EARLY NEOPROTEROZOIC GRANITOIDS IN THE RYAZANOVSKY MASSIF OF THE YENISEI RIDGE AS INDICATORS OF THE GRENVILLE OROGENY AT THE WESTERN MARGIN OF THE SIBERIAN CRATON

Abstract

Studies of the geological history of the Yenisei Ridge are important not only for understanding the tectonic evolution of mobile belts at the boundaries of ancient cratons but also for problem solving whether the Siberian craton was a part of the Rodinia supercontinent. The mineralogical-petrological, geochemical and isotope-geochronological studies yielded new data on the petrogeochemical composition, petrogenesis features, U-Pb age of zircon, and Sr and 147Sm-143Nd isotopic parameters for the rocks of the Ryazanovsky granitoid massif located near the Yenisei fault zone of the Yenisei Ridge. These rocks are represented by high-ferruginous peraluminous varieties and are comparable to A-granites or highly differentiated I-granites. Their composition evolves from normal to subalkaline granites and leucogranites, characterized by increased concentrations of highly charged and radioactive elements. Isotopic (Sr, Nd) characteristics of the rocks indicate generation from an ancient crustal substrate, the average age of which corresponds to the Paleoproterozoic. The formation of these granites at the Meso-Neoproterozoic boundary (1013±9.9 Ma) corresponds to the early stage of the Grenville orogeny and the formation time of the structure of the Rodinia supercontinent. This episode of regional crustal evolution is correlated with the synchronous successions and similar style of tectonothermal events on the periphery of large Precambrian cratons (Laurentia and Baltica), thus confirming the reliability of the proposed paleocontinental reconstructions of incorporation of the Siberian craton into the Rodinia.