Shvaika I. The Paleoarchean age and the dislocation stages of the tonalite gneisses of the Western Pryazovia (Ukrainian Shield)

The strongly dislocated outcrops of the Paleoarchean tonalite gneisses (3560±70 Ma) ware observed in the upper reaches of the Tokmak river on the Western Pryazovian. The obtained results showed that the Paleoarchean tonalite gneisses are distributed not only in the Orekhov-Pavlograd structure but also in the West Azov block. The following age sequence of the formation of the metamorphic rocks and granitoids was established: tonalite gneisses (melanosome of migmatites) - 3.56 Ga, basic crystalline schists, band of the granodiorites and leucocratic granites (leucosome of migmatites) - 2.8 Ga, and the intersecting pegmatoid granites - 2.04 Ga. The Mezoarchean and Paleoproterozoic shear-zones of the viscoplastic deformations of the Archean rock complexes in the West Azov block were identified. They have submeridional and sublatitudinal directions respectively. These structures are widely distributed on Azov megablock. They are confined to the contact zones of the Archean microblocks. It was established that the garnet-biotite gneisses of this area could be formed by Paleoarchean tonalites. The tectonic zone which limits the above mentioned structure was formed in the Paleoproterozoic around 2.04 Ga years ago. Keywords: The Paleoarchean, geochemistry, tonalite gneiss, shear-zone, isotopic age, zircon, monazite, West Azov block, the Ukrainian Shield.