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The palingenic calc-alkaline granitoid massifs of the Olekminsky complex form a magmatic belt stretching within the Western-Stanovoy terrane in the northeastern direction for more than 700 km. New U-Pb LA-ICP-MS dates for zircons from the granodiorites of the Marekta-Bereinsky massif of the Olekminsky complex and the granodiorites of the Yamninsky massif of the Krestovsky complex were obtained, amounting to 371±4 Ma and 364±5 Ma, respectively. These geochronological data are well consistent with the 355–358 Ma ones, therefore suggesting the Late Carboniferous age of quartz-diorite-granodiorite-granite rocks of the Olekminsky complex. However, these dates are not correlated with the existing legends of geological maps covering the area of the Western-Stanovoy structural-formation zone or the Western-Stanovoy terrane, as the intrusive formations of the Olekminsky complex are dated as the Early Paleozoic. In addition, new geochronological data call into question distinguishing of a separate Early Paleozoic Krestovsky granitoid complex.

The paper presents the first results on Sm-Nd isotopic-geochemical studies of the Paleozoic sedimentary rocks in the Nora-Sukhotino terrane at the northeastern flank of the South Mongolia-Khingan orogenic belt.According to the studies, the sedimentary rocks of the Zeya-Selemdzha and Amur fragments of the Nora-Sukhotino terrane are characterized by the two-stage Mesoproterozoic Nd-model age (TNd(DM2)=1.62–1.08 Ga) at negative εNd(0)=–9.5…–3.0 and εNd(T)=–5.8...–0.2. Based on previous geochemical and isotopic (U-Pb, Lu-Hf) studies of sedimentary rocks of the Nora-Sukhotino terrane, as well as on the available models for the formation of the South Mongolia-Khingan orogenic belt, it can be assumed that most of the Paleozoic sediments of the Nora-Sukhotino terrane were carried from the Mamyn terrane of the Argun superterrane with the participation of the island arc formations.

The intraplate alkaline-granite magmatism essentially contributes to formation of rare-metal strategic raw materials. In the Major Sayan Fault of the East Sayan Mountains, the rocks of the Zashikhinsky (Pz3) massif were studied through the isotope-geochemical analysis to identify probable sources of alkaline-granite magma and mechanisms of their evolution resulting in ore accumulations, up to the formation of Nb-Ta deposits. The Nd isotopic characteristics of its alkaline granites were obtained for the first time. Together with the results of mineralogical and geochemical studies, they were applied for modeling its formation, in which crystallization differentiation of alkaline granite melts proceeds simultaneously with their assimilation of the enclosing granite-metamorphic formations.

The isotopic data showed that there are two stages distinguished in the Cenozoic history of the Darkhad depression volcanic activity, the Late Oligocene initial stage (~28.0–26.6 Ma) and the final Late Miocene – Early Pliocene stage (~5.8–4.2 Ma). It has been stated that the rocks of the initial stage are only represented by trachybasalts; however, among the final-stage basaltoids there are series of shield-volcano hawaite-basanite-phonotephrite rocks and compex trachybasaltic "valley" lava flows, the formation of which is the last stage in the territorial volcanic evolution. It has been shown that the initial-stage trachybasaltic andesites are characterized by their enrichment of TiO2, P2O5, Sr, Zn, Ga and low concentrations of Al2O3, MnO, CaO, Sc and HREE (La/Yb=27.2–30.2). Basaltoids of the final stage have a similar rare-element distribution and show an increase in the contents of TiO2, Al2O3, P2O5, LILE, HFSE, Th, U and in the degree of fractionation of REE (La/Yb from 12.2 to 20.9) towards the rocks alkalinity enhancement. Modeling of eclogite, pyroxenite and peridotite melting processes in the La/Yb – Sm/Yb system shows that trachybasaltic andesite melts could be formed at ~7–8 % melting of eclogitic matter or at ~10–11 % melting of Grt-containing pyroxenites, with trachybasalt formed at ~3 % melting of Grt-containing peridotites. The composition distribution of rocks in coordinates (Mg# – Fe/Mn) indicates that the parental magmas are the initial-stage trachybasaltic andesite magmas as well as the Early Pliocene trachybasaltic "valley" lava flows. Sr, Nd, Pb isotope characteristics of the Darkhad depression basaltoids show significant shift of isotopic ratios in time towards the relatively enriched mantle as compared with the depleted MORB mantle. The initial formation of trachybasaltic andesite melts occurred in the Late Oligicene at the pre-rift stage of the territory development involving metasomatized mantle matter, with the pyroxenite or eclogite component contained in the magma formation source. The origin of trachybasalt magmas of the final stage is associated with the processes of decompression melting of peridotites in a weakly metasomatized lithospheric mantle at the rift stage of the Darkhad structure development.

The article presents new data on ages (U-Pb zircon dating, SIMS SHRIMP-II) and chemical compositions of rocks from gabbro-granitic and granite-leucogranitic magmatic associations. These rocks preceded the formation of Li-enriched spodumene pegmatites of the Tserigiyngol-Burchin ore cluster (Russian: ЦБРУ), one of the main clusters in the South Sangilen pegmatite belt (SSB) located in the Tuva-Mongolian massif being a part of the Central Asian Fold Belt. We investigated the rocks from the Upper Tserigiyngol, Uchuglyk and Temenchulu plutons, and pegmatites from two neighbouring fields. We distinguish three impulses of granitic magmatism (517±7, 508±7, and 488±6 Ma), which are attributed to different stages of the Early Paleozoic collision orogeny (520-480 Ma). The period when the Li-enriched pegmatites were formed (494±7 Ma) is close to the magmatism impulse at 488±6 Ma. Differences are discovered in compositional and isotopic (Sm-Nd) features of granites dominating at the following stages of collisional orogeny: (1) early collision (517±7 Ma) – I-type granites, eNd(T)=0–1.5, TNd (DM-2st)=1.2–1.1 b.y., and (2) late collision (488±6 Ma) – A-2-type granites, eNd(T)=–3.0…–1.6, TNd (DM-2st)=1.5–1.4 b.y., which are due to different sources. Our study shows that facies transitions are absent between the late-collision granites (488±6 Ma) and the spodumene pegmatites from the Tserigiyngol-Burchin ore cluster (494±7 Ma), although these rocks are close in age. In terms of geochemical features, the spodumene pegmatites from the cluster are strongly different from both the late-collision granites and spodumene pegmatites from other SSB fields, including the large Tastyg lithium deposit. We have analysed the role of interactions between the crustal and mantle materials in the formation of granitoid sources in the Tserigiyngol-Burchin ore cluster, and described their evolution in time and the influence on the pegmatite rare-element specialization.

The Eastern Sayan ophiolites (1020 Ma) of the Tuva-Mongolian microcontinent are believed to be the most ancient ophiolite of the Central Asian Orogenic Belt [Khain et al., 2002].

There are several geodynamic models of the Central Asian Orogenic Belt (CAOB) development [Şengör et al., 1993, Zorin, 1999; Parfenov et al., 1999, 2003; Willem et al., 2012; and others]. The Mongol-Okhotsk Orogenic Belt (MOB) represents important part of CAOB. All geodymanic models of Late Riphean to Paleozoic structures of CAOB emphasize significance of subduction processes along Northern Asian craton margin at that time. Collage of CAOB terrains formed as a result of accretion of island arc, accretionary wedge, turbidite, and continental margin terrains to the Siberian paleocontinent.

The Neoproterozoic to Cenozoic collage of the Central Asian Orogenic Belt is well-known to include Precambrian continental blocks and microcontinents traditionally attributed to rifting of Siberia or Gondwana prior to CAOB assembly that significantly contributed into the geochemical and isotopic composition of younger subduction- and accretion-related crustal lithologies via processes of crust-mantle interaction and crustal recycling.

There have been petrographic, geochemical, geochronological (Rb-Sr, Ar-Ar) and isotopic (Sm-Nd) studies done on the metamorphic formations of the Kharamatolou structure of the Polar Urals, which were usually assigned to the Precambrian. The temperatures of metamorphism have been shown to range from 450 to 626 °C, and the pressures – from 3.7–9.1 kbar once PT-conditions reached the amphibolite facies. The amphibolites of the Kharamatolou formation are geochemically divided into two groups. According to the distribution spectra of lanthanides and Nd isotope composition, one group has the characteristics similar to depleted N-MORB basalts εNd(0)=+7.0, and another group – those similar to moderately enriched E-MORB basalts εNd(0)=+(4.5–2.4). It has been found that the Kharamatolou structure is probably composed of the Early to Middle Paleozoic continental rise deposit of the Russian Platform, which passed the main stage of folding and metamorphism in the Late Devonian (Rb-Sr, 366±11 Ma). The gabbro-ultrabasic Ray-Iz and Voykar-Synya massifs have been shown to be one during most of their Pre-Triassic history. Now these ultrabasite massifs are separated by the young (Triassic) Kharamatolou uplift which is an erosive-tectonic semi-window where ultrabasic rocks of the Polar-Ural belt are exposed at the base of the thrust fault. The Kharamatolou structure is one of the transverse uplifts of the Urals which probably resulted from the Middle to Late Triassic compression therealong. As a result of the Middle to Late Triassic uplift of the Haramatolou metamorphites, the overlying ultrabasites were washed away by erosion. The mélange serpentinites observed in the center of the Kharamatolou structure are uneroded remnants of the link that once existed between the Ray-Iz and Voikar-Synya massifs. This significantly increases the metallogenic potential of the Voikar-Synya massif, as the Ray-Iz hosts the largest known chromite deposits in Russia.