Research subject. Rocks of the Paleozoic Eastern Ural microcontinent and Magnitogorsk island arc occupy a significant part of the Southern Urals and some part of the Middle Urals. The Western Urals are composed of rocks of the ancient Baltic continent and overthrust oceanic rocks. In the Eastern Urals and Trans-Urals rocks of the accretion complexes, oceanic crust, island arcs, the Eastern Ural microcontinent and the Kazakhstan Paleozoic continent are widespread. Rocks are exposed in the Denisov tectonic zone. The Magnitogorsk simatic Island Arc originated in the Ural Ocean, near the Baltic continent, in the early Devonian, developing from the Emsian to the Famennian. A collision between the Magnitogorsk arc and the Baltic continent occurred in the Famennian century. In the pre-Carboniferous age, the Eastern Ural microcontinent was located in the Ural Ocean. In the Tournaisian period, the Eastern Ural microcontinent accreted with the Baltic continent. The Kazakhstan continental massif was located on the other side of the Ural Ocean. The volcanic belt above the subduction zone was active on the edge of the Kazakhstan continent in the Early–Middle Devonian and in the Early Carboniferous. A subduction under the Baltic and Kazakhstan continents consumed most of the crust of the Ural Ocean by the middle of the Bashkir century. As a result, the Baltic continent (together with the Eastern Ural microcontinent) came into contact with the Kazakhstan continent. The formation of folded orogen began in the Moscow century following the collision of sialic terrains.Materials and methods. The research was based on the relevant data obtained by several researchers in 2000–2018 on rock paleomagnetism. Results. The paleolatitudinal positions of the Eastern Ural microcontinent were determined, comprising 5.3 ± 7.4°) in the Middle Ordovician and 8.2 ± 7.2° in the Early–Middle Silurian. The respective paleolatitudinal positions for the Early–Middle Devonian comprised: the Ural margin of the Baltic paleocontinent (7.7 ± 3.7°), the Magnitogorsk island arc (3.2 ± 3.1°) and the Ural margin of the Kazakhstan paleocontinent (20.6 ± 3.8°).Conclusion. According to the analysed paleomagnetic data, in the Early–Middle Devonian, the distance between the latitudes of the margins of the Baltic and Kazakhstan continents was not less than 600 km provided they were in the same hemisphere, and more than 2,300 km provided they were in different hemispheres. The convergence of the terrains was associated with the subduction of the Ural Ocean crust before its closure, which occurred in the Tournaisian century.

Research subject. In this paper, we set out to investigate main paleostructures in Kazakhstan. In particular, we attempt to clarify or revise their existing geodynamic structures and to show key stages in their development on the basis of new data on the age of some stratigraphic units and rocks of the ophiolitic association.Materials and methods. The work was based on the materials of long-standing geological research performed by the authors, including government-funded geomapping, tectonic zoning and paleoreconstruction, as well as the revision of literature data.Results. It is shown that the main sedimentary, volcanogenic, volcanogenic-sedimentary and intrusive complexes were originated in the western part of the Central Asian fold belt (Paleozoic Kazakhstan) in place of various structures differing in their geodynamic environment and tectonic history throughout the Proterozoic and entire Paleozoic periods. The Epigrenville microcontinent disintegrated into individual massifs has been described, along with rift depressions, basins with oceanic crust, island arcs and island arc systems, the Epicaledonian continent, continental depressions, regional volcano-plutonic belts and marginal basins. The tectonic zonality of Kazakhstan has been presented in the form of diagrams. The mapping of the Precambrian Ulutau massif has been conducted. The distribution of the Devonian complexes and the Late Paleozoic complexes of Kazakhstan is schematically represented.Conclusions. We have refined and partially revised the existing concepts and tectonic consecution on the territory of Kazakhstan. On the basis of paleoreconstructions, key stages in the development of main paleostructures have been established; features of the geological evolution of Kazakhstan paleozoids and their relationship with tectonic processes in the Central Asian fold belt have been determined. It is shown that the modern structure of Kazakhstan paleozoids was evolving over a long period and in many stages for almost 900 million years.

The formation of an island-arc back-arc slope is considered based on the of the Upper Cambrian‒Middle Ordovician arc in the Chingiz Range in eastern Kazakhstan. The study demonstrates its occurrence during waning volcanic activity in the island-arc structure, from the end of the early Arenig (end of the Floian Age of the Early Ordovician) with the appearance of tephroturbidites. After the cessation of volcanism, two sedimentation cycles were distinguished in the slope’s sedimentary sequence in the Middle Ordovician: (1) transgressive when the island arc submerged (2) and regressive when the Chingiz arc began to build up at the beginning of the Llanvirn (Darriwilian). Sedimentation was repeatedly accompanied by landslide processes, which ended in the middle of the Llanvirn (Darriwilian) with breakup of the tectonic-gravity plate composed of Upper Cambrian volcanic rocks with limestone in the sole, caused coarsely fragmented mixtite to form in front of the allochthonous mass and the further sedimentation on the back-arc slope to stop.

Рассмотрены и обобщены геологические материалы, полученные к настоящему времени по территории Казахстана и Тянь-Шаня. На этой основе показаны главные особенности строения выделяемых там разнотипных и разновозрастных палеоструктур – континентальных массивов, бассейнов с океанической корой, островных дуг, краевых вулкано-плутонических поясов, а также зон трансформных разломов. Выяснены характер и возможные причины их эволюции и преобразований, отразившихся на формировании и развитии мозаичного структурного ансамбля на окраине существовавшего с неопротерозоя Палеоазиатского океана. Выделены и проанализированы основные этапы геодинамических изменений в истории палеозоид Казахстана и Тянь-Шаня и предложена модель вероятного хода тектонических событий в регионе. Модель проиллюстрирована с использованием опубликованных палеомагнитных данных, серией палеотектонических реконструкций, построенных для интервалов времени 950–900, 850–800, 750–700, 650–630, 570–550, 530–515, 500–470, 460–440 и 390–380 млн лет.

Structural relationships between the Neoproterozoic rock complexes of a continental massif, island arc and back-arc basin geodynamic affinities are described and considered in this work based on field observations within the northeastern segment of the Central Taimyr tectonic zone distinguished in the late Hercynian fold-thrust belt of the Taimyr Peninsula. As is established for the first time, rock complexes of the continental massif with the early Late Riphean (Tonian-Cryogenian) volcanogenic-sedimentary cover occur in the study region as the allochthonous syn- and post-sedimentary thrust sheets buried in, or thrust over deposits of a back-arc basin, which accumulated in the terminal Late Riphean (Cryogenian)-initial Vendian (Ediacaran). These and other results of the large-scale structural observations elucidate important details of the tectonic development in the Late Precambrian, when two lateral ensembles of the Neoproterozoic structures originated in the region. In the first half of the Neoproterozoic, the regional tectonic ensemble included the oceanic plate abutting on the continental massif with a volcano-plutonic belt. The subsequent system of an island arc and marginal back-arc basin originated in the second half of the Neoproterozoic and existed approximately till the mid-Vendian (Ediacaran) phase of the intense formation of thrust sheets and folds (Baikalian orogeny).

Geological information on Kazakhstan and the Tien Shan obtained up to the present time has been considered and integrated in order to demonstrate the main features of continental massifs, basins with oceanic crust, island arcs, marginal volcanic-plutonic belts, and transform fault zones differing in type and age. We ascertained the character and probable causes of their evolution and transformations resulting in the origination and development of mosaic structural assembly at margin of the Paleoasian ocean that existed from Neoproterozoic. The main stages of the geodynamic history of Paleozoides in Kazakhstan and Tien Shan are characterized, and a model of the probable course of regional tectonic events has been proposed. This model is illustrated by published paleomagnetic data and a series of paleotectonic reconstructions for time intervals 950–900, 850–800, 750–700, 650–630, 570–550, 530–515, 500–470, 460–440, and 390–380 Ma.

The main stages of the evolution of newly formed structural elements are considered against the background of breakup of the epi-Grenville Rodinia supercontinent, which started about 950 Ma ago. The paleomagnetic data on pathways of the traveling of Rodinia’s fragments are analyzed and evidence for their geology, magmatism, and sedimentation are integrated with special emphasis on the evolution of the continental margins. A series of paleotectonic maps with elements of paleogeography for time intervals of 950–900, 850–800, 750–700, 650–630, and 570–550 Ma ago has been compiled on the basis of palinspastic reconstructions with allowance for new paleomagnetic data primarily concerning the position of Siberia in the Late Precambrian. Objects all over the world, not only in Russia, are involved in the analysis, though with less thoroughly described paleogeography. The structural elements of the Paleoasian ocean are included into the system of global paleooceans and framing paleocontinents. The history of the Paleoasian ocean is traced through 400 Ma from the breakup of the Rodinia supercontinent to the origin of the new Paleogondwana supercontinent about 550 Ma ago.

The main differences and similarities between the tectonic features of the Urals and the Tien Shan are considered. In the Neoproterozoic and Early and Middle Paleozoic, the Ural and Turkestan oceanic basins were parts of one oceanic domain, with several distinct regions in which tectonic events took different courses. The Baltic continental margin of the Ural paleoocean was active, whereas the Tarim-Alay margin of the Turkestan ocean, similar in position, was passive. The opposite continental margin in the Urals is known beginning from the Devonian as the Kazakh-Kyrgyz paleocontinent. In the Tien Shan, a similar margin developed until the Late Ordovician as the Syr Darya block with the ancient continental crust. In the Silurian, this block became a part of the Kazakh-Kyrgyz paleocontinent. The internal structures of the Ural and Turkestan paleooceans were different. The East Ural microcontinent occurred in the Ural paleoocean during the Early and Middle Paleozoic. No microcontinents are established in the Turkestan oceanic basin. Volcanic arcs in the Ural paleoocean were formed in the Vendian (Ediacarian), at the Ordovician-Silurian boundary, and in the Devonian largely along the Baltic margin at different distances from its edge. In the Turkestan paleoocean, a volcanic arc probably existed in the Ordovician at its Syr Darya margin, i.e., on the other side of the ocean in comparison with the Urals. The subduction of the Turkestan oceanic crust developed with interruptions always in the same direction. The evolution of subduction in the Urals was more complicated. The island arc-continent collision occurred here in the Late Devonian-Early Carboniferous; the continent-continent collision took place in the Moscovian simultaneously with the same process in the Tien Shan. The deepwater flysch basins induced by collision appeared at the Baltic margin in the Famennian and Visean, whereas in the Bashkirian and Moscovian they appeared at the Alay-Tarim margin. In the Devonian and Early Carboniferous, the Ural and Turkestan paleooceans had a common active margin along the Kazakh-Kyrgyz paleocontinent. The sudduction of the oceanic crust beneath this paleocontinent in both the Urals and the Tien Shan started, recommenced after interruptions, and finally ceased synchronously. In the South Ural segment, the Early Carboniferous subduction developed beneath both Baltica and the Kazakh-Kyrgyz paleocontinent, whereas in the Tien Shan, it occurred only beneath the latter paleocontinent. A divergent nappe-fold orogen was formed in the Urals as a result of collision of the Kazakh-Kyrgyz paleocontinent with the Baltic and Alay-Tarim paleocontinents, whereas a unilateral nappe-fold orogen arose in the Tien Shan. The growth of the high divergent orogen brought about the appearance of the Ural Foredeep filled with molasse beginning from the Kungurian. In the Tien Shan, a similar foredeep was not developed; a granitic axis similar to the main granitic axis in the Urals was not formed in the Tien Shan either.

Lower Ordovician sequences of the Ebeta antiform, a southern extension of the Uraltau zone, were deposited at the conjugation of paleocontinental and paleoceanic sectors of the southern Urals. Four types of sections were formed on opposite sides of cordillera that existed at the margin of the East European paleocontinent on the Preordovician volcanic belt. Sections of the first three types made up the western apron on the uplift that served as a provenance. Lateral and vertical relationships of various sedimentary associations, as well as their variable (in space and time) facies patterns and sedimentation conditions are considered. An important role of redeposition, slumping, and faulting in the apron development has been revealed. The apron fringed the eastern wall of the Sakmara marginal riftogenic basin that arose at the Cambrian-Ordovician boundary. On another side of the marginal uplift in the east, a slightly modified perioceanic environment existed in the Early Ordovician. Sections of another type formed here at the periphery of Uralian paleocean. These sections are characterized by the universal occurrence of ophiolithoclastic olistostrome with fragments of an older oceanic crust.

A new model of tectonic evolution of the southern Urals is suggested based on data pertaining to the junction of paleocontinental and paleoceanic segments where various rock associations differing in their ages, compositions, and structure are tectonically juxtaposed. It is suggested that an oceanic basin existed along the Ural margin of the East European paleocontinent during at least 250-270 Ma from the Vendian to the Late Devonian. A marginal volcanic belt was located at the boundary between the East European paleocontinent and the proto-Ural ocean in Vendian-Early Cambrian time, and an accretionary wedge was formed at its eastern periphery. At the Cambrian-Ordovician boundary, the Uraltau uplift (borderland) originated on their spot and separated the oceanic region from the Sakmara riftogenic trough, which had been formed to the west of it. The second, Middle Ordovician to Middle Devonian, (paleo-Ural) pulse in the evolution of the active continental margin was related to the buildup of the Guberlya island arc on the borderland's margin. The Sakmara backarc basin was formed behind the arc and reached its maximum width in the Late Silurian-Early Devonian. Within the oceanic domain, the Magnitogorsk island-arc system facing the East European paleocontinent evolved at that time. The geodynamic environment changed in the Middle Devonian as a result of an eastward thrusting of the East European paleocontinent under the Magnitogorsk island arc. The tectonic stacking gave rise to the formation of intrabasinal cordilleras and, as a consequence, to the accumulation of thick mixtite-olistostrome units. The tectonic juxtaposition of various geological complexes initially occurred within the Sakmara basin, and then encompassed the Guberlya island arc and the western part of the paleo-Ural oceanic region. The tectonic stacking culminated in the Late Devonian and Carboniferous and brought about the formation of an asymmetric fanlike multilayer nappe-and-fold edifice with its axial ophiolitic suture extending along the Main Ural Fault. The divergent orogenic structure was reworked during the final stage of the East European paleocontinent underthrusting in the Late Paleozoic with the westward squeezing of the paleo-Ural complexes upon the margin of the paleocontinent and their variable strike-slip displacements.

Carbon and oxygen isotope variation curves for Vendian-Lower Cambrian carbonates of the Bokson Group are correlative with those characterizing coeval sections in Siberia and western Mongolia. The curves demonstrate the following characteristics of sediments: (1) abnormally high values of delta(13)C (up to 6 parts per thousand PDB) and delta(18)O (up to 31 parts per thousand SMOW) at the base of the section, which are also typical of basal beds of the Tsganolom Formation of western Mongolia; and (2) a sharp decrease of both values (down to -5 parts per thousand and 25-26 parts per thousand, respectively) in the lower part of the Tabinzurta Formation like in Siberian and West Mongolian sections close to the base of the Manykaian (Nemakit-Daldynian) Stage. On the basis of isotopic correlation, the Zabit Formation can be attributed to the Vendian. The lower boundary of the Manykaian (Nemakit-Daldynian) Stage is distinguished at the level of 75-100 m above the base of the Tabinzurta Formation, whereas the lower Tommotian boundary is placed at the level of 400-450 m from the base of this formation, and the Tommotian-Atdabanian boundary is assumed to be at the level dividing the Tabinzurta and Khuzhirtai formations. Basal diamictites of the Zabit Formation seem to be correlative with the Laplandian glacial horizon of the Early Vendian. Origin of isotopic anomalies and their possible relations to climatic events are discussed.