The Chiron Basin extends along the southern periphery of the Siberian Craton and the western margin of the Mongol–Okhotsk Belt. Here, we present whole-rock geochemical data (major and trace elements and Sm–Nd isotopes) along with zircon U–Pb geochronology and Lu–Hf isotopic data from Paleozoic sedimentary rocks within the Chiron Basin to investigate their provenance and tectonic history. εNd(t) values of the siliciclastics rocks of the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations vary from −17.8 to −6.6, with corresponding two-stage Nd model ages (tNd(C)) ranging from 2.56 to 1.65 Ga. Detrital zircon grains from these rocks are predominantly Archean, Paleoproterozoic, and Carboniferous–Devonian in age. The data suggest that the southern flank of the Siberian Craton is the only viable source area for Archean and Paleoproterozoic zircon grains with Hf model ages (tHf(C)) of >2.20 Ga. The majority of zircon grains from sandstones from the Khara–Shibir, Shazagaitui, and Zhipkhoshi formations are Devonian–Carboniferous in age. With respect to their Hf model ages, the zircon grains can be subdivided into two groups. The first group of Devonian–Carboniferous zircon grains is characterized by relatively old (mainly Paleoproterozoic) tHf(C) model ages of 2.25–1.70 Ga and the source was the southern margin of the Siberian Craton. The second group of Devonian–Carboniferous zircon grains is characterized by significantly younger (mainly Neoproterozoic) tHf(C) model ages of 1.35–0.36 Ga, which are consistent with a juvenile source, most likely eroded island arcs. Our data, show that sedimentary rocks of the Chiron Basin likely formed in a back-arc basin on the southern periphery of the Siberian Craton facing the Paleozoic Mongol–Okhotsk Ocean.

The article presents the results of comprehensive geological and geochemical study of the sedimentary rocks of the Upper Paleozoic Shazagaitui and Zhipkhoshi formations filling the upper part of the Chiron Basin, as well as U–Pb geochronological and Lu–Hf isotopic studies of zircons from these formations. The geochemical features of the terrigenous rocks of the Shazagaitui and Zhipkhoshi formations indicate that they were formed in a subduction zone environment. The presence of conglomerates and gravelstones and the predominance of unrounded and subrounded fragments in the rocks of the Shazagaitui and Zhipkhoshi formations also indicate their sedimentation in tectonically active zones. The abundant detrital zircons of Paleoproterozoic age, as well as the Paleoproterozoic and Archean Hf model ages of most of the zircons in the sandstones of the Shazagaitui and Zhipkhoshi formations, suggest that the main source of sediment clasts for these formations are the magmatic and metamorphic rocks of the southern surrounding of the North Asian Craton. However, the presence of Devonian–Carboniferous zircons with relatively young (mostly Neoproterozoic) Hf model ages is evidence that these zircons in the sedimentation basin were derived through erosion of mature (?) island arcs, but the contribution of this source is minor. The obtained results in combination with our regional geological data from previous studies suggest that the sediments of the Shazagaitui and Zhipkhoshi formations were accumulated in a basin setting on the southern framing of the North Asian Craton facing the Paleozoic Ocean.

We report the results of geochemical, Sm–Nd isotope–geochemical, and U–Pb detrital zircon geochronological studies of metaterrigenous rocks of the Glubokin Formation assigned provisionally to the Upper Riphean. This formation is developed where the Mongol–Okhotsk belt is almost completely squeezed by the surrounding continental structures and, hence, bears important information on its evolution. The obtained results suggest the following conclusions: (1) the Glubokin Formation is Early Pennsylvanian or post-Early Pennsylvanian in age, not Riphean as previously suggested; (2) the Glubokin Formation belongs to the Mongol–Okhotsk Fold Belt rather than to the Argun continental massif, as suggested in the existing schemes of structural zoning; (3) the volcanogenic-terrigenous deposits of the Glubokin Formation were precipitated in a back-arc basin setting above the subduction zone subsiding beneath the southeastern margin of the North Asian Craton; and (4) the main sources of clastic material for the Glubokin Formation were igneous and metamorphic complexes of different ages from the southeastern margin of the North Asian Craton.

This paper reports the results of complex geochemical and Sm–Nd isotope-geochemical studies of terrigenous rocks of the Upper Amur and Zeya–Dep troughs, as well as U–Pb geochronological studies of detrital zircons. It is established that the studied troughs have orogenic nature, which is of key significance for understanding the geodynamic evolution of East Asia in the Mesozoic. Such interpretation is consistent with structural features of the troughs (migration of basin axis inward the continent with time, stratigraphic rejuvenation in the same direction), which are typical of foreland basins regarded as analogues of foreland (marginal) troughs. Obtained data indicate that orogenic processes responsible for the formation of the Mongol-Okhotsk fold belt began in the Early Jurassic.

New data on geochemical features of the Lower Paleozoic terrigenous rocks in the Mamyn terrane (eastern Central Asian Fold Belt) and U–Pb geochronological studies of the detrital zircon from these rocks are presented. The obtained results suggest the following conclusions. 1. At present, the Kosmataya sequence includes different age Lower Cambrian terrigenous–carbonate and Lower Ordovician terrigenous rocks or represents Lower Ordovician olistostromes including limestone blocks with the Lower Cambrian fauna. Lower Ordovician terrigenous rocks were formed in an island arc or active continental margin, mainly, owing to the erosion of Cambrian–Early Ordovician plutons and volcanics that are widespread in structures of the Mamyn terrane and weakly reworked by the chemical weathering. 2. The Silurian Mamyn Formation was developed at a passive continental margin. The main sources of clastic material for this formation were the same Cambrian–Early Ordovician igneous rocks as for the Cambrian sequence, with the participation of Early Silurian and Vendian igneous complexes. The obtained data significantly refine concepts about the geological structure of the Mamyn terrane, which is a member of the Argun Superterrane, one of the largest tectonic structures in the eastern Central Asian Fold Belt.

The northern Urals-Okhotsk belt in eastern Siberia constitutes a late Palaeozoic to early Mesozoic orogenic belt. It occupies an axial position amongst the Palaeozoic orogens of Central Asia. The recognition of its nature is crucial for interpreting the evolution of different-age orogenic belts of Asia. A pattern of terrane zoning in the belt is provided in this paper. Accretionary wedge-type terranes are of importance in the structure of the Mongol-Okhotsk belt. Recognition of their accretionary nature is based on their thrust structure, the presence of ophiolites and glaucophane schists, the tectonic convergence of shallow-water clastic deposits with rocks of the oceanic floor, and the combination of MORB and OIB basalts which originally formed in different geodynamic settings. These features were partly overprinted by collisional deformation. Subduction-related magmatic arcs as well as collisional plutonic associations are distinguished on the margins of the belt. Possible models for the evolution of the belt are discussed, and new palaeomagnetic data are presented and analyzed. Palaeomagnetic aspects in the development of the eastern part of the Central Asian Orogenic Belt are considered from the beginning of the Mesozoic. A palinspastic profi le of the eastern part of the Mongol-Okhotsk belt along the 126 degrees E meridian for 180 Ma and magneto-tectonic reconstructions for 240, 180, and 140 Ma are presented. The Mongol-Okhotsk belt is a typical example of continental collision, resulting from the Siberian craton moving from a polar latitude southwards, simultaneously rotating clockwise, and the North China craton moving in the opposite direction. Smaller continental blocks, such as Bureya, Argun-Mamyn, and Khanka, were essential for the structure of the belt. A specific feature of this belt is a combination of products of magmatism of different geodynamic settings (rifting, subduction, intra-plate setting).

The results of Sm-Nd isotope geochemical investigations of the Paleozoic terrigenous sequences of the Oldoi terrane and U-Pb dating of detrital zircons by the LA-ICP-MS technique showed that the clastic material was mainly derived from Late Precambrian granitoids and Early to Middle Paleozoic granitoids and volcanics, which were formed owing to the reworking of the Late Precambrian continental crust. During the Silurian, the main source of terrigenous material in the sedimentation basin was the erosion of Late Precambrian and Early Paleozoic granitoids. In the Devonian, provenances became more diverse, and the sedimentation basin was additionally supplied by the decomposition products of Middle Paleozoic granitoids and silicic volcanics. The age ranges obtained for detrital zircons from the sandstones of the Middle-Late Devonian Oldoi Formation and the Early Carboniferous Tipara Formation are almost identical to the stratigraphic ages of the formations, which indicates that terrigenous sedimentation in the Oldoi terrane had been accompanied, at least since the Middle Devonian, by vigorous magmatic activity and occurred in an environment of a mature island arc or an active continental margin.

The article describes tectonics and the deep structure of the lithosphere in the eastern fragment of the Mongol-Okhotsk orogenic belt according to results of analysis of the geological and geophysical database. With account of palinspastic reconstructions, the model is developed to show the most probable paleogeodynamics of the lithosphere in the Mongol-Okhotsk orogenic belt and its heterochronous terrains.

Исследованы основные геохимические особенности палеозойских терригенных отложений Ольдойского террейна восточной части Центрально-Азиатского складчатого пояса. Полученные данные свидетельствуют о том, что среди основных источников сноса для этих отложений доминировали породы кислого состава – граниты и рециклированные осадки. Исходя из геологической ситуации, одним из возможных источников обломочного материала могли являться раннепалеозойские гранитоиды, выявленные в пределах тектонических блоков среди силурийских и девонских терригенных комплексов. Анализ стандартных дискриминационных диаграмм позволяет предположить, что на начальных этапах осадконакопление проходило в обстановке пассивной континентальной окраины, а на завершающих – в обстановке островной дуги или активной континентальной окраины. Эти выводы хорошо согласуются с геологическими данными, в частности, с наличием прослоев и линз вулканических пород в осадках среднего – верхнего девона, развитием в пределах рассматриваемого региона гранитоидов с возрастом 386+/–10 млн. лет и 371+/–5.5 млн. лет. С учетом геодинамических реконструкций смена геодинамических обстановок соответствует времени заложения Норовлинской окраинно-континентальной магматической дуги.

The analysis of the major and trace element geochemistry of Paleozoic terrigenous sediments from the Oldoi terrane, eastern Central Asian orogenic belt, supports a predominantly felsic source consisting of granites and recycled sediments. The geological data suggest that detrital material could be derived from Early Paleozoic granitoids, which were identified within tectonic blocks in the Silurian and Devonian terrigenous successions. The analysis of conventional discrimination diagrams indicates that the initial stage was marked by deposition along a passive continental margin, which continued in island-arc or active continental margin environments. This interpretation is consistent with geological evidence, such as the presence of volcanic interlayers and lenses in the Middle-Late Devonian successions and granitoids with ages of 386 +/- 10 and 371+/- 5.5 Ma. The timing of changes in geodynamic settings constrained by tectonic reconstructions corresponds to the age of the inception of the Norovlya continental-margin magmatic arc.

This article contains the first data on the chemical composition and tectonic conditions of deposition of Paleozoic terrigenous sediments of the Ols’doi Terrain located in the eastern portion of the Central Asian Fold Belt. The data obtained suggest that at the initial stage deposition of sediments took place in the environment of a passive continental margin, while at the final stage it occurred in the environment of an island arc or an active continental margin. Based on all geological data available, the change of the geodynamic settings corresponds to the time of the formation of the Norovlya margin-continental magmatic arc.

Permian deposits in the Transbaikal region within the Mongol–Okhotsk belt and adjacent areas have been studied. The characteristics of the Permian marine and continental formations are documented, and our present understanding of the stratigraphy is presented. The constitution of the regional stratigraphic units, or horizons, is specified, and their paleontological characteristics are stated. The correlation of the horizons with the Permian global chronostratigraphical scale is rather tentative, and has been made possible only by comparison with the well-characterized sections of Northeast Russia. Incomplete faunal distribution in the sections of the Transbaikal region makes it difficult to distinguish uninterrupted zonal sequences. However, the presence of characteristic associations and often, of index-species of biozones recognized outside the Transbaikal region, makes it possible to trace and date these biostratigraphic units. The contradiction between paleobiogeographic and paleomagnetic evidence is noted, the Permian biota being represented by Boreal faunas and Angaran floras suggestive of temperate latitudes, while paleomagnetic data seem to indicate tropical latitudes for the Transbaikal Region during the Permian.