Research subject. This article is devoted to the formation features of the Ural-Timan-Paleo-Asian segment of Eurasia. Materials and methods. The research was based on the authors’ data and those obtained following a review of available publications on the geology of segmentation. The Timan region was investigated using the geological information obtained by V.G. Olovyanishnikov.Results. A geodynamic map of the Ural-Timan-Paleo-Asian segment with a scale of 1 : 2 500 000 was compiled, which allowed further research into the structure and formation of the north-western part of the Eurasian area. This part was found to be mostly composed of geodynamic associations of orogens, orogenic systems and orogenic belts of the Upper Proterozoic (Riphean) and Paleozoic time intervals, as well as by elements of the Mesozoic-Cenozoic neoplate. These processes were supplemented by the formation of tectonic systems of superimposed depressions and protoplate protrusions. The formation of orogens, orogenic systems and orogenic belts is associated with the development and subsequent transformation of paleooceanic basins under the conditions of accretion and collision. The terranes of the ancient continental crust also participated in the formation of the segment’s geodynamic elements, for which a typification scheme was proposed. The articles present new data on the formation conditions of the segment’s orogenic elements and the relationship of the orogeny with global reconstructions, including the problem of closing the surrounding oceanic space.

This paper reports on the first U–Pb dating of zircons from dacites of the volcanic paleo-edifice of the andesite–dacite complex of the Eastern Zone of the Middle Urals orogen. The Eastern Zone involves the retroshariage and sheet-folded structural subzones. The volcanic complex, which includes vent and peri-vent facies, lies in the sheet-folded subzone among flyshoid and carbonate deposits with Middle Devonian fauna. This subzone forms the easternmost border of the orogen. The age of zircon grains is 389 ± 5.6 Ma, which is also in accordance with the Middle Devonian. Therefore, the sedimentary and volcanic complexes were formed around the same time, but based on their composition and structure, in different facial conditions. The sedimentary deposits were accumulated in shallow basins; the volcanic deposits were likely formed in the subaerial conditions surrounded by a shallow sea basin. We suppose that the manifestation of andesite–dacite volcanism in association with the sediments of shallow basins most likely points to the spatial and age-related displacement of the geodynamic and facial conditions of volcanism to the eastern periphery of the orogen.

Приводятся результаты впервые выполненного U-Pb-датирования цирконов из дацитов вулканической палеопостройки андезит-дацитового комплекса Восточной зоны среднеуральской части Уральского орогена, состоящей из ретрошарьяжной и покровно-складчатой структурных подзон. Вулканогенный комплекс, включающий жерловые и прижерловые фации, залегает среди флишоидных и карбонатных отложений с фауной среднего девона в покровно-складчатой структурной подзоне, образующей крайнее восточное ограничение орогена. Возраст зёрен циркона составил 389 ± 5,6 млн лет, что также отвечает среднему девону. Следовательно, формирование осадочного и вулканогенного комплексов происходило в близком возрастном интервале, но, судя по их составу и строению, в разных фациальных условиях. Осадочные образования накапливались в мелководных бассейнах, а вулканические формировались, по-видимому, в субаэральных условиях в окружении мелководного морского бассейна. Предполагается, что проявление андезит-дацитового вулканизма в ассоциации с осадками мелководных бассейнов, скорее всего, свидетельствует о пространственном и возрастном смещении к восточной периферии орогена геодинамических и фациальных условий вулканизма.

Subject of study. Different points of view on the concept of structures of the terrain type and their role in the addition of orogenic belts are considered. Materials and methods. We used our own research and analysis of the latest publications about the Ural-Timan region and the Pacific belt, on the territory of the Northeast segment of Eurasia, as well as currently known isotope radiometric data. It was used also the result of geophysical seismotectonic and paleomagnetic explorations. Results. It has been established that in the composition of the Ural-Timan structural area, along with the Proterozoic and Paleozoic associations of the orogenic belts and the Riphean sedimentary series of protrusions of the Russian Plate, structural formations that correspond to the terrain of the continental crust take part. They are the most characteristic for the Ural orogenic belt, which belongs to the group of epiokean-type belts, associated with the transformation of ocean basins with the active participation of accretion and collision processes. The parametric features of these terrains include the ancient age characteristics of terrain rocks, their position in the belt structure, as well as the presence of relics of subhorizontal layered structural elements. The discordant blocks of migmatites, gneisses and other metamorphic rocks of Precambrian age, which make up the terrains, was the basis for the introduction of the term “terranes of the ancient continental crust”. By connection with the source, exotic and endemic, and simple and complex terrains are distinguished by structure. The geodynamics of including terrains of the ancient continental crust into the structure of orogenic belts is associated with horizontal movements of fragments of the ancient lithosphere in oceanic paleobasins to the periphery of the Russian Plate and their localization in belt structures. The formation of these terrains in the structures of the orogenic belts is completed by the formation of the intra-terrain massifs of granitoids and belts of volcanic-intrusive series. Supporters of a different methodology, dominant among researchers of the Pacific Belt of the Northeast Segment of Eurasia, refer to terrains all the structural elements that perform orogenic belts, because they believe that they have undergone horizontal movements and are in allochtonous occurrence. Conclusions. It has been established that in different geological provinces the term terrain has its own characteristics. This was the basis for the selection of two geodynamic types of terrains.

Within Sukhoy Ljg-Techa zone of accretion-collision segment of the eastern periphery of the Urals dolerite and gabbro-dolerite dykes and sills are widespread among Upper Devonian-Low Carboniferous terrigenous and carbonate deposits. Geochemical data indicate that dolerites peculiar features of intraplate formations. Features of their structural position and dolerite petrogeochemical characteristics suggest that they formed at the stretch of composite continental crust with important role of large continental terraines.

Methodology of geological zoning of orogenic belts, adequate to mobilistic paradigma, should be in a natural way correspond to geodynamics conception, taking into consideration the positions of lithospheric plate tectonics. For this purpose the methodology of tectonic-geodynamical zoning is being suggested. The base of such zoning is the distinguishing of zones with associations of one-type geodynamical regimes and environments and their structural combinations during the formation on the crust of oceanic type and localization in interplate position or on the boundaries of tectonic plates as a result of horizontal dislocations with the accretion and collision process manifestation. In its turn at the continental type crust in stable regimes folded systems have been formed. On this basis the particularities of tectonic-geodynamic zoning of the Ural-Timan-Paleoasian segment of Eurasia have been considered, general scheme of its zoning has been given as an example of the suggested methodology usage. A segment can be considered as a genotype of orogenic belts, being formed at the expense of the plate-tectonic accretion of oceanic basin on the craton periphery.

The first-order geodynamic domains of the Uralide orogen constitute a relatively simple pattern across the orogenic belt. Continental rifting along the western margin is expressed by a system of Vendian-early Palaeozoic structures with shale-hosted siderite and magnesite and basalt-hosted base metals. It is superimposed on a Middle Riphean rift system with layered mafic-ultramafic complexes with chromite and ilmenite-titano-magnetite and subordinate ophiolite massifs with gold and magnetite. An oceanic spreading domain, immediately east of the Main Uralian Fault is associated with chromite, titano-magnetite and massive sulphide deposits (Dombarovsky or Cyprus type). Further east, bimodal volcanic associations in island arcs with oceanic crust have formed copper-zinc massive volcanic sulphide deposits (Uralian type). Subsequently, complex volcanic sulphide deposits are associated with belts of andesite-dacite and co-magmatic diorite (Baymak or Kuroko type). The eastern, destructive, margin of the orogen is characterized by magnetite and copper-magnetite skarns and porphyry systems. Relatively small plagiogranite to granodiorite complexes, related to oceanic crust, carry scheelite and gold. Calc-alkaline granitic massifs have formed associations of tungsten, tantalum and beryllium. This pattern was dissected by major thrusts and transcurrent shear zones. Increased fluid activity in the course of deformation, inferred to have been involved in complex multi-phase gold mineralization was most probably controlled by deep-reaching faults and shears. Although the recognition of the first-order domains represents a guideline for exploration, detailed structural geological studies of the kinematics of the major faults and shear zones are required in conjunction with radiometric dating of suitable fault-and ore-associated minerals, in association with on-going deep-reaching geophysical investigations.