New data on the U–Pb age (SHRIMP-II) and trace element composition (SIMS) of zircon from gneisses of the Khapchan Group of the Khapchan terrane of the Anabar Shield are presented. Zircon grains contain relicts of magmatic zircon, the protolith and source areas of which are difficult to specify. The only zircon in this group with the least altered core preserved the 207Pb/206Pb protolith age of 1971 ± 19 Ma. During granulite metamorphism, the zircon was subjected to the impact of fluid enriched in incompatible elements. The disurbances affected both the U–Pb isotope system (zircon age was “reset” at metamorphic age of 1920–1930 Ma) and composition of zircon, magmatic cores of which were significantly recrystallized in a solid state or dissolved by fluid up to the practically complete disappearance of primary zircon. In both the cases, zircon was sharply enriched in incompatible elements (Ca, Ti, Pb, Sr, Ba, and some others) owing to fluid effect, while preserved cores seemed to be rimmed by a new zircon population (CL-black). The REE distribution patterns in the recrystallized cores acquired a “bird’s wing” profile atypical for zircon. When the fluid lost its reactivity, the main part of the zircon grain crystallized, typical of granulite zircon. This zircon population is less enriched in incompatible element than the cores are. The horizontal pattern of HREE distribution is consistently repeated, which indicates the co-crystallization of zircon and garnet. The estimated crystallization temperature of the main part of zircon varies in a narrow range of 800–830°C. All zircon domains in the Wetherill concordia diagram form a single trend with a zero lower intercept and an upper intercept confirmed by concordant cluster with an age around 1920–1930 Ma. This value corresponds to the age of regional Paleoproterozoic granulite metamorphism. A unique feature of zircon from the Khapchan gneisses is that its cores did not retain the age marks of the protolith, but were completely reset during metamorphism both in terms of the U-Pb system and the trace element composition, which can be explained by the extremely high intensity of fluid impact during the granulite facies metamorphism superimposed on the rocks of the Khapchan terrane of the Anabar Shield.

An Erratum to this paper has been published: https://doi.org/10.1134/S0016702924190042

Chaotic breccias in carbonate rocks of the Paleoproterozoic Khapchan series of the Anabar Shield were characterized for the first time. Breccias belong to the flysch-carbonate subtype of accretionary olistostrome and confirm the existence of a subduction zone in the Paleoproterozoic in the east of the Anabar Shield. The olistostrome was formed in connection with underwater thrusts during the destruction of an accretionary uplift composed of weakly lithified and loose sedimentary material. The Sm-Nd isotope system of olistostrome rocks indicates a Paleoproterozoic age (TNd(DM2) = 2.34-2.42 Ga) and a juvenile (εNd(T) = 0.6-1.5) proximal nature of the rock source. U-Pb dating of zircon from detrital material and olistostrome matrix constrains the lower temporal boundary of the accretionary stage in the Khapchan Belt. Based on detrital zircon from the carbonate matrix of the olistostrome, the age of accretion is no older than 2009 ± 11 Ma. Granulite metamorphism with an age of 1898 ± 5 Ma is caused by collision events that followed accretion.

The paper gives new data on the geological structure, ore mineralization, composition, petrography, absolute age, petrology and geochemistry of Timofeev stock of Gorny Altai. The absolute age of monzogabbroes of the stock intrusion lower phase is defined as 397 Ma, that corresponds to the Lower Devonian. Nd-model age of protolith during melting of gabbroids composes 893 Ma, that is characteristic of transit zone from the Middle Paleozoic consolidation to the Altai – Mongolian terrain. According to the chemistry, the Timofeev stock rocks belong to the lime-alkali and shoshonite series. The geodynamic aspect of melt generation is interpreted by mixing alkaline oceanic basalts of the plume setting and normal oceanic basalts of mid-oceanic ridges that took place in the Paleo-Asian Ocean evolution in the Early Paleozoic. Samarium-neodymium isotopic labels of gabbroids indicate the proximity of their values to chondrite meteorites. The ratio of neodymium isotopes with gabbro age indicates that the isotopically varying earth’s crust, close to the depleted mantle, existed under the Korgon trough in the Early Paleozoic. The skarn-iron-ore deposit of the same name is spatially and paragenetically connected with the Timofeev stock.

Granulite complex on the left side of the Bol. Kuonamka River, below the mouth of the Khapchan River, is composed of melanocratic and mesocratic orthopyroxene–clinopyroxene crystalline schists and leucocratic orthopyroxene and orthopyroxene–clinopyroxene plagiogneisses. The granulites formed after mafic to felsic volcanoplutonic rocks with rare sedimentary interlayers. In terms of chemical composition, the mafic and ultramafic rocks correspond to pyroxenites, gabbronorites, and gabbro-diorites of the tholeiite series. The plagioschists and plagiogneisses were formed after rocks similar to diorites, tonalities, and trondhjemites or their volcanic analogs, and are distinguished by increased contents of Ba, Zr, Y, REE, Nb, and Ta. The concordant U-Pb age of zircon from the diorite protolith of orthopyroxene–clinopyroxene plagioschists is 2095 ± 10 Ma. The Lu-Hf isotopic composition of the zircon (εHf (T) = 6.5–12, THf(DM) = 1.98–2.22 Ga) indicates the correspondence of its source to the Paleoproterozoic depleted mantle. Two-pyroxene plagiogneisses with a concordant U-Pb zircon age of 2030 ± 17 Ma were formed after tonalites of the calc-alkaline series. They are characterized by well-pronounced negative Ti, Nb, Ta, P anomalies characteristic of subduction magmatism. All studied rocks of the Khapchan Belt have positive εNd(T) values from +2.3 to +4.2 and are interpreted as a juvenile suprasubduction complex. It is assumed that the subduction of oceanic crust of this age is associated with the formation of eclogitic diamond, which was noted earlier and widespread in placer deposits in the northeastern Siberian platform.

New data on phase relationships, petrology and geochemistry of the Sinyukhinskoye rocks and dikes of the same deposit are presented. Five phases of rock intrusions formed in a homodromic-antidromic sequence are found. The Sinyukhinskoye rocks fall in the oxidized type. In the depth, a source of melting was garnet lherzolites, and, to a lesser extent, spinel lherzolites of an enriched mantle source of the lithospheric slab with a degree of partial melting from 0.2 to 0.4 and low pressure. The formation of intrusive rocks of the deposit took place in the post-collisional environment. The magmatite fluids of the massif and dikes were characterized by high partial pressures of such volatile components as H2O, Cl, F, CO2, which were the main carriers of metals. The rocks exhibit the tetrad effect of the W-type REE fractionation. The dependences of the values of the latter and the concentrations of copper and gold in igneous rocks and fluids were determined by different regimes of acidity and alkalinity of the medium. The deposit belongs to a complex family of ores of the copper-gold-skarn-porphyry type. In the Cheryomukhovaya Sopka and Chir areas, this is also confirmed by the presence of the copper-gold-porphyry type in the ore field, in addition to the gold-copperskarn mineralization.

In the northern part of the Anabar Shield, orthopyroxene plagiogneisses of the granulite Daldyn Group host lenses of mafic rocks surrounded by melanocratic rims. According to their chemical composition, the mafic rocks correspond to subalkaline gabbro, the plagiogneisses correspond to granodiorites contaminated with mafic material, and the rims are diorites. The orthopyroxene plagiogneisses of granodiorite composition have 147Sm/144Nd = 0.1097, εNd(Т) = 1.6, TNd(DM) = 3.47 Ga and are metamorphosed anatectic granitoids with an age of 3.34 Ga. The mafic rocks have high Zr, Th, and Pb contents, are enriched in REE (ΣREE = 636 ppm), with a high degree of fractionation [(La/Yb)N = 17.73] and a well-defined Eu minimum (Eu/Eu* = 0.51), and have 147Sm/144Nd = 0.099, εNd(Т) = 1.4 and TNd(DM) = 3.65 Ga. It is assumed that these rocks crystallized from melt derived from an enriched mantle (plume) source. Based on U–Pb (SHRIMP-II) dating of 50 zircon grains from the mafic rocks, a group of grains with concordant ages from 3567 to 1939 Ma was distinguished, along with a large number of discordant values. Multiple measurements in zircon grains with discordant age values make it possible to identify seven grains of Eoarchean age, with upper intercepts of the discordia corresponding to 3987 ± 71 to 3599 ± 33 Ma. The Lu–Hf systematics of 14 zircon grains is characterized by εHf(T) = +3.7 and by close values of THf(DM) = 3.95 and $${\text{T}}_{{{\text{Hf}}}}^{{\text{C}}}$$ = 3.93 Ga (3.99 Ga for the oldest zircon). The Paleoarchean (3.57 Ga) zircons are characterized by negative values of εHf(T) = –5.3 and –6.8, THf(DM) = 3.92–3.98 Ga, and $${\text{T}}_{{{\text{Hf}}}}^{{\text{C}}}$$ = 4.14–4.24 Ga, which indicate recycling of the preexisting Eoarchean and Hadean continental crust. The younger zircon (3287–2410 Ma) was also formed when the preexisting crust was recycled.

The paper presents U–Pb zircon dates (SHRIMP-II) and isotopic-geochemical data (SIMS and Sm–Nd method) on detrital zircon and its sedimentary host rocks of the Daldyn Group at the Anabar Shield. The rocks were metamorphosed to the granulite facies. The oldest Eoarchean (3.7 Ga) source of terrigenous material (determined based on single zircon grains) is confirmed by the Nd model age of the protolith: TNd(DM)2 = 3.69–3.71 Ga. The rocks are dominated by zircon dated at 3.5 Ga, which reflects that the area from which the terrigenous material was brought consisted mostly of Paleoarchean magmatic rocks.

Представлены результаты геологических, геохимических и изотопно-геохронологических исследований субвулканических риолитов Западного Горного Алтая и Рудного Алтая, принадлежащих двум крупным герцинским вулканическим системам, Алтае-Минусинской и Алтае-Салаирской. Результаты изотопного U-Pb-датирования цирконов показали две группы возрастов: ~410-405 и 390-381 млн лет. Изотопно-геохимические характеристики риолитов демонстрируют высокие значения e Nd ( Т ) = +2,7…6,0 с относительно молодыми значениями модельных возрастов T (DM) = 851-966 млн лет в Рудном Алтае и более древними - до 1266 млн лет в Горном Алтае. Петрогеохимические характеристики указывают на принадлежность составов риолитов к пограничной области между внутриплитными и островодужными кислыми магмами. Полученные результаты соответствуют двухстадийной эволюции вулканизма и его миграции от континента к океану.

The paper presents the results of geological, geochemical and isotope-geochronological studies of subvolcanic rhyolites of the Western Gorny Altai and Rudny Altai which have related to two large volcanic systems, the Altai-Minusinsk and Altai-Salair, respectively. The results of U-Pb isotopic dating of zircons revealed two groups of ages ~410-405 and 390-381 million years. Isotope-geochemical characteristics of rhyolites show relatively high values of εNd(T) = +2,7...6,0 with relatively young values of model ages T(DM) = 851-966 Ma in the Rudny Altai and more ancient - up to 1266 Ma in the West Gorny Altai. Geochemical characteristics indicate that its composition is consistent with transitional field between within-plate and island-arc felsic magmas. The results obtained correspond to the two-stage evolution of volcanism and its migration from the continent to the ocean.

The paper presents the results of the isotope, geochemical and thermobarometric study of plagio-crystalline schist containing in the Upper Anabar series of the Anabar Shield. Granulite complexes of the paleoplatforms are the most important issue in addressing the fundamental problem of the Earth's crust origin and its composition. The early stages of crust formation which correspond to the deeply metamorphosed rocks of the platform basements, available for study within the shields, are of particular interest. The study of the age and metamorphic conditions of granulites by the case of the Upper Ananbar series allows specifying the stages the Anabar Shield's ancient crust formation. Isotope-geochemical (U-Pb geochronology for zircon and Sm-Nd for garnet-amphibole-WR) and thermoba-rometric (Theriak-Domino) studies of plagio-crystalline schist allowed to identify two Paleoproterozoic metamorphism stages within the territory of the Anabar Shield with an age of about 1997 and 1919 million years. The peak conditions of granulite metamorphism are determined as 775±35 С and 7.5±0.7 kbar, the parameters of the regressive stage are 700 C and 7 kbar. The sequence of the rocks metamorphic transformations can be assumed: high-thermal metamorphism of the granulite facies (T ≤ 810 C) and subsequent sub-isobaric (about 7 kbar) cooling to 700 C with a water activity increase and formation of Grt-Amp paragenesis corresponding to the transition from the granulite to amphibolite facies. Data on the REE and other trace elements distribution in zircon and rock-forming minerals obtained by the ion microprobe analysis contribute significantly to the isotope-geochemical data interpretation.

The Hf-Nd isotope systematics was used to determine the genesis of zircons from granulites of the Daldyn Group of the Anabar Shield. Obtained age of magmatic crystallization for biotite–hypersthene crystalline schists and garnet amphibolites agree with position of zircons within terrestrial array. Magmatic genesis of plagiogranite neosome under granulite conditions was established for leucocratic plagiogneisses.

The relevance of the discussed issue is caused by the need of researching absolute age, petrology, geochemistry and ore mineralization of Tochilny stock which is represented by strong fractionated rocks from melanosienite to leucogranite. Different types of ore mineralization of rare earth pegmatites and juweller-ornamental stones are related to such rocks spatially and paragenetically. The main aim of the research is to study absolute age, petrology, geochemical features of rocks and ore mineralization of Tochilny stock using the experimental diagrams, which allow solving the genetic problems and the physic-chemical features of petrogenesis. The methods used in the study. Rare and scattered elements were determined in rocks by inductively coupled plasma method on the mass spectrometer «ОРTIMA-4300», the rest elements, including REE, were determined by La-ISP-MS methods in the Laboratory VSEGEI (Saint-Petersburg) and OIGaG SO RAN (Novosibirsk). The absolute age of forming rocks was determined by U-Pb SIMS (ion microzond SHRIMP -II) method on zircon in the Laboratory VSEGEI (Saint-Petersburg). Results. The paper introduces the data on absolute age, geochemistry and petrology of granitoids of Tochilny stock and its ore mineralization. Melanosyenite, syenite, granite-porphyre and leucogranite were revealed in the stock. Stock formation lasts for prolong period in 24 mln. years (from 238 to 262 mln. years). So long period of forming caused by combining derivates of high-K shoshonitic series rocks and high-K adakite-like differences in one stock. Considering the Nb/Ta ratio in rocks one can assume melting of amphibole-contenting source, meeting the high-Nb basalts (NEB) of thickened lower earth crust. This subcontinental lithospheric mantle, transformed by basalt magmas, generated at subduction ocean lithosphere melting, was transformed under the effect of plume source. Rare metal pegmatites, related to granitoids of Tochilny stock, refer to the Nb>Ta-Y-F (NYF) family. According to the geochemical data pegmatites refer to rare earth elements class (REE) enriched with Zr, Ta, Nb. The tetradic effect of REE M-type fractionation occurs in syenites.

The relevance of the discussed issue is caused by the need of researching petro-geochemistry and petrologic peculiarities of gabbrogranitoid complexes which are related with gold-copper-skarn ore mineralization. The main aim of the research is to study geochemistry of rock types of Topolninsky complex in Gornyn Altai using canonic classification and experimental diagrams on genesis and petrology of magmatites. The methods used in the study. Chemical composition on the major petrogenic elements was determined by silicate assay by X-ray fluorescence (XRF) techniques. Rare elements were determined by inductively coupled plasma on the mass spectrometry «ОРTIMA-4300», for Cu, Zn, Pb, Li - by methods of ISP-AES, the rest elements, including REE wre determined by ISP-MS methods in the VSEGEI Laboratory (St-Petersburg). Absolute age of granitoids was defined by U-Pb method SHRIMP II on zircon in the VSEGEI Laboratory (St-Petersburg). Results. The authors have corrected the absolute age of granitoids formation in Topolninsky complex. For Topolninsky massif by 10 point it is 397,4-4,4 million years, for Karaminsky massif it is 399,3-4,6 million years, corresponding to a border of Lower and Middle Devonian. The paper describes a direct zoning in Karaminsky massif formation. More evolution phases of leucogranites in it are located in the center of massif but early gabbros are on the periphery. The authors estimated different petrochemical coefficients, indices, modules for the rocks of the complex used for decoding the genesis. The ratios of strontium isotopes (87Sr/86 Sr for granodiorites of Topolninsky massif is 0,70556, but for Karaminsk leucogranites is 0,70618) identify mantle nature of melts, formed with crust material contamination. The paper indicates the space and paragenetic relation of different types of ore mineralization with granitoids of Topolninsky complex.