TERRANES IN EAST MONGOLIA AND CENTRAL TRA NSBAIKALIA AND EVOLUTION OFTHE OKHOTSK-MONGOLIAN FOLD BELT

Within investigations on the Global Geoscience Transects International Project, an East-Mongolian transect has been compiled on the basis of the complex interpretation of geological and geophysical data. A seri es of terranes making up Central Transbaikalia and East Mongolia has b een distinguished, and the geodynamic nature and time-spatial relation ships between these tectonic units have been elucidated. The terranes are made up of Vendian-Early Paleozoic, Middle-Late Paleozoic, and Lat e Paleozoic-Early Mesozoic island arcs and microcontinents. In additio n, the Middle-Late Paleozoic and Late Paleozoic-Early Mesozoic active continental margins of the Andean type, the Late Paleozoic-Early Mesoz oic passive margins, and the Early Cretaceous continental rifting are considered. The formations of island arcs and active continental margi ns of the Andean type are thrust over the adjacent continents and micr ocontinents, with the tectonic sheets extending for up to 150 km acros s their strike. Schematic paleodynamic reconstructions have been carri ed out for the Devonian-Late Jurassic Okhotsk Mongolian ocean and its environs. The origin of the collision of the Siberian and Mongolian-Ch inese continents in the transect region is assigned to the end of the Early Jurassic - the beginning of the Middle Jurassic. However, the de formations and magmatism caused by this collision and completed the Ok hotsk-Mongolian fold belt formation continued approximately up to the end of the Late Jurassic. Large areas of magmatism manifestation and t he presence of a mantle component in this magmatism are the result of the overlapping of the oceanic rift (a hot zone in the mantle) by a th ick continental lithosphere during the Okhotsk-Mongolian ocean closure . In the Late Cretaceous the collision setting changed into the contin ental rifting.