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–Anorthosites of the Olonkhuduk pluton of the Central Asian Orogenic Belt are dated at 1772 ± 1 Ma (ID TIMS U-Pb zircon method). Similar age estimate (1784 ± 10 Ma) was previously obtained for anorthosite of the Khungilingol pluton from the Ider block of the Tarbagatai terrane. These data indicate a significant time gap (70–60 Ma) between the collision that formed the Early Precambrian blocks of the Baidaric and Tarbagatai terranes in the range 1860–1850 Ma and the emplacement of the anorthosites. The termination of accretion-collision processes and consolidation of the Early Precambrian block of the Baidaric terrain are marked by the postkinematic subalkaline granites with an age of 1825 ± 5 Ma. Geochemically, the anorthosites of the Olonkhuduk and Khungilingol plutons are similar to the typical anorthosites of ancient cratons. Sm-Nd isotopic data indicate a mixed source of these anorthosites: juvenile mantle component of Paleoproterozoic age and crustal component of Neoarchean age. It can be assumed that the primary mafic magma of the anorthosites experienced a significant crustal contamination. Based on the similar geologic setting, age, and composition, the anorthosites of the Olonkhuduk and Khungilingol plutons can be ascribed to a single within-plate complex. The age values obtained for the anorthosites coincide with the estimated age of rift magmatism in the North China craton at 1.8–1.75 Ga and the emplacement time of mafic dikes swarms at 1778 ± 3 Ma (SIMS U-Pb method). Thus, the considered Early Precambrian blocks by the end of the Paleoproterozoic (about 1900–1850 Ma) could be a part of the Columbia supercontinent (Rogers and Santosh, 2002).

Granite–porphyries of the Yazovka complex occur in the northern part of the Riphean Baikal–Patom fold-thrust belt within the Tonod Uplift of the Early Precambrian basement. The geochronological (U–Pb), isotope-geochemical (Sm–Nd), and geochemical studies have shown that the rocks of this complex belong to A-type tin-bearing granites of the age of 709 ± 7 Ma. Initial magma of these granites was formed from the mixed Early Precambrian crustal and mantle source in the intraplate geodynamic setting. This tectonic event was global in nature and manifested the Late Riphean impulse of the lithospheric extension, which was associated with breakup of the supercontinent Rodinia under the influence of a mantle superplume.

High-precision dating of granitoids is of key significance for age identification of the main stages of crust formation in various blocks of the continental crust. Here we demonstrate geochronological results for of the Kedrovskii diorite–granodiorite massif localized within the South Muya block of the Baikal–Muya accretionary terrane (BMT) (Eastern Siberia) among Neoproterozoic gabbroids of the Kedrovskii complex and metasedimentary rocks of the Kedrovskaya Formation. The results of U–Pb (ID TIMS) and 39Ar/40Ar geochronological studies of the Kedrovskii massif are discussed. The crystallization of the massif (781 ± 3 Ma) occurred at an early stage of formation of the Proterozoic continental crust of the BMT during accretion of Baikalids with the Siberian craton margin. A later thermal event (626 ± 11 Ma) that took place at the Ediacaran stage of the BMT evolution resulted in the formation of a series of transverse biotite–quartz–feldspar veins cutting through the granitoids of the Kedrovskii massif. The geochronological data obtained show that the gold mineralization of the Kedrovskoe deposit (273 ± 4 Ma) was not generated by granitoids of the Kedrovskii massif.

The article presents the results of U-Pb in zircon and Nd-isotope study of the adakite granites of the Goryachinsky pluton, exposed along the Baikal coast in the section of termination of the package of shear tectonic plates of the Baikal-Muya belt. The Early Cambrian age of granitoids, which is unusual for the Northern Baikal region, is 545 ± 6 Ma. According to the authors, new geological and isotopic data indicate the formation of the studied granitoids at the final stage of the Late Baikal shear tectogenesis, which caused the manifestation of adakite magmatism within the Baikal-Muya belt.

The Early Caledonian folded region of the southern framing of the Siberian platform, between the Zavkhan and Tuva-Mongolian terranes, contains blocks of the Songino ledge crystalline rocks. In the Bayan Nuur block (southern part of the Songino ledge), the Neoproterozoic (890–780 Ma) Bayan Nuur gneiss-migmatitic and Kholbo Nuur metaterrigenous-volcanogenic complexes are distinguished. The zone of their junction is traced by thrust structures, which are reflected in all structural-material complexes of the Bayan Nuur block. There are tectonic slabs in the junction zone. Their peculiarity is the presence of rocks formed before the formation of thrust gabbro-ultrabasite complex and post-thrust gabbroids and gabbro-diorites. The upper limit of the thrust formation interval is defined by Bayan Nuur pluton granitoids having the age of 790 ± 3 Ma and by gabbroids and anorthosites of Onzula tectonic plate giving the ages of 785 ± 3 and 784 ± 3 Ma. The lower limit of the thrust formation interval is determined by the age of the Bayan Nuur ultrametamorphic granitoid complex (802 ± 6 Ma). Bodies of massive (post-thrust) pegmatoid gabbros and rocks of gabbro-ultrabasite complex possessing clearly manifested thrust-associated structures are recognized in the tectonic slab of the ridge reaching the area of Mount Sant Uul. These rocks are dated at 782 ± 2 and 806 ± 10 Ma, respectively (ID-TIMS). The data indicate that the post-thrust and pre-thrust units cannot be parts of a united layered complex. In turn, pre-thrust units can be considered as paleooceanic fragments in the accretionary structure of the Bayan Nuur block, Songino ledge.

New results of U–Pb zircon and Nd–isotope analyses of the Goryachinskiy Pluton adakite granites have been obtained. The pluton is exposed along the Baikal coast in the section where a section of sheared tectonic sheets of the Baikal–Muya Belt wedges out. The determined Early Cambrian (545 ± 6 Ma) age of the granitoids is unusual in the Northern Baikal region. These new geological and isotopic data are interpreted as an indication of the formation of the granitoids studied at the final stage of the Late Baikal strike–slip tectonics, which caused the pulse of the adakite magmatism within the Baikal–Muya belt.

The Tuva–Mongolian terrane (TMT) of the Central Asian Orogenic Belt is a composite structure with a Vendian–Cambrian terrigenous–carbonate cover. The formation of the northern part of TMT is marked by the granitoids of the Sumsunur Complex with an age of 785 ± 11 Ma. The Sangilen and Khan-Khukhay blocks of its southern part also form a composite structure, which originated during Early Paleozoic (500–490 Ma) low–moderate pressure regional metamorphism reaching amphibolites–granulite facies. The earlier high-pressure metamorphism was established in the Moren Complex of both the blocks. In the Sangilen block, this metamorphism reached conditions of kyanite–garnet–biotite–orthoclase subfacies of amphibolites facies (temperature ~750°C, pressure 9–10 kbar). The upper age limit of this metamorphism is determined by granites with an age of 536 ± 6 Ma, which cut across migmatized biotite gneisses of the Moren Complex. The latter are intruded by the granitoids of the Ortoadir pluton, which were previously dated at 521 ± 12 Ma (U-Pb method, TIMS). Its emplacement predated the Early Paleozoic low–moderate pressure metamorphism, the timing of which is constrained by syn- and postmetamorphic granitoids with ages of 496 ± 4 and 489 ± 3 Ma. The age of 513 ± 4 Ma established for the granitoids of the Ortoadir Complex in the Khan-Khukhay Block more accurately constrains the lower age boundary of collision processes. This determined the amalgamation of the fragments of the high-pressure metamorphic belt with basement and carbonate–shelf cover units of the Tuva–Mongolian terrane, as well as the upper age boundary of early metamorphism. The timing of the main mappable structure of the Khan-Khukhay Block and low–moderate pressure regional metamorphism is marked by the synmetamorphic granitoids with an age of 505 ± 2 Ma. In general, the metamorphic rocks of the Sangilen, Khan-Khukhay, and Kaakhem blocks can be considered as fragments of the Late Ediacaran high-pressure metamorphic belt, which were amalgamated to the western margin of TMT within 515–505 Ma, after emplacement of the granitoids of the Ortoadir Complex, and were reworked by regional Early Paleozoic low–moderate pressure metamorphism.

This paper presents the results of U–Pb isotope–geochronological study on zircons from subalkali gabbros and granodiorites of the Dogaldyn intrusive massif located in the Karalon–Mamakan zone of the Baikal–Muya belt. The ages of 254 ± 2 and 256 ± 1 Ma yielded for rocks of the two main intrusion phases do not differ significantly from each other and correspond to the Late Permian period. The Nd-isotope and geochemical data indicate the relationship between the primary melts of intraplate rocks from the Dogaldyn Massif and various sources, including plume–mantle and ancient crustal ones. The manifestations of Late Permian intraplate magmatic activity in the Baikal–Muya belt could have been induced by the Iberian superplume framed by the Siberian trap province.

The Dotulur alkalic granite and Usugli Depression volcanics (West Stanovoi Superterrane of the Central Asia Fold Belt) have been dated by the U–Pb method, and their geochemistry has been analyzed. The geochemistry of the rocks suggests their intraplate nature. The alkalic granite and volcanics have similar ages of 142 ± 1 Ma and 138 ± 3 Ma, respectively. Considering the Usugli Depression structural position as an upper fault slice of the Elikan metamorphic core, the obtained dates allow the formation of the mentioned core and, accordingly, the collapse of central part of the Mongol–Okhotsk orogeny to have occurred not prior to 140 Ma.

New U–Pb zircon (TIMS) results allow dating of protoliths of tonalite–trondhjemite orthogneisses of the Olekma Complex in the central part of the Chara–Olekma Geoblock (Aldan Shield) to 2825 ± 3 Ma and 2994 ± 3 Ma. Together with the results of previous geochronological studies, this proves that the Olekma Complex comprises heterochronous igneous rocks intensively reworked under amphibolite facies conditions and formed during different stages of geological evolution of the Aldan Shield.

Four metamorphic events were identified in the Early Precambrian history of the Eastern Sarmatia. The oldest Mesoarchaean (?) ultrahigh temperature (UHT) metamorphism at 900–1000 °C and 10–12 kbar occurred in the Kursk and Azov domains. Although attempts to constrain accurately the age of metamorphism failed, they provided evidence for the existence of the early Mesoarchaean ultra-hot orogen in the central part of the Archaean core of the Eastern Sarmatia. The 2.82 Ga metamorphism, widespread within the Eastern Sarmatia, finished the formation of the ancient Mesoarchaean basement. The granulite facies metamorphism at ∼750 °C and ∼5 kbar is confined to zones composed of gneisses and migmatites, while the epidote–amphibolite and amphibolite facies metamorphism occurred within preserved fragments of greenstone belts. The Palaeoproterozoic low-pressure metamorphism occured at 2.07 Ga in all Palaeoproterozoic structures under P-T conditions ranging from 350 °C at 2 kbar to 750 °C at 5 kbar. The metamorphic event was caused by a collision between the Volga-Uralia segment and Sarmatia at ca. 2.1 Ga. The youngest high-T granulite metamorphism at 850 °C and 5.5 kbar (2.04 Ga) recorded in the Bryansk domain likely reflects a thermal effect related to magmatic event that preceeded the main episode of the Osnitsk-Mikashevichi volcano-plutonic belt formation at the active margin of Sarmatia at 1.96–2.00 Ga.

U–Pb geochronological studies of garnet of the andradite–morimotoite series and Sm–Nd geochronological studies of this garnet and apatite from the Chikskii Massif (Tuva-Mongolia microcontinent) were carried out. The garnet studied is characterized by relatively high concentrations of U (14–16 ppm) and by a low level of common Pb (Pbс/Pbt = 0.07–0.1). The concordia age of garnet is 492 ± 2 Ma (MSWD = 0.01, probability 92%) and matches within the error with the Sm–Nd age determined by the isochrone for apatite, garnet, and bulk rock (489 ± 9 Ma, MSWD = 0.86). This allows us to consider calcic garnets of the andradite–morimotoite series as promising mineral geochronometers for U–Pb dating of ultrabasic alkaline rocks.

This paper reports on geochronological U–Pb studies of baddeleyite from nepheline syenite of the Korgere-Daba alkaline massif, which is the largest massif within the Sangilen Highlands (Tyva). The established age of rocks, 295 ± 1 Ma, indicates that, in the Early Permian, undersaturation by silica magmatism occurred in the region in addition to the alkaline-granite magmatism (Ulug-Tanzek, etc.). This age furthermore points to the need to make corrections in the conceptions of a petrophysical type for the Devonian Sangilen complex, which is traditionally distinguished in this region. Until now, the Korgere-Daba massif has been considered in this regard.

The formation stages of high-grade metamorphic complexes and the related granitoids of the Dzabkhan terrane basement are considered. The age data (U–Pb method, TIMS) of zircons from the trondhjemite block of the eastern part of the Dzabkhan terrane, which is directly overlain by the dolomite sequence of the Tsagaan Oloom Formation, are given. Trondhjemites yield the U–Pb zircon age of 862 ± 3 Ma. In their structural position, they are assigned to typical postmetamorphic formations that determine the formation and cratonization of rocks of the host block. The geochronological study of trondhjemites gives grounds to distinguish fragments of the continental crust in the Dzabkhan terrane basement, the formation of which occurred at different periods of time: ∼860 and ∼790 Ma. Geological–geochronological and Sm‒Nd isotope–geochemical studies indicate that the Dzabkhan terrane basement is not a single block of the Early Precambrian continental crust, but a composite terrane, comprising Neoproterozoic ensialic and island-arc structural and compositional complexes. Correlation of Sr isotopic characteristics with the 87Sr/86Sr variation curve in the Neoproterozoic and Cambrian seawater shows that carbonate deposits accumulated at the eastern margin of the Dzabkhan terrane near the end of the Neoproterozoic, 700–550 Ma, and in the central part of the terrane in the Early Cambrian, 540–530 Ma.

The crystallization age of Zhaunkar granites (829 ± 10 Ma) was determined by U–Pb zircon dating. Taking into account the data obtained earlier on the granite age (791 ± 7 Ma) in the Aktas Complex and the syenite age (673 ± 2 Ma) in the Karsakpai Complex, the Ulutau sialic massif is assumed to be composed of three igneous complexes formed during the Tonian–Cryogenian periods of the Neoproterozoic.

This paper reports new geological, geochronological (U-Pb method) and Sm-Nd isotope-geochemical data on the metamorphic and magmatic complexes of the South Hangay metamorphic belt located in the southern part of the Hangay group of the Precambrian blocks, along the junction zone between the Baidarik block and the Vendian-Late Riphean ophiolite complex of the Bayanhongor zone. A lower age limit of the early metamorphic episode of the disthene-sillimanite facies series (M2) is provided by the age of 603 ± 3 Ma obtained for gabbroids of the island arc association distinguished in the Tatsaingol complex. An upper age limit is determined by granites with ages of 562 ± 2, 564 ± 5, and 571 ± 9 Ma. Later superimposed metamorphism of the andalusite-sillimanite facies series (M2) was established in the southeastern part of the belt. The lower boundary of this metamorphism is constrained by the emplacement of quartz diorites at 552 ± 2 Ma, while the upper boundary is marked by postkinematic granites of the Tatsaingol pluton with an age of 545 ± 5 Ma. The protoliths of high grade metamorphic rocks contained Early and Late Precambrian rocks. The former could belong to the basement of the Baidarik block and/or its shelf, while the latter, to the rocks of the oceanic and island-arc complexes of the Bayanhongor paleobasin. Virtually, the continental crust, fragments of which are represented in the Tatsaingol complex, was formed within an interval around 610-560 Ma. The final stages in the formation of the South Hangay metamorphic belt coincided with the initiation of the Vendian-Early Paleozoic paleoocenic basins, volcanic islands, and island arcs in the Early Caledonian framing of the Precambrian Hangay block structure in the Late Vendian. By the time of amalgamation of structures of the Early Caledonian superterrane of Central Asia in the Late Cambrian-Early Ordovician (500-470 Ma), an “agglomerate” of the Precambrian Hangay blocks has been already formed.

U-Pb zircon isotopic data on rocks from the Kandalaksha-Umba zone of the Lapland granulite belt in the Por’ya Bay area constrain the age of the protolith of the apodacite (apotonalite) Opx-Bt granulite gneisses at 2799 ± 4 Ma, and the age of the apogabbronorite Grt-Opx-Cpx-Hbl crystalline schists at 2315 ± 23 Ma. The U-Pb sphene age of the magmatic crystallization of the postmetamorphic granodiorites is 1901 ± 5 Ma. The zircon yields the U-Pb age of the contamination of xenogenic zircons, which were captured during the dissolution of xenoliths of the host Grt-Opx-Cpx-Hbl crystalline schists in granodiorite melt. The comparison of the most important attributes of the endogenic histories of the adjacent Lapland Granulite and Belomorian Mobile belts testifies to their similar evolutionary histories: (1) the protolith age of the acid Opx-Bt granulites of the Lapland Belt (2799 ± 4 Ma) coincides with the protolith age of acid gneisses in the Belomorian Belt (2890-2690 Ma); (2) the ages of the gabbronorite protolith of Grt-Opx-Cpx-Hbl granulites in the Lapland Belt (2315 ± 23 Ma) and gabbro-anorthosite in the Kolvitsa Massif (2462-2423 Ma) are close to the protolith age of eclogitized gabbronorites in the Belomorian coronite suite (2.46–2.36 Ga); (3) the age of granulite metamorphism of acid and mafic rocks in the Lapland Belt is 1912–1925 Ma, and the age of eclogite metamorphism of gneisses and metabasites in the Belomorian Belt is approximately 1.9 Ga, i.e., their metamorphism took place in Svecofennian time; (4) the peak pressure of granulite metamorphism in the Lapland Belt was 9–11 kbar at a temperature of 800–850°C, whereas the peak metamorphic parameters of eclogite metamorphism in the Belomorian Belt were 10–12 kbar and 640–700°C. This means that the metamorphic complexes of the Lapland and Belomorian belts had the same Mezo- and Neoarchean protoliths hosting bodies of Paleoproterozoic gabbroids and were completely formed largely by a single cycle of Svecofennian high-pressure zonal metamorphism within a temperature range from the lowest grade of the eclogite to the granulite facies.

The Early Caledonian folded area of Central Asia comprises a variety of continental crust fragments with Early to Late Precambrian crystalline basement. Crystalline rocks, which form part of the Songino block, outcrop at the junction between the Dzabkhan and Tuva-Mongolian terranes. The Bayannur zone in the southern part of the Songino block contains the Bayannur migmatite-gneiss and Kholbonur terrigenous-metavolcanic metamorphic complexes. Previous studies provide the 802 ± 6 Ma age for the regional metamorphism and folding within the Bayannur complex. On the basis of the minimum Nd model age of 1.5 Ga, gneisses from this complex cannot be regarded as Early Precambrian. Two main rock associations were distinguished in the Kholbonur complex. Mafic metavolcanics compose the dominant lithology of the first rock association, whereas the second association comprises terrigenous-volcanic and predominantly terrigenous suites. The rocks of the predominantly terrigenous suite, including mudstones, sandstones, and conglomerates, are interpreted to derive from the Late Riphean accretionary prism. The lithology and composition of metaterrigenous rocks suggest that they were possibly derived from erosion of a volcanic arc. The upper age limit of this suite is constrained by postkinematic granites (790 ± 3 Ma; U-Pb zircon), the lower age is given by plagiogranite (874 ± 3 Ma; U-Pb zircon) from comglomerate pebbles. Therefore, the timing of deposition of this terrigenous suite can be bracketed by the 874–790 Ma time interval. These ages and compositional features of the Kholbonur complex terrigenous rocks suggest that the convergence took place at around 870–880 Ma and thus it can be correlated with the divergent processes between the blocks of continental crust composing the supercontinent Rodinia.

The basement of the south Ulutau sialitic massif, which is located in the western part of Central Kazakhstan, comprises metamorphized volcanogenic-sedimentary and plutonic complexes of Proterozoic age. The upper boundary of the metamorphism age corresponds to the age of nonmetamorphized syenites from the Karsakpai massif (673 ± 2 Ma, Late Riphean). U-Pb geochronological studies of accessory zircon were made, and a Late Riphean age of biotite alkali granite from the Aktas massif (the youngst metamorphic Precambrian igneous units in South Ulutau) was found. The obtained age estimate of 791 ± 7 Ma can be considered as the lower age limit of metamorphism. Thus, the last stage of regional metamorphism in South Ulutau took place in the second half of the Late Riphean, in the time interval of 790–670 Ma.

According to the results of U-Pb geochronological investigations, the age of the amphibolite protoliths (metabasalts) in the Ust’-Gilyui sequence within the Stanovoi Complex of the Amazar-Gilyui structural and formational zone in the Selenga-Stanovoi Superterrain of the Central Asian fold belt can be estimated at 193 ± 1 Ma. The Nd model age of the Ust’-Gilyui metasedimentary rocks is in the interval of tNd(DM) = 1.1–3.1 Ga. This information along with the previously obtained geochronological data are indicative of the fact that the Ust’-Gilyui sequence consists of metasedimentary and metavolcanic rocks of various ages: (1) volcanic rocks with the age of 193 ± 1 Ma; (2) metasedimentary and metavolcanic rocks broken through by the Paleozoic granitoids dated to 370 Ma and characterized by minimum estimations of tNd(DM) = 1.1 Ga, i.e., rocks with an age of 1.1–0.4 Ga. In addition, it is quite possible that this sequence also includes more ancient rocks. The SSS Amazar-Gilyui structural and formational zone is likely to be a tectonic melange composed of the metasedimentary and metavolcanic rocks of the Mesozoic and, probably, Paleozoic and Early Precambrian ages. The studied zone was formed in the Mesozoic, most likely, in the course of the collision processes initiated by the closing up of the Mongol-Okhotsk Ocean.

In this paper, we report U-Pb geochronological, Sm-Nd isotopic, and geochemical data for the basic schists of the Bryanta sequence of the Stanovoi complex of the Dzhugdzhur-Stanovoi superterrane of the Central Asian fold belt. It was shown that the protolith of the schists was composed of island-arc subalkali basalts, which crystallized at 1933 ± 4 Ma; the age of the earliest metamorphic processes is approximately 1890–1910 Ma. This metamorphic event could be related to the collision of the Aldan and Stanovoi continental plates or accretion-collision processes at the boundary of the Ilikan and Kupurin lithotectonic zones during the formation of the latter.

This paper describes the results of geochronological studies (U-Pb method over micro lots and single grains of zircon) of autochtonous and allochtonous granitoids of the Barguzinskii complex of the Angara-Vitim batolite of the petrotypical area in the basin of the Dzhirga and Kovyli rivers (tributaries of the Barguzin River). The age of crystallization of gneissose granitoids is 297 ± 5 Ma, and that of intrusive leucocratic biotite granites is 291 ± 1 Ma. The estimates of the age finalize the discussion on the age of granitoids of the Barguzin complex and cannot be considered as “rejuvenated.” The analyses of the geochronological data that have been obtained up to the present for granitoids of the Angara-Vitim batolite with the SHRIMP and U-Pb methods for large samples of zircons show that in the majority of cases they cannot be used for precise estimation of the age of their crystallization. The geochronological data obtained with use of the U-Pb method over micro samples and single grains of zircon allow one to make a conclusion on the formation of granitoids of the described complexes of the Angara-Vitim batholite that occurred within 303 ± 7–281 ± 1 Ma. Thus, the time length of formation of the largest in the eastern segment of the Central Asian belt of the Angara-Vitim batholite is not more than 22 Ma (minimum 6 Ma), which allows us to consider it as a large granitic province and is a boundary condition for development of the geodynamic models of its formation.

According to the results of U-Pb geochronological investigations, the hornblende subalkali diorite rocks making up the Tok-Algoma Complex in the eastern part of the Selenga-Stanovoi Superterrain of the Central Asian fold belt were formed in the Middle Jurassic rather than in the Middle Archean as was suggested previously. Thus, the age of the regional amphibolite facies metamorphism manifested itself in the Ust’-Gilyui rock sequence of the Stanovoi Complex and that superimposed on granitoids of the Tok-Algoma Complex is Mesozoic rather than Early Precambrian. The geochemical features of the Tok-Algoma granitoids are indicative of the fact that they were formed in the geodynamic setting of the active continental margin or a mature island arc. Hence, it is possible to suggest that the subduction processes along the southern boundary between the Selenga-Stanovoi Superterrain and the Mongolian-Okhotsk ocean basin in the Middle Jurassic resulted in the formation of a magmatic belt of over 500 km in length.

The Ulutau massif is located in the western part of Central Kazakhstan and is one of largest Precambrian sialic massif of this region. Geologically, the southern part of the massif is composed of volcanogenic and volcanogenic–sedimentary rocks of acid and rare basic composition metamorphosed under the green schist metamorphism facies. The northern and eastern parts of the massif are composed mainly of amphibolite facies metamorphic rocks, represented by amphibolites, gneisses, and amphibole crystalline schists (Fig. 1a).

This paper considers the geological structure, composition, and age of the Darkhintui, Barun-Gol, and Khuldat granitoid plutons of the Dzhida zone of Caledonides of the Central Asian Fold belts. These plutons were formed in the Late Cambrian-Early Ordovician in the range between 490 ± 2 and 477 ± 6 Ma, after tectonic juxtaposition of the oceanic and island-arc complexes of the Dzhida Zone and volcanogenic-carbonate-terrigenous rocks of the Khamardaban zone, i.e., at the collisional stage of the region evolution. Geological, geochronological, geochemical, and Nd isotope data indicate that the collisional granitoids of the Dzhida zone were derived by melting of continental crust thickened through accretion. The sources for parental melts of the granitoids were presumably Vendian-Early Cambrian juvenile igneous rocks of ophiolite and island-arc complexes, as well as the crustal material of the Lower Paleozoic flyschoid sediments of the back-arc basin of the Dzhida zone and metaterrigenous rocks of the Khamardaban zone.

The U-Pb age of the manganotantalite from rare-metal pegmatites of the Vishnyakovskoe deposit (East Sayan Belt) has been assessed at 1838 ± 3 Ma. The acquired data indicate the pegmatites of this deposit and associated granites of the Sayan complex belong to the postcollision South Siberian igneous belt (1.88–1.84 Ga), which stretches along the southwestern frame of the Siberian Craton by more than 2500 km, from the Yenisei Ridge to the Aldan Shield. Formation of this igneous belt is related to joining (starting from about 1.9 Ga BP) of the series of continental microplates and island arcs to the Siberian Craton; this led to final stabilization of the craton at about 1.8 Ga BP.

In the structure of west Kyrgyz Ridge (North Tien Shan), a great role is played by complexly dis� located Upper Precambrian-Cambrian terrigenouscarbona te and shale strata, as well as by granitoids that comprise several coupled WNWstriking synforms and anti forms, the largest of which is the Makbal antiform. Southeast of the core of this antiform, granitoids comprise the large Kara Dzhilga massif and several massifs that are of lesser size and have tectonic correlations with the hosting terrigenouscarbonate strata. In the Kara Dzhilga massif, the rocks of three penetration phases are distinguished; contacts between rocks are often of tectonic character. The early phase is presented by monzonite and monzodiorite; the main one, by largepor� phyric biotitic granites; and the additional one, by aplitic granites and pegmatites. By the chemical compo� sition, granites of Kara Dzhilga massif of the main phase correspond to subalkaline granites of highpotas� sium calcalkali series. The age of their crysta llization (zirconbased U-Pb method) is 1131 ± 4 Ma (Ste� nian). The formation of Stenian granitoids in the North Tien Shan may be related to development of Grenville fold belts, whose fragments were identified in the units of the Central Asian Belt. Tectonic correla� tions between these granitoids and hosting terrigenouscarbonate strata appeared as a result of immersion to significant depths and subsequent exhumation into the upper crustal horizons in the Early Ordovician.

The volcanogenic Kuuspek Formation is a well-defined part of the succession of the Pre-Vendian complexes of the Kokchetav massif (Northern Kazakhstan). The formation is built up of mildly metamorphosed acid lavas, tuffs, and tuffaceous sandstones. At the reference site to the west of the Kokchetav Mountains, the rocks of the Kuuspek Formation compose hinges of small anticlinal folds with sericite-quartz schists of the Late Riphean Sharyk Formation forming the limbs. The Kuuspek Formation lavas are high-alumina rhyolites of high-potassium calc-alkaline series. The U-Pb zircon age of the rhyolites is 1136 ± 4 Ma, thus referring to the Middle Riphean. The Kuuspek rhyolites form the basal part of the Precambrian sedimentary cover of the Kokchetav massif. The cover also comprises schists, limestones, and dolomites of the Sharyk Formation, and quartzites and quartzitic schists of the Late Riphean Kokchetav Formation.

The Hercynian mobile belts in Central Asia comprise the Hercynian proper and the Late Hercynian (Indosinian) belts separated by the South Gobi microcontinent, the origin of which is related to the evolution of the South Mongolian and Inner Mongolian basins with the oceanic crust. Crystalline complexes within these belts occur as tectonic sheets of a variety of sizes. At the early stages, the metamorphic grade of these complexes reached conditions of high-temperature subfacies of amphibolite and locally developed granulite facies. In tectonic terms, the Hercynian belt of metamorphic rocks is situated at the margin of the North Asian Caledonian continent and extends from the southeast to the northwest along the southern slope of the Gobi, Mongolian, and Chinese Altai to East Kazakhstan, where metamorphic rocks are localized in the Irtysh Shear Zone. All these rocks are combined into the South Altai metamorphic belt of more than 1500 km in extent. Another belt of isolated outcrops of crystalline rocks conventionally combined into the Indosinian South Gobi metamorphic belt is traced along the junction of the Hercynides with the South Gobi microcontinent. The high-grade metamorphic rocks within both belts are not fragments of an ensialic Caledonian or older basement. These rocks were formed 390–360 and 230–220 Ma ago as a result of the closure of the Tethian South Mongolian and Inner Mongolian oceanic basins (Paleotethys I and Paleotethys II). The spatial position of the South Altai and South Gobi metamorphic belts is caused by the asymmetric structure of the Tethian basins, where active continental margins are expressed most distinctly along their northern parts, while passive margins extend along the southern parts (in present-day coordinates).

The Chupa nappe of the Belomorian Complex contains aluminous silica-undersaturated rocks with corundum, which are characterized by extremely low 18O/16O (whole-rock δ18O up to −21‰). Revealed isotopic anomalies are explained by the influence of meteoric waters that were modified through evaporation-precipitation cycles (Rayleigh distillation) under cold climatic conditions. In order to estimate whether the decrease in δ18O occurred prior to metamorphism of the protoliths of the Chupa Sequence or during water percolation in the course of metamorphic or postmetamorphic transformations, we studied oxygen composition in the rocks and minerals and conducted U-Pb dating on single zircons from corundumbearing rocks of Khitostrov. U-Pb zircon dating allowed us to distinguish the following stages: (1) formation of protoliths of the corundum-bearing rocks and protoliths of the Chupa Sequence 2.9–2.8 Ga ago; (2) metamorphism under the amphibolite-facies conditions 2747 ± 6 Ma ago; (3) metamorphism under the amphibolite and greenschistfacies conditions 1.83 Ga ago. Oxygen isotopic anomalies were presumably formed at the pre-metamorphic stage and were not related to the Svecofennian metasomatism, as was suggested previously (Serebryakov et al., 2007). The possible protoliths for the corundum-bearing rocks could be Archean allochthonous complexes, whose composition, including silica deficiency and high alumina content, was determined by weathering. Meteoric fluid sharply depleted in 18O could be entrapped and buried with fragments of the weathering crust, and later, together with the protoliths of the Chupa gneisses, was involved into collisional processes and subjected to high-grade metamorphism at 2750–2720 Ma.

According to U–Pb dating, the granitoids of the Tyrma–Bureya complex in the northern Bureya–Jiamusi superterrane of the Central Asian fold belt are not of Paleozoic, as previously thought, but of Mesozoic age (Nizhnyaya Stoiba massif, 218 ± 2 Ma; Talakan and Ust’-Dikan massifs, 185 ± 1 Ma). They formed at the early stages of collision between the North Asian and Sino-Korean cratons and the intervening Amur superterrane.

The sequence of rock and ore formation at the Yermakovsky beryllium deposit is established on the basis of geological relationships and Rb-Sr and U-Pb isotopic dating. The Rb-Sr age of amphibolitefacies regional metamorphism is determined for quartz-biotite-plagioclase schist (266 ± 18 Ma) and dolomitized limestone (271 ± 12 Ma) of the Zun-Morino Formation. The U-Pb zircon age of premineral gabbro is 332 ± 1 Ma. The Rb-Sr age of gabbro is somewhat younger (316 ± 8.3 Ma), probably owing to the effect of Hercynian metamorphism on sedimentary rocks of the Zun-Morino Formation and gabbroic intrusion that cuts through it. The U-Pb zircon age of gneissose granite of the Tsagan Complex at the Yermakovsky deposit is 316 ± 2 Ma, i.e., close to the age of metamorphism superimposed on gabbro rocks. The U-Pb zircon age of preore granitic dikes, estimated at 325 ± 3 and 333 ± 10 Ma, is close to the age of gabbro. The Ar/Ar age of amphibole from a granitic dike (302.5 ± 0.9 Ma) probably displays a later closure of this isotopic system or the effect of superimposed processes. The Rb-Sr age of alkali syenite intrusion is 227 ± 1.9 Ma. The U-Pb zircon age of alkali leucogranite stock pertaining to the Lesser Kunalei Complex is 226 ± 1 Ma, while the Rb-Sr age of beryllium ore is 225.9 ± 1.2 Ma. These data indicate that beryllium ore mineralization is closely related in space and time to igneous rocks of the Lesser Kunalei Complex dated at 224 ± 5 Ma and varying from gabbro to alkali granite in composition. Thus, the preore Hercynian magmatism at the Yermakovsky deposit took place ∼330 Ma ago and was completed by metamorphism dated at 271–266 Ma. The ore-forming magmatism and beryllium ore mineralization are dated at 224 ± 5 Ma. Postore magmatic activity is scarce and probably correlated with tectonic melange of host rocks.

95 Raremetal magmatism covering the age range of more than 1 billion years, from the Late Riphean to the Triassic, is widely abundant within the southern margin of the Siberian Platform and its folded sur� rounding. Late Riphean massifs of alkali-ultrabasic rocks with carbonatite of the Beloziminsk Complex, Ordovician-Triassic massifs of alkali granite (Arys� kan, Zashikhin, Ermakov, and others), as well as numerous massifs of lithium-fluorine granite includ� ing the spodumene variety, are related to the most wellknown manifestations of raremetal magmatism, which control the formation of large deposits of rare metals, rare elements, and rare earth elements. Until recently, the ideas about their age were based mainly on geological data. Only in the last few years have geo� chronological investigations, which allowed us to esti� mate the age and tectonic conditions of related mag� matic processes in geological evolution of the southern surroundings of the Siberian Platform, been carried out (1). However, the regularities of raremetal mag� matism in the structures of this region are not under� stood completely for some epochs. In particular, this relates to the epoch when the unique complex rare� metal-rareearth deposit UlugTanzek (Eastern Tyva) was formed. The existing estimations of age for host alkaline granitoids vary within very broad limits (229- 217 Ma, K-Ar method by potassic feldspar) and cover the whole Triassic (2). However, this age range in the region is amagmatic as a whole. Because of this, the reliability of age estimations obtained is doubtful and, therefore, there is a question about the geological events that controlled the formation of the deposit. In this paper we present the results of dating of alkaline granitoids of the UlugTanzek Massif by the U-Pb method for zircon and the Ar-Ar method. With account for the geochronological data obtained, we analyzed its position in the structure of magmatic areals of the same age and, on this basis, reconstructed the geodynamic environment of raremetal magma� tism in the corresponding epoch. The UlugTanzek Massif of alkaline granitoids is located in southeastern Tyva within the Sangilen part of the Tyva-Mongol microcontinent, where it intrudes metamorphosed Vendian-Cambrian terrige� nous-carbonate deposits of the Kaakhem structural- facial zone. The massif is composed of quartz-albite- microcline granite with complex (Ta, Nb, Zr, Hf, REE, Li, Th, U, and cryolite) ore.

U-Pb geochronological results confirm the Mesozoic age (124 ± 1 Ma) of the Beket granitoid complex, previously interpreted as being one of the markers amongst the Early Proterozoic magmatic complexes within the Amur superterrane (microcontinent) of the Central Asian Fold Belt. This implies that the structural and metamorphic amphibolite facies overprints documented either in the Beket granitoids or Gonzha host rocks are evidently Mesozoic rather than Early Proterozoic in age.

Charnockite intrusions of the Tatarnik Complex located in the Davan shear zone are the youngest man� ifestations of granitoid magmatism in the northwest� ern part of the Baikal region [1]. The shear zone has a submeridional zone of dislocations separating the Chuya salient composed of Early Precambrian high� grade metamorphic rocks and granitoids and the North Baikal volcano–plutonic belt comprised of Early Proterozoic (1.88–1.85 Ga) volanogenic–sedi� mentary rocks of the Akitkan Group and granitoids of the Irel Complex. Earlier Paleoproterozoic metamor� phic rocks of the Sarma Group are located to the south of this belt. It is necessary to mention that the latest events of Early Proterozoic magmatism within the considered region, such as volcanic rocks of the North Baikal belt, granitoids of the Chuya–Kodar, Kodar, Sayan, and Tarak Complexes, as well as rapakivi of the Primorsk and charnockite of the Shumikhin Com� plexes, are related to the formation of the postcolli� sional Southern Siberian magmatic belt (1.88– 1.84 Ga) extending for a distance of >2500 km along the southwestern boundary of the Siberian Platform from the Yenisei Ridge to the Aldan Shield [2]. Charnockite of the Tatarnik Complex usually forms relatively small intrusive bodies located in the Davan zone and cuts blastomilonites of this zone, as well as rocks of the Sarma and Akitkan Groups (Fig. 1). As a rule, they have a massive texture. Only sometimes is trachytic texture observed in endocontact zones. The chemical composition of charnockite relates to quartz

Carbonatites associated with syenites and subalkalic mafic rocks (lamprophyres) occur in the Himalayan continental collision zone, and this suggests their possible existence in other Phanerozoic collisional settings. The Early Paleozoic Ol’khon collisional system in Western Cisbaikalia is considered one of the possible occurrences. Subalkalic gabbroids as well as peculiar carbonate (brucite marbles) and calc-silicate rocks were found here, within the Tazheran massif of alkalic and nepheline syenites. Alkalic syenites, nepheline syenites, and calciphyres were dated at 471 Ma, 451–464 Ma, and 466 Ma, respectively, and their ages correspond to the main collisional events in the system. A geochemical description of igneous and carbonate rocks in the massif is provided. Close mapping showed unusual syenite and brucite marble combinations and the frequent vein or pipe-like form of carbonates and calciphyres corresponding to their magmatic intrusion. But carbonatite nature of the marble mentioned above does not fit their typical crustal geochemical features. Not ruling out the possibility of total change of geochemical signatures of mantle carbonatite in the collisional medium, we offer two other possible explanations for these facts: (1) melting of carbonate masses by syenite and mafic magmas, followed by carbonate melt intrusion into the upper crust, and (2) protrusion of carbonates into syenites and gabbroids at the late stages of the contact action of a silicate magma. In this case the above-mentioned carbonate structural features result from late recrystallization, whose mechanism is yet to be explained.

Large anorthosite massifs (or autonomous anorthosites) are typical magmatic complexes of Early Precambrian structures. They are usually formed at the postorogenic stages of their evolution and serve as indicators of their intraplate activation. These massifs remain enigmatic from the petrological point of view, but provide important information on the geology and evolution of host structures. Anorthosite massifs were found in Mongolia in the second half of the 20th century. These are the small Mustulin and Khodzhulingol massifs in the Tarbagatai block, and Olonkhuduk Massif in the Dzabkhan microcontinent (Fig. 1). One more large anorthosite massif was recently found by us in the northern part of the Tarbagatai block, in the lower reaches of the

The ophiolite complexes outcrop extending more than 700 km in the Dzhalair-Nayman zone located between the Chuya-Kendyk Tas (in the southwest) and Aktau-Dzhungar (in the northeast) Precambrian sialic massifs in South Kazakhstan. The most complete ophiolite sections are described in the central (Andassai massif) and southeastern (Dulankara massif) parts of the zone. Plagiogranites occur in a sheeted dyke complex in the upper part of ophiolite sections. A bimodal volcanic series occurs atop the section. The U/Pb zircons ages for the Andassai and Dulankara plagiogranites are 519 ± 4 and 521 ± 2 Ma, respectively. Ophiolites associated with bimodal volcanic series are also found in the north and northeast of Kazakhstan. They may form, together with the Lower Cambrian complexes of the Dzhalair-Nayman zone, a single paleostructure, whose fragments are well-traceable for over 2000 km

Granitoids and metamorphic rocks of the Baidarik basement block of the Dzabkhan microcontinent are studied in terms of geology, geochronology (U-Pb dating of zircon microfractions and individual grains) and Nd isotopic-geochemical systematics. As is established, the formation history of metamorphic belt (disthene-sillimanite facies) in junction zone of the Baidarik block and Bayankhongor zone of the Late Riphean (∼665 Ma) ophiolite association characterizes development of the Vendian (∼560–570 Ma) active continental margin. The high-P metamorphic rocks of that time span evidence formation of structures with the Earth’s crust of considerable thickness. In Central Asia, events of the Vendian low-gradient metamorphism are established also in the Tuva-Mongolian massif, Kan block of the East Sayan Mountains, and South Chuya inlier of the Caledonides in the Altai Mountains. Based on these data, it is possible to distinguish the Late Baikalian stage in development of the Early Caledonian superterrane of Central Asia, which antedated the subsequent evolution of this structure during the Late Cambrian-Ordovician. The high-gradient metamorphism that affected most intensively the southeastern part of the Baidarik block can be correlated with the Early Paleozoic (525–540 Ma) evolution of active continental margin and associated development of the Vendian oceanic basins and island arcs of the Ozernaya zone.