Early stages of the Paleo-Asian ocean evolution at the western margin of the Siberian Craton: petrological, geochemical and geochronological evidence

The paper explores the geological, geochemical, and isotope-geochronological evidence of the events at the final stage of the Neoproterozoic history of the Yenisei Range (starting from the formation of oceanic crust fragments in the region and their accretion to the Siberian Craton until the post-accretionary stage of crustal tension and onset of the Caledonian orogeny). Having analyzed new data on the petro-geochemical composition, age, and geodynamic nature of the formation of contrasting rocks composing the tectonic mélange of the Near Yenisei (Prieniseiskaya) regional shear zone, we discovered a chronological sequence of events that marks the early stages of the Paleo-Asian Ocean evolution at its junction with the Siberian Craton. These events are documented by the continental marginal, ophiolitic, and island-arc geological complexes, each of which has different geochemical features. The most ancient structures are represented by fragments of the oceanic crust and island arcs from the Isakovka terrane (700–620 Ma). The age of the glaucophane-schist metamorphic units that formed in the paleosubduction zone corresponds to the time interval of 640–620 Ma. The formation of high-pressure tectonites in the suture zone, about 600 Ma BP, marks the final stage of the Isakovka block accretion to the western margin of the Siberian Craton. The final events in the early history of the Asian Paleo-ocean were related to the formation of Late Vendian riftogenic amygdaloidal basalts (572 ± 6.5 Ma) and intrusion of post-collisional leucogranites of the Osinovka massif (550–540 Ma), which cut through the earlier oceanic crust fragments in the Isakovka terrane. These data allow us to refine the Late Precambrian stratigraphic scheme in the northwestern Trans-Angarian part of the Yenisei Range and the evolutionary features of the Sayan–Yenisei accretionary belt. The revealed Late Neoproterozoic landmarks of the evolution of the Isakovka terrane are attributed to the terminal phase of the breakup of Rodinia, separation of the Siberian Craton, and opening of the Paleo Asian Ocean.