Early island-arc granitoids of the Shchuchinskaya zone of the Polar Urals: U–Pb (SIMS) zircon isotope data

Abstract

Granitoids of the Rechnoy and Yalya-Pe paleovolcanoes, which were ascribed to the Silurian Khoimpe complex during a geological mapping, and granitoids of the Nganotsky-1 and Nganotsky-2 plutons that were ascribed to the Early Devonian Yunyaga complex were studied in the Shchuchinskaya zone of the Polar Urals. It was established that according to the mineral and chemical compositions the rocks of the plutons studied correspond to island-arc granitoids of I-type. Zircons from granitoids of the Rechnoy and Yalya-Pe paleovolcanoes and the Nganotsky-1 pluton yielded concordant U–Pb (SIMS) isotope ages of 456 ± 6, 454 ± 4, and 463 ± 3 Ma, respectively, which indicates the existence of an island arc within the Shchuchinskaya zone starting from the Middle–Late Ordovician. Based on the obtained zircon ages of granitoids, the country volcanics were ascribed to the Syaday Formation; the upper stratigraphic boundary of their formation was specified as the Middle–Upper Ordovician.