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The principal possibility of using high-uranium metamict zircon with a high self-irradiation α-dose for U–Pb geochronological studies (ID-TIMS) is demonstrated. The application of the optimal parameters of “chemical abrasion,” accompanied by preliminary high-temperature annealing, allowed us to estimate the age of Li–F granites of the Turga massif (Eastern Transbaikalia) (146 ± 4 Ma and 141 ± 1 Ma).

The paper reports geochemical, geochronological (ID–TIMS zircon U–Pb) and isotope–geochemical (Nd, Pb) study of granitoids of the Kodar complex developed in the western part of the Aldan shield. It has been established that these rocks can be classified as postcollisional A–type rapakivi granites, which together with the mafic–ultramafic rocks of the Chinei complex compose a single magmatic association formed within 1876 ± 4–1859 ± 2 Ma. The massifs of this association are a part of the giant South Siberian magmatic belt over 2500 km in length, which was formed at the final stage (1.88–1.84 Ga) of evolution of the Paleoproterozoic orogen. Globally, this belt is the largest stitching suture, which marks the formation of the Siberian craton and its entrance into the Paleoproterozoic Nuna supercontinent. The formation of the initial magmas of the Kodar granitoids was related to the mantle–crustal interaction during the mixing of primary mafic mantle magmas or their derivatives with anatectic melts derived through partial melting of the Archean lower continental crust of the region under the thermal influence of mafic magma. The crustal component in the source clearly predominates and has a heterogeneous nature. The mantle component is mainly represented by ancient enriched mantle, with the possible contribution of the OIB–type component.

The results of geological, geochemical, Sm–Nd isotopic geochemical studies of metamorphic rocks of the Djagdagle Formation and U–Pb geochronological studies of its zircons are presented. In correlation schemes of geological complexes of the Bureya Terrane, this formation is the oldest (conditionally, Late Archean) amid other formations of the terrane; thus, it is considered its basement. The biotite and two-mica garnet-bearing gneisses of the formation formed owing to transformation of primary sedimentary rocks. The maxima on the relative probability curve of zircon age correspond to 487, 541, 690, 778, and 896 Ma. Thus, the Djagdagle Formation is Paleozoic rather than Early Precambrian, as was considered before. The lower age boundary of the accumulation of the protolith is identified by the age of the youngest zircon population of ~487 Ma. Similar ages of some cores and rims of zircons indicate that the rocks of the protolith underwent structural metamorphic transformations under PT conditions of amphibolite facies. The results of Sm–Nd and Lu–Hf isotopic studies indicate that the geological complexes which originated by means of reworking of the Mesoproterozoic crust could have been the source of primary sedimentary rocks. Taking into account the lack of Mesoproterozoic (and older) rocks in the structure of the Bureya Terrane, it can be suggested that the sources included some amount of ancient recycled material. Similar geological evolution of the Bureya and Jiamusi terranes is suggested on the basis of similar age ranges of metasedimentary rocks of the Djagdagle Formation and Turan Group of the Bureya Terrane and the Kimkan Formation of the Jiamusi Terrane. This is also evident from their synchronous Neoproterozoic magmatism.

The Mongol–Okhotsk Belt, a major structural element of East Asia, is probably the youngest orogenic segment within the Central Asian Orogenic Belt. However, the timing of final closure of the Mongol–Okhotsk Ocean remains unresolved. Here, we present detrital zircon U–Pb–Hf isotopic data and whole-rock geochemical data (major and trace elements and Sm-Nd isotopes) for the metasedimentary rocks from the Un'ya–Bom Terrane, Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane. Our new zircon U-Pb ages suggest that all sedimentary formations along the Dzhagdy Transect are early Mesozoic in age, rather than Paleozoic as previously thought. The detrital zircons from the metasedimentary rocks in the Un'ya–Bom Terrane, the Dzhagdy Terrane, and the eastern part of the Tukuringra Terrane yielded the youngest concordant ages of 194 ± 4, 193 ± 2, and 171 ± 2 Ma, respectively. Moreover, we note that the so-called sedimentary formations of these terranes are not single sedimentary sequences as previously suggested, but a set of an olistostrome or tectonic melanges composed of rocks of different ages and origins. These sedimentary formations are probably relics of the Mongol–Okhotsk remnant basin that formed in the “gaps” between the southern margin of the North Asian Craton and the Amur Block during their collision. The absence of detrital zircons younger than 171 Ma in the sedimentary rocks of the Mongol–Okhotsk basin implies that the final closure of this basin could have taken place at the boundary of the Early and Middle Jurassic as a result of the collision or the development of the Mongol–Okhotsk orogenic belt in this region. After that, the Mongol–Okhotsk Belt underwent intense deformation related to within-plate strike-slip faulting, which could be attributed to the late Mesozoic rotation of the North Asian Craton relative to the continental massifs of East Asia.

The Bureya Massif is located in the eastern segment of the Central Asian Orogenic Belt (CAOB) and its tectonic affinity and Precambrian evolution is highly controversial. Here we present mineralogical, whole-rock geochemical (major and trace elements and Sm–Nd isotopes) and zircon Hf isotopic data, together with zircon geochronological and mica 40Ar/39Ar dating of the biotite and amphibole gneisses from the Tulovchikha metamorphic complex (previously considered as Archean or Paleoproterozoic basement) in the Bureya Massif, in order to investigate their protolith, metamorphic and deformation ages, petrogenesis, and tectonic implications. LA-ICP-MS U–Pb dating of magmatic zircons from the biotite gneiss, the amphibole–biotite gneiss, and the amphibolite yields single zircon age populations cluster at ~950 Ma, ~920 Ma and ~940 Ma, respectively. The narrow zircon age ranges, together with the morphological features of the zircon crystals and the geochemical data, indicate that the studied metamorphic rocks have a magmatic origin and their protoliths were formed in the early Neoproterozoic (i.e., 950–920 Ma). The consistent formation ages further suggest that the Neoproterozoic gabbro–granitic rocks within the Nyatygran Complex in the Bureya Massif probably represent the protolith of the studied metamorphic rocks. The biotite and amphibole-biotite gneisses of the Tulovchikha metamorphic complex yield whole-rock Nd model ages (tNd(DM)) of 2.4–1.5 Ga and Hf zircon crustal model ages (tHf(C)) of 1.7–1.2 Ga, indicating that the precursors of the Tulovchikha Complex gneisses formed from the reworking of Meso–Paleoproterozoic rocks or mixed Neoproterozoic juvenile and Meso–Paleoproterozoic crustal sources. Considering that the Bureya and Jiamusi massifs experienced similar Neoproterozoic magmatic events, we suggest that these massifs form a contiguous crustal unit and share a common geological history. The rocks of Tulovchikha metamorphic complex in the studied area experienced epidote-amphibolite to amphibolite facies metamorphism probably in the early Paleozoic, as evidenced by the 471 ± 19 Ma age of a metamorphic zircon with a low Th/U ratio (

In this paper we present new detrital zircon U–Pb ages and Lu–Hf isotopic data as well as whole-rock geochemical data for siltstones of the Cambrian Chergilen and Allin formations in the Mel’gin Trough of the Bureya Massif, Russia. Our aim is to constrain the provenance and tectonic settings of these strata. The detrital zircons in these rocks are dominantly Neoproterozoic in age (∼80% of all zircons), along with some Mesoproterozoic and Paleoproterozoic zircons, and the main age peaks are at ca. 1.78, 1.64, 1.45, 1.18, 0.94, and 0.82 Ga. The zircon Hf and whole-rock Sm–Nd isotopic compositions, together with geochronological data, show that the main sources of the Cambrian sediments were Neoproterozoic and Mesoproterozoic igneous complexes formed by the reworking of Paleoproterozoic rocks. The main age populations of detrital zircons from the Cambrian siltstones in the Bureya Massif are similar to those of detrital zircons from the Neoproterozoic and early Paleozoic deposits within the Jiamusi Massif, suggesting that they share a common history. However, the crustal basements of the Bureya and Jiamusi massifs are different from those of other massifs in the eastern part of the CAOB, such as the Erguna, Khanka, Khingan, and Songnen–Zhangguangcai Range massifs. The wide Neoproterozoic magmatic events suggest that the Bureya and Jiamusi massifs have an affinity to the Tarim Craton or the northern Tian Shan block, different from the North Asian and North China cratons.

Palaeoproterozoic amphibole-biotite orthogneisses with a protolith age of ~ 1840 Ma and Neoproterozoic muscovite-chlorite orthogneisses with an estimated protolith age of ~ 790 Ma have been identified in the structure of the Zheltau terrane (Southern Kazakhstan; west Central Asian Orogenic belt). In addition, metasedimentary complexes represented by prevailing garnet-mica schists and subordinate muscovite-chlorite schists with obtained detrital zircon ages in the range of 604 - 2819 Ma (with two peaks at ~ 991 Ma and ~ 1082 Ma) also comprise the Zheltau terrane. In accordance with the Sm-Nd whole-rock isotopic compositions, the protolith of the observed Palaeoproterozoic orthogneisses formed as a result of a mixing of the Neoarchean crustal source with a juvenile source, whereas the formation of the Neoproterozoic orthogneisses protolith may have been related to the melting of Palaeoproterozoic crustal material. In turn, Late Mesoproterozoic – Early Neoproterozoic granitoids or felsic volcanic rocks, which formed as a result of the melting of Palaeoproterozoic continental crust, are considered as possible sources for the studied detrital zircons obtained from the schists. The terrigenous protolith of the schists from the Zheltau terrane accumulated in the range of ~ 600 to ~ 490 Ma, corresponding to the Ediacaran-Cambrian. Subduction processes in the Early Palaeozoic led to the burial of different horizons of the Zheltau terrane continental crust to significant depths; some of the complexes experienced high-pressure metamorphism at P 15 – 18 kbar; T 750 – 850 °C (high-pressure granulites), whereas most of the rocks were evidently metamorphosed at maximum amphibolite facies and avoided high-pressure re-equilibration. The spatial proximity of the studied metamagmatic and metasedimentary crustal complexes and similar metamorphic changes during the latest stages of retrogression imply their possible mutual exhumation from different levels during the period between 490 and 470 Ma and their following juxtaposition as a package of tectonic slices.

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.

Biotite plagiogranite intruding sediments of the Kodar Sub-Group of the Udokan Group that have both undergone amphibolite grade alterations has been dated by the U–Pb ID TIMS technique using zircon to 2105 ± 6 Ma. This age estimate to a first approximation corresponds to the younger age limit of deposition of the siliciclastics in the lower section of the Udokan Group.

For the first time, the U–Pb age is determined for detrital zircons of quartzite–schist sequences, which are part of the Precambrian basement of the Aktau–Mointy Block (Central Kazakhstan) along with Neoproterozoic felsic volcanic (925–920 Ma) and granitic (945–917 Ma) rocks [6]. We analyzed 219 zircon grains from small-grained quartzites of the northern part of the block (Mt. Bol’shoi Alabas) including 206 grains with concordant age (1149–1273, 1276–1975, 2354–2592 Ma). These ages indicate the Mesoproterozoic, Paleoproterozoic, and Neoarchean rocks as provenances. The youngest statistically significant age peak of 1209 Ma indicates that the quartzite–schist sequences accumulated 1200–900 Ma ago (at the end of the Mesoproterozoic and beginning of the Neoproterozoic) prior to the formation of the Early Neoproterozoic felsic rocks and granites.

The U–Pb (ID TIMS) geochronological studies of single zircon grains and their fragments have made it possible to establish that rare-metal alkaline granites of the Katugin massif (2055 ± 7‒2066 ± 6 Ma) underwent high-temperature transformations at age levels of ~1921 ± 5 and 1876 ± 7 Ma.

Geochronological (LA–ICP–MS) U–Th–Pb studies of detrital zircon of the Late Cenozoic sand deposits on Ol’khon Island have been performed. It has been shown that their main source is represented by Early Paleozoic igneous and metamorphic complexes of the Ol’khon Terrane of the Central-Asian Mobile belt and Late Carboniferous–Early Permian granitoids of the Angara–Vitim batholite. Sands from the source were transported over a distance of no less than 100 km. It is supposed that it was effectuated by strong air flows, over the ice on the Lake Baikal in particular.

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.

A migmatite–gneiss complex made up of paraand orthogneisses and crystalline schists with bodies of ultrametagenic tonalites is distinguished in the basement of the northwestern part of the Chuya–Kendyktas Massif. ID-TIMS dating of accessory zircon from orthogneisses and ultrametagenic tonalites in combination with LA-ICP-MS analyses of detrital zircons from garnet–biotite paragneisses showed that the migmatite–gneiss complex was formed after protoliths with an age within 800–770 Ma and completed its evolution in the first half of the Neoproterozoic.

Geological and geochronological U–Pb (zircon ID-TIMS) and 40Ar/39Ar (amphibole) data were obtained for six anorogenic magmatic associations in the Gobi Altai, southwestern Mongolia, in order to reveal its relationships with Late Paleozoic tectonothermal events in the southern part of the Central Asian Orogenic Belt (CAOB). In the Gobi Altai massifs of alkaline granites and grabens filled with bimodal volcanic suites occur as a chain 450 km long east–southeast direction. The massifs and volcanic fields are controlled by contacts of pre-Ediacaran continental crustal blocks with Late Neoproterozoic–Cambrian juvenile ophiolite and arc-type complexes of the Lake zone. Gobi Altai alkaline granites bear sodic-rich mafic silicate minerals and possess typical properties of ferroan A-type granites. Our geochronological data constrain emplacement time of the Gobi Altai alkaline granites and bimodal volcanic rocks at 293 ± 1–279 ± 1 Ma. This age interval coincides with timing of the emplacement of I-type granites (with a few S-type granites) and gabbroic intrusions in the Mongolian and Chinese Altai as well as with numerous massifs of A-type granites, layered mafic–ultramafic intrusions, and eruption of bimodal volcanic rocks between the southern edge of the Siberia craton and the northern margins of the Tarim and North China cratons. Hence, the Gobi Altai anorogenic magmatic complexes were produced by a large-scale Late Paleozoic magmatic event (or events) that encompassed a wide spectrum of terranes in CAOB. The most realistic models explaining these magmatic processes are: (i) the effect of the Tarim mantle plume, (ii) slab (or slabs) break-off after subduction blocking due to accretion of terranes of various types.

The U–Pb geochronological data on detrital zircons from placers confined to Neoproterozoic quartzite–schist sequences, which are widespread in the Kokchetav massif of northern Kazakhstan, are discussed. Detrital zircons (332 grains in total) originate from the ore occurrences in the central, northern, and western parts of the massif. The concordant ages of detrital zircons from all the examined occurrences largely correspond to intervals of 1017–1528, 1628–1946, and 2653–2739 Ma. The obtained data imply that material of quartzite–schist sequences of the Kokchetav massif was provided by Mesoproterozoic, Paleoproterozoic, and Neoarchean rock complexes. The lower age limit determined for these sequences is approximately 1.06 Ga. The dates obtained for detrital zircons are most consistent with events that took place in Laurentia. They correspond to the formation and breakup of the Columbia/Nuna supercontinent (approximately 1650–1580 and 1450–1380 Ma ago, respectively) and formation of the Rodinia supercontinent in the period of 1300–900 Ma ago.

Jabel Sayed, in the northern part of the Arabian Shield, is an alkaline granite complex. It consists of syenogranites and aegirine–riebeckite alkali feldspar granites intruded into an older granodiorite–tonalite suite. Elemental geochemistry attests that the syenogranite and the alkali feldspar granite represent a genetically related post-collisional A2-type granite intrusion (e.g., high K2O + Na2O, FeO∗/MgO, Ga/Al, and Y/Nb, and low CaO, Ba, and Sr). U–Pb zircon dating and Nd isotopes of the alkali feldspar granites indicate an age of 593 Ma, eNd(t) values of +4.9 to +5.3 (mean = +5.1), and depleted mantle model ages (tDM) between 0.78 and 0.88 Ga. These isotope results are in agreement with a juvenile magma source of Neoproterozoic age like that responsible for forming most other Arabian–Nubian Shield crust. The alkali feldspar granites have substantial modal content of albite and fluorite, wide variation of HFSE and REE and exhibit tetrad effects in REE patterns that indicate interaction with hydrothermal F-rich fluids. The fluids caused secondary metasomatic alteration superimposed on the granitic rocks. The result of the fluids–granitic rock interaction is a metasomatic pegmatite rim, which carries economic levels of HFS elements and REE, and a red granite variety (altered syenogranite) characterized by large variation in trace element abundances. Geochemical features in the granitic rocks such as strong linear positive correlation of Ta versus Nb and Zr versus Hf indicate magmatic origin of the fluids and emphasize that the behavior and enrichment of Ta and Nb are largely controlled by magmatic processes. Based on the geochemical and Nd isotopes compositions, we propose an origin for the Jabel Sayed granites which involved fractional crystallization of a parental magma derived by the partial melting of a crustal protolith accreted between 780 Ma and 880 Ma. This crustal protolith has juvenile geochemical and isotopic composition and was extracted from a subduction modified mantle source.

The U–Pb (zircon) age of 250 ± 1 Ma was determined for differentiated gabbro–monzonite intrusions, which were formed prior to metamorphism of high-temperature amphibolite facies of high pressures in the southeastern part of the Sutam block of the Stanovoi suture. These data indicate that this episode of metamorphism belongs to the Mesozoic stage of evolution of the Stanovoi suture rather than to the Early Precambrian, as was suggested before. It most likely corresponds to the age of the last episode of the high-temperature metamorphism of amphibolite facies (140 Ma), which is manifested within the Dzhugdzhur–Stanovoi superterrane of the Central Asian foldbelt adjacent from the south to the Stanovoi suture and is caused by collision of the Dzhugdzhur–Stanovoi superterrane and the epi-Paleozoic Amur microcontinent during the closure of the Mongol–Okhotsk oceanic basin.

Data obtained on the Khangai zonal magmatic areole in the Central Asian Orogenic Belt indicate that accessory zircons in alkaline granitoids have crystallogenetic characteristics that generally reflect specifics of the evolution of the parental alkaline magmas. The late differentiation of these magmas was characterized by an increase in the concentrations of trace and rare-earth elements, water, and fluorine in the residual melts and aqueous salt-bearing fluids. Their action was associated with local transformations of the zircon, first and foremost, with local enrichment of zircon crystals in fluid inclusions and in crystalline inclusions of sulfides an other ore minerals. This disturbed the Pb isotopic composition of the zircon, for example, led to its enrichment in common (admixture) Pb and thus caused significant errors and uncertainties in the U-Pb zircon dates. Our recently obtained data indicate that one of the most efficient methods of preparing accessory zircons enriched in common Pb to their U-Pb dating is their preparatory treatment with acids (Makeev, 1981; Mattinson, 1994, 1997, 2005). The application of this technique makes it possible to rid the zircons of phases enriched in common Pb and usually to obtain reliable geochronologic data. The method of preparatory acid treatment of zircons is thus best suitable for geochronologic studies of granitoids of elevated alkalinity.

The Burpala alkaline massif is a unique geological object. More than 50 Zr, Nb, Ti, Th, Be, and REE minerals have been identified in rare-metal syenite of this massif. Their contents often reach tens of percent, and concentrations of rare elements in rocks are as high as 3.6% REE, 4% Zr, 0.5% Y, 0.5% Nb, 0.5% Th, and 0.1% U. Geological and geochemical data show that all rocks in the Burpala massif are derivatives of alkaline magma initially enriched in rare elements. These rocks vary in composition from shonkinite, melanocratic syenite, nepheline and alkali syenites to alaskite and alkali granite. The extreme products of magma fractionation are rare-metal pegmatites, apatite-fluorite rocks, and carbonatites. The primary melts were related to the enriched EM-2 mantle source. The U-Pb zircon ages of pulaskite (main intrusive phase) and rare-metal syenite (vein phase) are estimated at 294 ± 1 and 283 ± 8 Ma, respectively. The massif was formed as a result of impact of the mantle plume on the active continental margin of the Siberian paleocontinent.

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.

This paper presents the results of geochronological studies of the Tomtor alkaline-ultramafic pluton, one of the largest Nb, Y, Sc, and TR deposits. A new scheme of its magmatism is given. The current K-Ar and Rb-Sr ages of different igneous rocks of the Tomtor pluton range from 800 to 250 Ma [Zaitsev et al., 1992; Frolov et al., 2003]. Such dispersion is probably related to the intense carbonatization of the rocks. The U-Pb zircon and 40Ar/39Ar mica ages indicate two stages of the formation of the pluton (700 and 400 Ma), which agrees well with the age of cycles of rift-related tectonogenesis of the Siberian platform.

U-Pb (LA-ICPMS) geochronological studies established the minimum age of detrital zircons from metasedimentary rocks of the Uril Formation of the Amur Group of ∼240 Ma, which approximately corresponds to the lower age boundary of formation of their protoliths. The upper boundary of accumulation of sedimentary rocks of this formation is governed by the age of superimposed structural-metamorphic transformations (220–210 Ma). It follows that the age of protoliths of metasedimentary rocks of the Uril Formation is Triassic in contrast to the previously suggested Early Precambrian age. At the same time, previous estimations of the Nd model age of metasedimentary rocks of the Tulovchikha Formation of the Amur Group and intruding gabbroic rocks are 1.7 and 0.5 Ga, respectively. In other words, the age of this formation is 1.7–0.5 Ga. All of this indicates a combination of sedimentary and volcanic rocks of different ages in the section of the Amur Group. Judging from the Lu-Hf isotopic-geochemical studies of zircons, the major sources of protoliths for metasedimentary rocks of the Uril Formation are Neoproterozoic igneous rocks and also Early and Late Paleozoic and Early Mesozoic igneous rocks, the formation of which was related to the reworking of the Neo- and Mesoproterozoic continental crust.

This paper presents the U-Pb zircon age of pulaskite of the main phase (294 ± 1 Ma) and the rare metal syenite (283 ± 8 Ma) of the Burpala alkaline pluton. The geochronological data show that it was formed in the Early Permian. By age, it is comparable with the Synnyr pluton of the Synnyr rift zone, alkaline granitic rocks and bimodal volcanic associations of the Uda-Vitim rift zone, and carbonatites of the Saizhen rift zone of the Central Asian foldbelt. These intraplate igneous complexes were formed almost simultaneously with crustal granitic rocks of the Angara-Vitim batholite. All of this gives ground to suppose that the origination of their parental melts is a result of the influence of the mantle hot spot or mantle plume on the lithosphere that led to extensive crustal anatexis.

We present results of combined in situ U–Pb dating of detrital zircons and zircon Hf and whole-rock Nd isotopic compositions for high-grade clastic metasedimentary rocks of the Slyudyansky Complex in eastern Siberia. This complex is located southwest of Lake Baikal and is part of an early Paleozoic metamorphic terrane in the eastern part of the Central Asian Orogenic Belt (CAOB). Our new zircon ages and Hf isotopic data as well as whole-rock Nd isotopic compositions provide important constraints on the time of deposition and provenance of early Paleozoic high-grade metasedimentary rocks as well as models of crustal growth in Central Asia. Ages of 0.49–0.90 Ga for detrital zircons from early Paleozoic high-grade clastic sediments indicate that deposition occurred in the late Neoproterozoic and early Paleozoic, between ca. 0.62–0.69 and 0.49–0.54 Ga. Hf isotopic data of 0.82–0.69 Ga zircons suggest Archean and Paleoproterozoic (ca. 2.7–2.8 and 2.2–2.3 Ga; Hfc = 2.5–3.9 Ga) sources that were affected by juvenile 0.69–0.82 Ga Neoproterozoic magmatism. An additional protolith was also identified. Its zircons yielded ages of 2.6–2.7 Ga, and showed high positive e Hf ( t ) values of +4.1 to +8.0, and Hf model ages t Hf(DM) = t Hfc = 2.6–2.8 Ga, which is nearly identical to the crystallization ages. These isotopic characteristics suggest that the protolith was quite juvenile. The whole-rock Nd isotopic data indicate that at least part of the Slyudyansky Complex metasediments was derived from “non-Siberian” provenances. The crustal development in the eastern CAOB was characterized by reworking of the early Precambrian continental crust in the early Neoproterozoic and the late Neoproterozoic–early Paleozoic juvenile crust formation.

The intrusive rocks associated with the large Nezhdaninka gold deposit (Au > 470 t) hosted in the Permian carbonaceous terrigenous sequence have been dated on zircon and rock-forming minerals with precision U-Pb (ID-TIMS) and Rb-Sr methods. The lamprophyre of the dike complex that occurs in the ore field and spatially is related to gold mineralization has concordant U-Pb zircon age (121 ± 1 Ma) and the same isochron Rb-Sr age (121.0 ± 2.8 Ma). The concordant U-Pb zircon age of granodiorite that dominates in the Kurum pluton is 94 ± 1 Ma, whereas the Rb-Sr isochron age of various intrusive rocks from this pluton is 1–4 Ma younger. This difference is caused by long-term cooling of the Kurum pluton and later closure of Rb-Sr isotopic system of biotite (300–350°C) and other rock-forming minerals as compared with U-Pb isotopic system of zircon (∼ 900°C). The Rb-Sr age of quartz diorite from the Gel’dy group of stocks (92.6 ± 0.8 Ma) coincides within uncertainty limits with the age of the Kurum pluton. Thus, the rocks pertaining to two epochs of magmatic activity, which developed in the South Verkhoyansk Foldbelt and divided by a time span of 25–28 Ma, are documented in the Nezhdaninka ore field. Taking into account that the age of gold mineralization is no less than 120 Ma, the data obtained allow us to specify the previously proposed formation model of the Nezhdaninka deposit. These data give grounds to rule out the Late Cretaceous Kurum pluton and the Gel’dy group of stocks from constituents of the ore-magmatic system, and to suggest that an Early Cretaceous deep-seated magma source existed beneath the deposit. Along with host terrigenous rocks, this magma source participated in the supply of matter to the hydrothermal system. The Nd, Sr, and Pb isotopic systematics of igneous rocks and ore mineralization in the Nezhdaninka ore field show that the Early and Late Cretaceous magma sources were formed in the Precambrian crust dated at ∼1.8 Ga.

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.

Among the Caledonides exposed in the western part of the Kyrgyz Range the Lower Ordovician volcanogenic-sedimentary, plutonic, and tuffaceous-terrigenous complexes were distinguished. Volcanogenic-sedimentary sequences are the Kentash Formation, composed of volcanic rocks, tuffs and subvolcanic bodies of dacitic, andesitic and basaltic composition, sandstones and tuffites with interlayers and lenses of limestone. On the basis of conodonts and U-Pb dating of zircon grains the age of this Formation is in the age interval between Late Tremadocian Stage and Early Darriwilian Stage. Differentiated volcanites are associated with ultramafic-gabbro massifs of the Kokkiya Complex of the Late Darriwilian age (U-Pb zirconology). Features of the chemical composition of rocks of the Kentash Formation and the Kokkiya Complex indicate that they formed in suprasubduction settings within the island arc with a thick heterogeneous basement. Tuffaceous-terrigenous deposits are presented by the olistostrome formation, and coarse-grained deposits of the Taldybulak and Kyzylkainar Formations. The formation of olistostrome formation is associated with the over-thrusting of Cambrian melanocratic complexes on terrigenous-carbonate and shale strata of the Upper Precambrian-Cambrian age. Deposits of the Taldybulak and Kyzylkainar Formations accumulated in the back-arc basin and on the island arc slope, made of rocks of the Kentash Formation.

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.

The age of Kuranakh Complex diabases in the western part of the Aldan-Stanovoi Shield determined by the zircon U-Pb method is virtually identical to that of basic rocks in the Chinei stratified pluton and granites in the Kodar Complex. Thus, it is possible to suggest that they form a unified bimodal magmatic association and belong to the South Siberian postcollision magmatic belt, which extends along the southwestern framing of the Siberian Craton for more than 2500 km from the Yenisei mountain range to the Aldan-Stanovoi Shield. The occurrence of the diabase dike swarms in magmatic associations of this belt testifies to formation under lithospheric extension conditions.

The U-Pb zircon dates obtained for the Sutara (480 ± 4 Ma), Kabalinskii (471 ± 10 Ma), and Durilovskii (461 ± 5 Ma) massifs reliably confirm an Early Proterozoic orogenic event, which took place after granulite metamorphism at approximately 500 Ma (Wilde et al., 2003) in the Lesser Khingan (Jiamusi) terrane. The rocks emplaced most shortly after the main metamorphic event are the granites of the Sutara Massif and leucogranites of the Kabalinskii Massif, whose geochemistry is close to that of collision granites. The quartz diorites and subalkaline granites of the Durilovskii Massif, whose geochemistry suggests their origin in a postcollision environment with the participation of an enriched mantle source, were emplaced longer after metamorphic event and after the aforementioned massifs.

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.

This paper presents the results of Sm-Nd isotopic-geochemical and U-Pb geochronological studies of metamorphic (Ilikan Sequence) and associated igneous rocks from the Ilikan lithotectonic zone (terrane) located in the Dzhugdzhur-Stanovoi Superterrane from the Central Asian Foldbelt. The Nd model age, TNd(DM), of metamorphic rocks from the Ilikan Sequence is 2.6–3.2 Ga pointing to the likelihood that the lower boundary of their protolith formation probably does not exceed 2.6 Ga. The age of detrital zircons from metasedimentary rocks of the Ilikan Sequence is 2700–2900 Ma, which absolutely agrees with Sm-Nd isotopic-geochemical results. The U-Pb zircon age of metagabbro that intruded the rocks of the Ilikan Sequence and underwent high-temperature amphibolite metamophism with subsequent structural transformations is 2635 ± 4 Ma. The obtained results allow us to conclude that the age of the Ilikan Sequence is 2630–2700 Ma. All this gives grounds to state that the Dzhugdzhur-Stanovoi Superterrane in the Central Asian Foldbelt was formed due to amalgamation of non-Siberian terranes as is assumed for the Argun, Bureya, and Mamynskii terranes of the Amur Superterrane from the Central Asian Foldbelt.

With U-Pb zircon dating, the ages of the Ul’degit (228 ± 1 Ma) and Chek-Chikan (203 ± 1 Ma) mafic massifs were determined. These massifs were earlier considered to form at the Early Precambrian stage of the geologic evolution of the Dzhugdzhur–Stanovoi superterrane. In geochemical features the igneous rocks of the massifs show relation with a within-plate source, on the one hand, and are similar to igneous rocks of subduction zones, on the other. They might have formed after subduction, which caused the intrusion of gabbroids of the Lucha massif (248 ± 1 Ma) and diorites of the Tok-Algoma complex (238 ± 2 Ma), followed by the fracturing of the subducted plate.

The kinetics of He migration from zircon of variable degree of metamictization was investigated. The migration parameters of He were experimentally determined, the influence of radiation damage and the degree of metamictization on the stability of the (U-Th)/He isotope system was evaluated, the mechanisms of noble gas escape from zircon were investigated, new data on the kinetics of He migration were obtained and compared with previous results for the kinetics of Xe migration from zircon of the same geologic objects. It was shown that He occurs in two energy positions in the zircon lattice: the main position (more than 80% He) with an activation energy of ∼39 kcal/mol and k 0 = 1011 yr−1 and the second position with an activation energy for migration of 5–10 kcal/mol and k 0 ∼ 106 yr−1. It was concluded that He migration from the main energy position is better described by a single-jump mechanism. The migration of He from the second energy position is consistent with the diffusion mechanism. It was shown that deviations from the linear dependence in the lnln(He0/Het)-1/T coordinates are probably related to the destruction of volume defects containing He atoms at high temperatures (more than 1000°C on the experimental time scale) resulting in a change from the single-jump to diffusion mechanism and the presence of atoms migrating via the diffusion mechanism. It was shown that the peak width in the spectrum of radiogenic He release and the appearance of a second peak also depend on the fraction of atoms migrating in accordance with the diffusion mechanism. It was found that the low activation energy for He release from the second energy position indicates the existence of continuous He loss from the zircon lattice.

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.