The first U-Pb (SHRIMP-II) dating of the Reftinsky massif granitoids (eastern zone of the Middle Urals)

The article presents the results of U-Pb dating (SHRIMP-II, the Center for Isotope Research of the A.P. Karpinsky Russian Geological Research Institute) of zircon grains from leucogranite dating back to the final formation stage of the Reftinsky gabbro-granitoid massif, which is one of the largest magmatism areas of this type in the Urals. The intrusive formations of the dated magmatism episode form a sub-meridionally elongated chain of small (up to 5 km in diameter) bodies, which intrude the Silurian plagioclase granitoids building up the main part of the massif. These bodies are dominated by granodiorites, granites, and leucogranites with some gabbro, gabbronorites, diorites, and quartz diorites. By the chemical composition, the study rocks belong mainly to the moderate-potassium calc-alkaline series. The silica-rich petrographic rock varieties have a high-potassium composition. The concordant age of zircons from leucogranites is 396 ± 3 Ma. So, the formation of zircons falls in the same time interval with a significant episode of endogenous activity, i.e. the existence of the Devonian island arc within the Middle Urals (from the second half of the Emsian through the beginning of the Frasnian).