simultaneously into the tectonically weakened space at the late-orogenic stage while plastic deformations were turning to elasto-plastic ones. The results obtained reveal the features of the tectonic development of the junction zone of the two largest blocks of the Fennoscandinavian shield, the Karelian Craton and the Svecofennian Belt.