Geochemistry, zircon U-Pb age and Hf isotopes of the North Muya block granitoids (Central Asian Orogenic Belt): constraints on petrogenesis and geodynamic significance of felsic magmatism

The Baikal-Muya Foldbelt is one of the oldest and the most enigmatic terrain among the Central Asian Orogenic Belt. During the Early (1.0-0.8 Ga) and Late (0.8-0.6 Ga) Neoproterozoic orogenic cycles a notable amount of juvenile crust has been formed in subduction-collision settings along with the reworking of the existing Early Precambrian continental crust. The latter is perfectly presented within the North Muya metamorphic block (Anamakit-Muya zone) including the oldest high-pressure subduction-related rocks in the Central Asia. In order to evaluate the process of the juvenile crust formation in the Precambrian continental unit, whole-rock trace elements along with zircon U-Pb ages and Hf-isotopic composition were analyzed in granites of unknown age that intrude the Precambrian volcanic-sedimentary rocks of the Parama series in the southern North Muya Block. Combined geochemical and zircons isotopic studies indicate the formation of granites with the main pulse at ~810 Ma due to partial melting of a juvenile mafic crust accompanied by reworking of the older crustal material from the continental arc basement. The composition of the granites was controlled by processes of intracrustal differentiation together with a probable contamination by older crustal substrate. Geochemistry and age of the studied granites are comparable to the granites of the Muya complex observed in the volcano-plutonic Kelyana-Irokinda zone. It is assumed that the Muya block and the Kelyana-Irokinda zone (terrane) had possibly been parts of the large continental-arc system beyond the Siberia margins.