Two episodes of subduction-related intrusive magmatism within the Pechora zone of the Pechora basin basement

The Pechora Basin is the largest tectonic structure of the Pechora Plate. It is located between the Timan and the Cis-Ural Foredeep. The Upper Precambrian sedimentary-metamorphic and igneous rocks of the basement are completely overlain by a sedimentary cover, therefore, the geological structure of the basement is known only on the basis of geophysical data and core samples from boreholes up to 5 km deep. The basement has a heterogeneous structure. It includes complexes of the Late Precambrian passive margin of the East European continent, which compose the Timan megablock (Izhma zone with Timan adjoining from the southwest) and formations formed in an active margin geodynamic setting combined into the Bolshezemel megablock (Pechora and Bolshezemel zones). The boundary between megablocks is the Pripechora fault (suture) zone. The age of igneous rocks of the basement is debatable; therefore, U-Pb (SIMS) studies of single zircon grains are undertaken to specify it. The article presents petrogeochemical data and U-Pb (SIMS, SHRIMP-RG) ages of zircon grains from plutonic rocks of the Pechora zone belonging to the Bolshezemel megablock drilled by two boreholes at depths of ~ 4.5 km. The obtained results indicated two episodes of island-arc magmatism. The first took place at the end of the Riphean, and the second was confined to the Early-Late Vendian boundary. The age of gabbrodiorites from the 1-Severny Savinobor borehole, interpreted as early island-arc rocks, is 673 ± 7 Ma. Late island-arc plagiogranites from the 1-Novaya borehole yield the age of 564 ± 5 Ma and precede the orogenic granitoids of the Pripechora fault zone which are dated (U-Pb) to 555-544 Ma.