PALEOARCHAEIC (3.5 BILLION YEARS) AGE OF TRONDIEMITES OF THE KURSK-BESEDINA BLOCK OF KMA

The hornblende-biotite gneisses of the Kursk-Besedyne block of the KMA Domain correspond to the rocks of the TTG series in terms of their chemical composition. The REE pattern is dominated by light REEs (La/Yb)N= 13.3); heavy REEs are not fractionated, indicating the absence of garnet in the residue of their magmatic source. They could have formed during the melting of the thickened basaltic crust. The U-Pb age of zircon from hornblende-biotite gneisses, obtained by the LA-ICP-MS method, is 3504 ± 8 Ma. Hafnium isotope composition in zircon corresponds to the chondrite reservoir. The mafic crust hafnium model age is ca. 3.95 Ga. The TTG association of the Kursk-Besedyne block is coeval to tonalites of the northern part of the Orikhiv-Pavlohrad structure of the Azov Domain of the Ukrainian Shield. TTG magmatism of this age probably completes the stage of formation of the early crust in the Azov and KMA domains.