Neoproterozic anorogenic rhyolite-granite volcanoplutonic association of the Aktau-Mointy sialic massif (Central Kazakhstan): Age, source, and paleotectonic position.

Rhyolite-granite volcanoplutonic association was identified among the Precambrian basement complexes of the Aktau-Mointy Massif, Central Kazakhstan. This association comprises rhyodacites, rhyolites, subalkaline rhyolites, tuffs, and felsic volcanogenic-sedimentary rocks of the Altyn Syngan and Urkendeu formations, as well as granitoids of the Uzunzhal Complex. U-Pb (ID-TIMS) dating of accessory zircons from the volcanic rocks and granites showed that the association was formed in the Neoproterozoic (Tonian, 925-917 Ma). The Neoproterozoic volcanic rocks and granites are the youngest Precambrian magmatic complexes and mark the final stage in the formation of the Precambrian crust of the Aktau-Mointy Massif. In terms of major and trace element composition, the volcanic rocks and granites resemble A-type granites, thus indicating the within-plate settings of their formation. It was established that their primary magma could be derived by melting of metatonalitic or metagraywacke protolith at T ≥ 940°C and P ∼ 8-10 kbar in response to mantle magma underplating. Sm-Nd isotope data on the volcanic rocks and granites (T(DM) = 1.9−1.7 Ma, ɛ(T) from −1.9 to −3.5) testify the Paleoproterozoic age of their crustal protolith. Available data have revealed strong similarity between the Neoproterozoic tectonomagmatic evolution of the Aktau-Mointy Massif and the Congo-São Francisco paleocontinent, which, with other cratons, composed the southern Rodinia supercontinent. This suggests that the formation of the Tonian anorogenic volcanoplutonic association of the Aktau-Mointy sialic massif was related to the global-scale divergent processes in the southern Rodinia supercontinent (Congo-São Francisco paleocontinent). [ABSTRACT FROM AUTHOR]