V.K. KUZMIN, M.V. NAUMOV, N.V. RODIONOV, V.N. ZELEPUGIN, YU.YU. YURCHENKO (VSEGEI)

Paleoproterozoic granitoids in the Luktur Complex, the Yurovsky Uplift (Okhotsk Massif North-East of Russia): composition, age and genesis according to geochemical, Nd-Sr isotope-geochemical and U-Pb geochronological data

The Luktur granitoid complex of the Yurovka terrane is mainly composed of sub-alkali leucogranite, granite, and granosyenite with a subordinate occurrence of normal and alkali feldspar granite, as well as quartz syenite and monzonite. Granitoids are characterized by elevated alkalinity, potassium type of alkalinity, enrichment in REE, but in general, their geochemical features vary in a wide range; no differentiation trends are marked. The similarity of geochemical, Nd-Sr isotopic and U-Pb geochronological parameters of granitoids of the Luktur Complex and metavolcanics of the Yurovka Complex was identified. The Luktur granitoids resulted from the anathectic melting of variable Yurovka metamorphic lithologies. According to the parameters of Sm-Nd and Rb-Sr isotopic systems, the lower age limit of the formation of the crystalline basement of the Yurovka terrane is estimated to be 2300 Ma. The U-Pb (SHRIMP II) age based on zircon from the Luktur Complex was determined to be 1975 ± 36, 1969 ± 13 and 1964 ± 13 Ma. The combination of isotope, geochemical and geochronological data suggest that both Luktur granitoids and Yurovka metavolcanics were formed in the Paleoproterozoic. Thus, two terranes of different ages can be distinguished within the Okhotsk massif – Paleoarchean Kukhtui terrane and Paleoproterozoic Yurovka terrane.
Keywords: Okhotsk Massif, Yurovka terrane, granitoids, Palaeoproterozoic, U-Pb dating, Nd-Sr isotope systems.