EVOLUTION OF STRUCTURES OF THE URALS, KAZAKHSTAN, TIEN SHAN, AND ALTAI-SAYAN REGION WITHIN THE URAL-MONGOLIAN FOLD BELT (PALEO-АSIAN OCEAN)

Abstract

On the basis of generalizations and analysis of new materials on regional and thematic research, the main problems involved with the evolution of the Paleo-Аsian ocean and structure of the huge Ural-Mongolian Fold Belt have been considered. Separate segments of the Ural-Mongolian Fold Belt resulting from the evolution of the Paleo-Аsian ocean developed in a specific fashion. Hence, Altaides, Kazakhstanides, Tien-Shanides, Uralides, Salairides, and Baikalides may be recognized within its limits. At the same time, the main stages of development of separate structures are well correlated with each other, and the paleomagnetic data and palinspastic reconstructions confirm the common evolution of the Paleo-Аsian ocean in the period 950-250 Ma. The large stages of reconstruction and closure of the Paleo-Аsian ocean are connected with superplumes, which appeared in the Permo-Triassic (Siberian), in the Devonian (European), and, possibly, in the Early-Middle Ordovician. These plumes also favored the synchronization of events in separate parts of the Paleo-Asian ocean. The best synchronization is observed in the periods of superplume appearance at about 485, 360, and 245 Ma ago, and about 120 Ma ago in the Mesozoic, at intervals of 120 Ma. The presence of these superplumes is hypothesized in the Late Precambrian as well, in a lapse of 120 Ma, thus reaching the best synchronization at around 610, 730, and 850 Ma. In the periods between these major plumes, smaller local plumes appear at an interval of about 30 Ma and, correspondingly, local synchronization of tectonic processes occurs (restructuring of island arcs and related local collisional processes, exhumation of eclogites and glaucophane schists), reflected in the maxima of isotope ages.