NEOPROTEROZOIC COLLISIONAL S-type GRANITOIDS OF THE YENISEI RIDGE: PETROGEOCHEMICAL COMPOSITION AND U-Pb, Ar-Ar, AND Sm-Nd ISOTOPE DATA
Collisional granitoid magmatism caused by the Early Neoproterozoic orogeny in the west of the Siberian craton is considered. New data on the petrogeochemical composition, U-Pb (SHRIMP II), Ar-Ar, and Sm-Nd isotopic ages of the Middle Tyrada granitoid massif in the northwestern Yenisei Ridge are presented. Plagiogranites, granodiorites, and quartz diorites of the massif are of calcareous and calc-alkalic composition. The elevated alumina contents and presence of accessory garnet permit them to be assigned to S-type granitoids. Their spidergrams show Rb, Ba, and Th enrichment, minimum Nb, P, and Ti contents, and no Sr depletion. The granitoids formed through the melting of plagioclase-enriched graywacke source, obviously Paleoproterozoic metaterrigenous rocks of the Garevka Formation and Teya Group (TNd(DM) = 2.0-2.5 Ga), judging from the isotope composition of the granitoids (TNd(DM-2st) = 2200 Ma and εNd(T) = -6.0) and the presence of ancient zircon cores (1.80-1.85 Ga). Formation of granitoids took place in the final epoch of the Grenville collision events in the late Early Neoproterozoic (U-Pb zircon age is 857.0 ± 9.5 Ma). In the Late Neoproterozoic, the granitoids underwent tectonothermal reworking caused by Vendian accretion and collision events on the southwestern margin of the Siberian craton, which explain the younger K-Ar biotite age, 615.5 ± 6.3 Ma.