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.

This article presents new and summaries of previously published geochemical and geochronological data on rocks of the Potudan pluton and host granitoids of the Kholhol-Repyevka batholith in the central part of the Don Terrane (DT) of Volga-Don orogen. The host granitoids of the Khokhol-Repyevka batholith are assigned to the Pavlovsk granitoid complex, which is widespread in the southern part of the DT. The studied Potudan pluton rocks are differentiated from quartz monzogabbro to granodiorites. They are ferroan, meta-aluminous, and the K2O content displays their relationship to the shoshonite series. For the intrusive complexes of the Don terrane, it is assumed that an enriched heterogeneous source with high contents of alkalis, LILE (large-scale lithophile elements) and LREE (light rare earth elements) is involved, the mantle component is confirmed by increased of MgO, Cr, Ni, Ti, as well as high Sr/Y ratios, (La/Yb)n, (Dy/Yb)n, indicating the deep origin of magmas. The source heterogeneity could have been provided by subduction events about 2.1 Ga. The U-Pb zircon age of crystallization of the Potudan pluton rocks (using the SHRIMP II instrument) is 2061 ± 5.4 Ma and corresponds to the postcollision event in the junction zone of the Sarmatian and Volga-Ural segments of the East European Craton. Association of Potudan rocks with Pavlovsk granitoids in time and space and also morphological features of zircon from various types of rock suites prove the effect of hybridization process during crystallization of the composite batholith. The new data make it possible to expand our understanding of the evolution of crust of the Don Terrane and geodynamic regims of its formation.

Kaalamo and Velimyaki gabbroid massifs are located in the south-eastern part of the Raahe-Ladoga suture zone of the Karelian craton and the Sveсofennian mobile belt. These massifs were formed almost simultaneously 1.89 Ga ago, occupy the same tectonic position and are located in a single unit of the Early Proterozoic metamorphosed rocks: the intrusions are contained by the Early Proterozoic supracrustal stratas: garnet-biotite gneisses and micaceous shales of the Ladoga series, as well as amphibolites of the Sortavala series. Despite this, the gabbroids of the compared massifs differ sharply in their material composition, especially the content of alkalis in a differentiated series of rocks. The results of thermodynamic modeling of magmatic crystallization (Magma Chamber Simulator, MELTS packages) showed that a differentiated sub-alkaline series of rocks of the Velimyaki massif cannot be obtained from magma of the Kaalamo massif by slightly changing such parameters as pressure, water content in the melt, and oxygen fugacity. The assumption of a significant difference in these parameters for magmas of the Kaalamo and Velimyaki massifs is not confirmed at the mineralogical-petrographic level and other characteristics of the rocks of the compared ones. The effect of contamination at the level of the magma chamber also does not significantly shift the trend of rock compositions from the calc-alkaline region to the sub-alkaline region. Analysis of the results of thermodynamic modeling of magmatic mineral formation in the two massifs allows us to make it possible to conclude that the Kaalamo and Velimyaki massifs were formed either from various parent melts, or their initial melt was one, but the magma of the Velimyaki massif underwent contamination with enrichment with alkalis along the migration route of magma until the level of the upper crust was reached.