The article presents the first results of isotope-geochemical (Sm‒Nd, Rb‒Sr) and geochronological (U‒Pb LA-ICP-MS) studies of Cambrian volcanosedimentary strata (Terek and Ezhim formations) of the Systighem terrane (Central Tuva). It was established that the origin of the primary basaltic magmas of the Terek and Ezhim formations is associated with partial melting of a mantle source (OIB type), metasomatically worked through by processes associated with contamination during melting of a dehydrated slab. Their formation occurred in rift basins marking extension processes in the rear part of the accretionary complex with transitional or continental crust against subduction of Paleo-Asian Ocean crust underneath it. The formation of the volcanosedimentary strata of the Terek and Ezhim formations occurred nearly simultaneously in the interval 512‒510 Ma. Similar isotope-geochemical characteristics of the composition of volcanic rocks of the studied formations (εNd(510) = +3.9 to –0.45 and εNd(510) = +4.5 to –0.23) and the time of their formation indicate a single sequence, which undergoing folding or other tectonic processes was divided into disconnected fragments, deformed, and displaced relative to each other by horizontal movements during accretion–collision events. On the modern erosional section, they are represented by a series of combined tectonic plates, altered to varying degrees, thrust upon each other and, on an existing and buried continental block.

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060144

The research was focused on the Mara–Kamenka–Uvat interfluve of the Biryusinsky ledge of the Siberian Platform, where more than half a century ago, during prospecting works for manganese, the Marа paleovolcano was identified. However, specific volcanogenic-sedimentary rocks were considered as a part of the Karagas sedimentary series of the Late Riphean. Our mineralogical and petrographic studies have allowed us to establish the wide distribution of high-potassium pyroclastics, ignimbrites, and trachybasalts, indicating a subaerial explosive volcanic nature of the Mara volcano. The age of high-potassium volcanism has been determined based on U–Th–Pb zircon dating as 640 Ma. Lu–Hf isotope systematics of zircon indicate a relation of these volcanic rocks with mantle-derived magmas. The composition and time of formation of the studied rocks do not allow us to correlate them, as previously thought, with sedimentary Late Riphean quartz and quartz-feldspathic sandstones of the Karagas sedimentary series and dolerites of the Nersa intrusive complex. The specific mineralogical and petrographic features of the studied rocks make them suitable as a regional stratigraphic mark.

This work focuses on petrological-and-geochemical features, as well as age of dolerites widespread within the basins of the Mara, Kamenka and Uvat rivers. The isotope geochronological data acquired for baddeleyite allowed referring origination of these rocks to the time interval 1600–1620 Ma, interpreted as the time of their emplacement. It was ascertained, that the age of dolerites represents particular geological event proceeding independently of formation of Neoproterozoic Nersinsk gabbro-dolerite complex. The Sm-Nd isotope signature indicates that parent melt generated from the metasomatic lithosphere mantle.

The studies are focused in the Mara–Kamenka–Uvat interfluve of the Biryusa Uplift of the basement of the Siberian Platform, where the Mara paleovolcano was recognized during the prospecting works for manganese more than 50 years ago. The specific volcano-sedimentary rocks are considered in the structure of the Late Riphean Karagas Group. Our mineralogical and petrographic studies allowed us to establish abundant high-K pyroclastic rocks, ignimbrites, and trachybasalts, which indicate a subaerial explosive character of the Mara volcano. The age of high-K volcanism of 640 Ma is based on U–Th–Pb dating of zircon. The Lu–Hf isotope systematics of zircon indicates a link of volcanism with mantle magmas. The composition and the period of the formation of rocks prevent their correlation (as was considered before) with sedimentary Late Riphean quartz and quartz–feldspar sandstones of the Karagas Group and dolerites of the Nersa intrusive complex. Specific mineralogical–petrographic features of rocks allow their use as a regional stratigraphic reference.

The Proterozoic - Paleozoic tectonic history of the northern Central Asian Orogenic Belt (CAOB) remains controversial. The Khamsara Terrane located in the northern segment of the CAOB near the Siberian Craton plays a crucial role in reconstructing of processes associated with the evolution of the Paleo-Asian Ocean (PAO). This terrane mainly consists of metasedimentary and metavolcanic rocks (Shutkhulai, Balyktygkhem and Mongosha formations) intruded by mafic and granitic rocks, that preserve an abundant record of tectonic processes through the Proterozoic - Paleozoic. This paper presents a whole-rock geochemical data, U-Pb and Ar-Ar ages for igneous and metamorphosed rocks from the Khamsara Terrane with the aim of constraining its tectonic evolution. The youngest detrital zircon U-Pb ages constrain the depositional time of the Shutkhulai and Mongosha formations after 680 Ma and 640 Ma, respectively. Detrital zircons with U-Pb age between 950 and 700 Ma, and subordinate peaks at 790 and 720 Ma indicate formation of the Khamsara metasedimentary rocks through erosion of the magmatic rocks that could be caused by rifting process related to Rodinia supercontinent break-up. The zircon UPb age of -480 Ma obtained for granites allows timing their emplacement and the reactivation of the Main Sayan Fault during convergence of the Khamsara Terrane with other terranes and final closure of the PAO. The zircon U-Pb age of igneous rocks and the biotite Ar-Ar age of metamorphosed rocks document a -310-270 Ma tectonomagmatic event maintained by the activity of a mantle plume beneath the Khamsara Terrane and the adjacent CAOB areas.

At the boundary of the Meso- and Neoproterozoic, Grenville collision events were widely manifested on the margins of ancient continental blocks. Most of the sedimentary sequences that had accumulated by that time had undergone significant thermal–metamorphic changes. In many ways, this is the main reason for the lack of isotopic data for carbonate deposits in the interval of 1200–900 Ma in world practice. Sr–isotopic composition in carbonate rocks with an age of 980–920 Ma was determined in the only section of the World – the Huainan Formation of the North China Platform with accumulation time determined by U–Pb dating of detrital zircon grains. In the upper part of the Nizhny Tunguska suite of the Turukhansk uplift, among carbonate deposits, we established the presence of altered volcanic rocks, as well as weathering crust products along them – poor bauxite and chamosite ores. Based on U–Pb zircon isotope dating, the age of the volcanic rocks is 964 Ma. For the least altered limestones of the upper part of the Nizhny Tungusska Formation, received 87Sr/86Sr values are 0.70532–0.70578, which are close enough to those found in the rocks of the Huainan Formation. Geochronological age of the studied limestones gives us more correct data. These data can be used to refine the previously proposed configuration of the Sr–isotopic composition variation curve in the Early Neoproterozoic. The Nizhny Tunguska Formation is the only carbonate section of the Early Neoproterozoic in the world with correctly geochronologically substantiated dating (based on zircon from subsynchronous volcanic rocks). This compares favorably with the Huainan formation.

The isotope–geochronological and geochemical data on the age and composition of rocks of the Butugol Block, located in the eastern part of the Tuva–Mongolian microcontinent of the Central Asian Orogenic Belt, have been obtained. It has been established that the protolith for gneisses is, in one case, volcanic rocks with an age of 1009 ± 8 Ma, and in the other case, potassium meta-sedimentary rocks accumulated in continental marginal basins. The protolith of metavolcanogenic rocks of this complex were formed at the turn of the Mesoproterozoic and Neoproterozoic on the already formed crust, while the metasedimentary rocks were formed owing to the Mesoproterozoic, more rarely Paleoproterozoic and Archean, continental provenances. It has been established that the development of the Butugol metamorphic complex (Butugol Block) differs from the development of other blocks of the Earth’s crust included in the composite Tuva–Mongolian microcontinent.

The age of sedimentation (530–520 Ma) of the Teregtig Formation of South Tuva is estimated on the basis of U–Pb dating of detrital zircon grains from terrigenous rocks and Sr chemostratigraphy of carbonate rocks. It is shown that granitoids with an age of 580 Ma were the main source of detrital zircon. The presence of a representative Precambrian detrital zircon population indicates the deposition of sediments of the Teregtig Formation within the continental crustal block with a long evolution. During the accumulation of coarse-grained rocks of the Teregtig Formation, this part of the eroded area also comprised rocks of the Agardag ophiolite massif, which is evident from numerous angular clasts of olivine, pyroxenes, and Cr-spinels in the conglomerate matrix.

Multidisciplinary geochronological, isotopic, chemical, and facial studies in the Malyi Karatau Range (MK) of South Kazakhstan elucidate the Precambrian stratigraphic framework and evolution of the Ishim Middle Tianshan microcontinent (IMT) in the western Central Asian Orogenic Belt. Detrital zircon and apatite U-Pb ages for siliciclastic rocks and chemostratigraphic Sr-C isotopic data for carbonates indicate that they deposited during 800-730 Ma. The sediments are dominated by deeper marine facies in the southwest and shallow marine facies in the northeast. According to paleocurrent indicators, the main provenance located to the west of the basin. Based on the detrital zircon age spectra, the source terrane represented a Paleoproterozoic to Archean crustal block, reworked by an early Neoproterozoic c. 850- 720 Ma continental arc. Erosion of Archean and Paleoproterozoic crust is also evidenced by negative eNd values for the sandstones. The petrographic and chemical compositions of the sandstones are consis-tent with a continental arc source; however anomalously high concentrations of chromium in some lay-ers point to the presence of ultramafic rocks in the source terrane. The ages of metamorphic zircons indicate a high-grade metamorphic event at provenance at c. 2.0 Ga and the ages of detrital apatites sug-gest a reset of U-Pb isotope system in apatite at c. 1.8-1.9 Ga. In the early Neoproterozoic, the MK located between the continental arc in the west and the oceanic basin in the east and represented a fore-arc basin. The similarity of the Precambrian magmatic and metamorphic histories and sedimentary facies indicates that the IMT, the Tarim and Yangtze cratons constituted a single Precambrian Ulutau-Tarim-Yangtze Continent (UTY). Judging from the ages of continental arcs that evolved on the northern and southern sides of the UTY, it represented an independent continent at c. 950-840 Ma and was incorpo-rated in Rodinia at c. 830-820 Ma.(c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The sedimentation interval (530–520 Ma) of the Teregtig Formation deposits in southern Tuva is estimated based on U–Pb dating of detrital zircons from terrigenous deposits and Sr-chemostratigraphy of carbonate rocks. The main source area for clastic material, containing a large amount of detrital zircon grains, were rocks with an age of 580 Ma. The presence of a wide diversity of Precambrian detrital zircons indicates that sedimentation of the Teregtig Formation took place within a block of continental crust with a long evolutionary history. The presence of numerous chromites in their matrix indicates that the rocks of the Agardag ophiolite complex were also part of the eroded land during the accumulation of conglomerates of the Teregtig Formation.

The results of geochemical, isotope-geochemical (Sr, C, O) surveys of the Kinterep Formation carbonate deposits of Northwestern Salair and U-Pb dating (LA-ICP-MS) of zircons were given. Carbonate rocks represented by pure limestones are characterized by normal values of δ18OSMOW from 19.8 to 23.8 ‰ and δ13 CPDB from –0.7 to +0.9, the isotopic composition of Sr (87Sr/86Sr ratio) varies in a narrow range from 0.708486 to 0.708582.Using Sr and C isotope chemostratigraphy and U-Pb dating of zircons, age limits (525-510 Ma) were determined for the formation time of carbonate deposits of the Kinterep Formation. The first data of isotope chemostratigraphy in combination with the results of geochronological studies made it possible to compare the limestones of the Kinterep Formation of Northwestern Salair with carbonate sections of Siberia and Central Asia.

There have been presented the results of the study of a thick (no less than 2–3 km), extended (for more than 200 km) volcanogenic formation (Tsetsen-Uul or Yargait) in the south of the Zavkhan terrane of the Central Asian fold belt. The formation is an assemblage of frequently intercalating effusive rocks of the subalkaline basalt-andesite-dacite-rhyolite series, their tuffs, tuffites, ignimbrites, and terrigenous rocks. Felsic rocks dominate over basites, and tuffogenic rocks dominate over effusives. There is some evidence that the formation emerged in a subaerial setting, with explosive eruptions, and the petrogeochemical features of the effusive rocks are typical for subduction environment. The felsic effusive rocks have high negative ε Nd from –11.5 to –12.8 and Early Precambrian model age T Nd (DM)=2.4–2.5 Ga, which indicates the presence of an ancient crust at the depth and its involvement in magma. The evidence supports the formation of volcanic rocks within an active continental margin. The continental-margin formation stage ranges from ~860 Ma to ~780 Ma based on the LA-ICP-MS U-Pb dating of zircons. The Tsetsen-Uul (Yargait) formation is similar in structure and composition to the Zavkhan formation of the Zavkhan terrane and the Sarkhoi group of the Tuva-Mongolian massif, and partially overlaps them in formation time. It is concluded that all three volcanogenic formations emerged in the same geodynamic setting and in the same time interval, and are the fragments of a continental volcanic arc belonging to both Zavkhan and Tuva-Mongolian paleomicrocontinents.

A comprehensive study of the stratotype section of the Kinterep formation of the North-Western Salair was carried out, including geochemical and isotope (Sr, C, O) studies of carbonate rocks, and U-Pb dating (LA-ICP-MS) of igneous zircon crystals from tuffites. The studied carbonate rocks are pure limestones with Mg/Ca less than 0.007 and a low proportion of insoluble residue (average 5 %). Kinterep limestones are characterized by δ18OSMOW values from 19.8 to 23.8 ‰ and δ13СPDB values from –0.7 to +0.9. The Sr isotope composition in limestones of the Kinterep formation varies in a narrow range of 87Sr/86Sr values between 0.70851 and 0.70859. Comparison of the obtained isotopic characteristics (87Sr/86Sr and δ13СPDB) of Kinterep formation limestones with the generalized global 87Sr/86Sr variation curve and δ13СPDB values in the pale-ocean suggests two equally probable interpretations of the time of accumulation of Kinterep formation limestones: 550–540 and 525–510 Ma. U-Pb dating of magmatic zircon crystals from tuffite, which forms an interlayer among limestones of the Kinterep formation, showed the age at the boundary of ~515 Ma. Thus, using a combination of isotope (Sr, C) chemostratigraphy of carbonate rocks and U-Pb dating of igneous zircon crystals from tuffites syngenetic to limestones, the age limit of 525–510 Ma was established for the time of the formation of the Kinterep formation of the Salair basin. Carbonate rocks of similar age and similar features of the isotopic composition are known in neighbouring areas (for example, the Kuznetsk Alatau) and in regions of the Siberian Platform and microcontinents of Central Asia (Tuva-Mongolian and Dzabkhan) spatially distant from the Salair basin.

The geochemical and isotopic (Nd, Sr) characteristics of felsic volcanic rocks of the Pecherkinskaya Formation in the northwestern part of the Salair Ridge were studied. These rocks are closely associated with industrially significant deposits and manifestations of gold- and silver-bearing pyrite-polymetallic formations with potentially gold-bearing weathering crusts on them. The study of the material composition of unaltered volcanic rocks of the Pecherkinskaya Formation is necessary for the reconstruction of the conditions of their formation, which contributes to estimation of the mineragenic potential of this formation and the conditions during the accumulation of ore matter. Felsic volcanic rocks of the Pecherkinskaya Formation are an extreme member of the basalt-plagioryolite series, have an extremely high-sodium type of alkalinity with a low potassium content, are calcareous and characterized by high silica contents, low iron content, have low REE concentrations, are enriched in Pb and U and depleted in Ta and Nb, are characterized by high values of εNd (t) (+6.36) and primary ratio 87Sr / 86Sr (0.706977). The REE distribution spectra show a low degree of fractionation with a pronounced negative "europium anomaly". The geochemical composition of the Pecherkinskaya Formation volcanic rocks indicates that primary magmas were formed by partial melting of rocks of the lower continental crust at a pressure of ~ 8 kbar in equilibrium with Hbl + Cpx + Pl ± Opx restite and a temperature of ~ 750-790 ° C. The isotope-geochemical characteristics indicating the participation of depleted mantle in the source are probably inherited from the juvenile crust, the rocks of which could have been formed as a result of differentiation of mantle magmas. Geological and geochemical features of felsic volcanic rocks of the Pecherkinskaya Formation are characteristic of igneous rocks formed under conditions of oceanic arcs.

—The Tuva segment of the Central Asian Orogenic Belt is characterized by the ubiquitous presence of conglomerates few tens of meters to a kilometer in thickness in early Paleozoic volcanosedimentary sequences. We present the first results of geochemical, isotopegeochemical (Sm–Nd and Rb–Sr), and U–Pb geochronological studies of granitoid boulders and pebbles from the conglomerate sequence of the early Cambrian Bayan-Kol Formation of the Systyg-Khem depression. These studies made it possible to establish several sources of clastic material as a result of the destruction of granitoids of different ages and isotope-geochemical compositions. At least two complexes of granitoids were denuded in the pre-Ediacaran tectonic block in the early Cambrian: (1) middle Ediacaran (~590 Ma) and (2) early Ediacaran (~630 Ma); the latter resulted from the melting of pre-Ediacaran island arc crust formed from a depleted mantle source (εNd(T) = +8.0 to +8.6). At present, no granitoids of this age and with such isotope-geochemical characteristics have been found within the Tuva segment. Probably, the granitoid complexes reconstructed from the results of study of clastic conglomerates are eroded or buried beneath younger deposits and do not expose. Thus, the study of clastic conglomerates from the Bayan-Kol Formation provided the first information about the Precambrian history of the tectonic block whose destruction led to the accumulation of this terrigenous sequence.

Isotope study of ore-bearing rocks at Fe–Mn rift deposits of the Atasu and Zhezdy (Dzhezdy) ore districts in Central Kazakhstan has been carried out for the first time. The Atasu felsic effusive rocks (Ushkatyn-1 deposit), synchronous to ore genesis, were formed at the boundary between the Frasnian and Famennian (373 ± 4 Ma). The Zhezdy ore-bearing gravelites began to accumulate not earlier than the end of the Early Devonian (after 400 Ma), but before the felsic volcanism impulse at the turn of 370 Ma. The data obtained can be indicative of asynchronous Fe–Mn deposition in the Zhezdy and Atasu ore districts.

Based on the dating of metamorphic and igneous rocks of the northeastern part of the Khamsara terrane, the main stages of tectono-magmatic activity at the border of two large structures—the Central Asian fold belt (CAFB) and the Siberian craton—have been established. The formation of the initial volcanogenic–sedimentary formations of this terrane, which mark the continental-marginal stage of development, took place in the range of 680–640 Ma. The age of accretion–collisional events in the CAFB fragment adjacent to the Siberian platform is fixed by the intrusion of postcollisional granitoids with an age of 480 Ma. Subsequent manifestations of Ordovician intraplate volcanism (464–462 Ma) are associated with the decay of the collisional orogen under the conditions of incipient rifting. Another stage in the development of this block is also associated with the processes of intracontinental extension and is represented by Late Paleozoic basic volcanism with an age of 267 Ma. The first established manifestations of rifting processes of different age levels within the fragment of the CAFB considered are associated with its location on the border of large inland structures separated by faults that retain their activity for a long time.