In numerous orogenic belts, A-and I-type granitoids may coexist within a single pluton or intrusive series. These granitoids may be semi-contemporaneous and exhibit converging chemical signatures, implying similar petrogenetic histories. However, compositionally similar plutons may mark different tectonic settings. A notable example is observed in the Late Paleozoic granitoids of the Trans-Altai Gobi (SW Mongolia). Two temporally discrete stages of A-and I-type granitoids were identified here through zircon U-Pb and amphibole 40Ar-39Ar dating: Late Carboniferous (ca. 317 Ma) and Early Permian (295-283 Ma). The Late Carboniferous granitoids are hypersolvus A-type, containing aegirine with alkali amphibole, and are associated with a bimodal volcanic sequence. The Early Permian granitoids include subsolvus I-type and hyper-and transsolvus A-type, containing Ca-Na amphibole and/or biotite, but lacking aegirine. Gabbroid enclaves and mafic dikes were observed within one of these plutons. The mafic rocks exhibit chemical signatures similar to those of intraplate basalts, suggesting a potential origin from the asthenospheric mantle with addition of the subduction-modified lithospheric material. The Late Carboniferous and Early Permian A-and I-type granitoids exhibit a similar Nd isotopic signature (epsilon Nd(t) from +5.5 to +6.8), which correspond to the ranges of the Hercynian crustal isotope province and the values observed in the associated mafic rocks. However, the distinct chemical characteristics of mafic and salic rocks preclude common origin. We propose a similar petrogenetic scenario for the Late Carboniferous and Early Permian granitoids inferred in partial melting of earlier calc-alkaline subduction-related granitoids. Due to low melting degree, the Late Carboniferous A-type rocks are relatively enriched in incompatible Nb, Ta, REE, Zr, and Hf, but are strongly depleted in Ba, Sr, and Eu, which were preferentially partitioned into residual plagioclase and K-feldspar. An increased degree of melting in the Early Permian promoted the formation of both A-and Itype granitoids were not enriched in incompatible elements and moderately depleted in Ba, Sr, and Eu. The studied granitoids record two different tectonic stages of crustal extension in the Trans-Altai Gobi, adjacent Eastern Junggar, and western Central Asian Orogenic Belt (CAOB) as a whole. The Late Carboniferous A-type granitoids and bimodal volcanics were emplaced immediately after the termination of Early Carboniferous subduction-related magmatism and mark a short-term post-accretionary stage following the closure of the South Gobi-Kelameili branch of Paleo-Asian Ocean. The Early Permian A-and I-type granitoids belong to an episode of widespread anorogenic magmatic activity covering various terranes in the western CAOB. This magmatism could be initiated by thermal expansion from the Tarim mantle plume into the CAOB area and/or by delamination/dripping of the lower continental crust, which was thickened due to prior multiple accretions of terranes sandwiched between the Tarim and Siberian cratons.

The Trans-Altai Gobi (TAG) in southern Mongolia is considered one of the largest tectonic structures within the Central Asian Orogenic Belt, formed by island-and back-arc magmatism in the Middle-Late Paleozoic Paleo-Asian Ocean (PAO). Although the island-arc origin of certain TAG ophiolites is well established, the back-arc nature of others remains unproven owing to the lack of reliable geochemical and isotopic data. The Altan Uul (AU) ophiolite complex, located in the westernmost Nemegt Ridge of the eastern TAG, has previously been interpreted as a remnant of back-arc oceanic crust, rendering petrological studies of the AU essential for understanding the mantle sources and geodynamic processes of the PAO in the Middle-Late Paleozoic. The AU ophiolite comprises the Late Silurian-Early Devonian tholeiitic and calc-alkaline gabbros and basalt-dacite-rhyolite volcanics metamorphosed in greenschist facies. AU rocks can be divided into two groups according to their trace element patterns: one exhibiting island-arc basalt (IAB)-like characteristics and the other showing mid-ocean ridge basalt (MORB)-like signatures. Rocks from both groups are depleted in light rare earth elements (La-N/Yb-N = 0.1-0.9) and demonstrate very high epsilon(Nd(t)) (+8.0-+10.2), along with generally low Sr-87/Sr-86(t) (0.70262-0.70443), Pb-206/Pb-204(t) (17.158-17.665), and Pb-207/Pb-204(t) (15.371-15.447) ratios. These geochemical and isotopic features of ophiolitic rocks indicate that they originated from two sources: subduction-modified depleted mantle and depleted mantle. The progressive enrichment in trace elements from basalts to rhyolites, coupled with their similar Sr-Nd-Pb isotopic compositions, suggests that felsic rocks formed through the differentiation of mafic melts. The identified mantle sources of igneous rocks and subordinate role of cherts in the AU structure imply that the AU ophiolite formed in a back-arc basin. As a PAO domain, this basin separated the TAG island-arc system from the Altai active continental margin of Siberia during the Middle Paleozoic. The AU ophiolite is intruded by unmetamorphosed plagiogranites with a zircon SHRIMP age of 344 +/- 3 Ma. Plagiogranites have low K content and combine IAB-and MORB-like trace elements (LaN/YbN = similar to 1.4) and isotopic (epsilon(Nd(t)) = +9.2, Sr-87/Sr-86(t)= 0.70443, Pb-206/Pb-204(t)= 17.671, and Pb-207/Pb-204(t)= 15.431) signatures. These findings suggest that plagiogranites formed via melting of AU ophiolitic rocks or similar mafic rocks of the TAG basement when the area was subjected to Early Carboniferous continental margin magmatism. Our data support the hypothesis that closure of the AU back-arc basin and accretion of the TAG island-arc to the Altai peri-Siberian continental margin occurred by the earliest Carboniferous.

The paper discusses the melt sources and formation parameters of the Khokhol-Repyevka granitoid batholith that compose the Don terrane of the Volga–Don orogen in the East European craton. The batholith consists of three granitoid types: Pavlovsk granitoids (quartz monzonites–granites, mostly without pyroxenes), Potudan granitoids (quartz monzogabbro–granodiorites containing pyroxene), and hybrid ones (quartz monzodiorites, monzonites, and quartz monzonites). These three types of rocks occur together and have a similar age of 2050–2080 Ma, similar geochemical characteristics (high contents of Ba, Sr, and highly fractionated REE patterns with GdN/YbN = 2–11), but differ in petrographic and isotopic geochemical parameters. The initial isotope characteristics of the sources of the Pavlovsk-type rocks are εNd(t) = +0.2 to ‒3.7 and Sri = 0.70335, those of the Potudan type are εNd(t) = –1.7 to –3.8, Sri = 0.70381–0.70910, and the hybrid rocks have εNd(t) = –8.8, Sri = 0.70596. In addition to granitoids, the batholith was found out to host two types of leucogranite dikes. One of them is characterized by εNd(t) = –3.8 and fractionated HREE patterns (GdN/YbN = 2.1–3.8) and could be formed as a result of the deep differentiation of Pavlovsk-type magma. The other type has εNd(t) = –7.8 and less fractionated HREE patterns (GdN/YbN = 1.1–1.6), which likely resulted from the melting of a crustal source at shallow depths. The Rb–Sr isotope-geochemical characteristics of rocks of the Pavlovsk and Potudan types indicate that their melts were derived from different sources. Therefore the melts of the Khokhol–Repyevka batholith were derived from at least three sources: (1) lower (or buried oceanic) crust of predominantly mafic composition and/or enriched mantle, which was metasomatized in the Proterozoic, whose involvement is reflected in the composition of the Pavlovsk granitoids; (2) an enriched mantle source, which was likely subcontinental lithospheric mantle (SCLM) that had been metasomatized during an earlier stage of the geological development of the region, specific of the Potudan-type monzonitoids; and (3) Archean crust consisting mostly of TTG gneisses and metasediments, which underwent melting and participated in the formation of some of the leucogranite dikes and hybrid rocks. The results of thermodynamic modeling indicate that the mixing of two melts contrasting in composition (Potudan-type mafic and Pavlovsk-type intermediate–felsic) could form only some of the hybrid rocks. The others could be formed by mafic melt contaminated with anatectic melts derived from the Archean crust of the Kursk block.

The paper presents results of research into the conditions of formation of ores in the poorly studied Algama ore cluster (Bodorono deposit and Dyvok ore occurrence) located at the junction of the Aldan Shield and the Stanovoi area. We have established that Bi and Se minerals (bismuthinite, lillianite, native bismuth, tellurobismuthite, tetradymite, hedleyite, pilsenite, and laitakarite) are present in the ores of the Bodorono deposit. Two successive productive stages of mineral formation have been distinguished: Au-polymetallic and Au-Bi-Te. The corresponding minerals are products of the evolution of a hydrothermal system, during which a gradual decrease in fluid temperature (from 300 to 145 degrees C) and salinity (from 5 to 1.9 wt.% NaCl equiv.) took place. The fineness of native gold gradually increases from early (similar to 840 parts per thousand) to late (similar to 940 parts per thousand) stages and changes in passing from simple sulfides to sulfosalts. The evolution of the ore system is accompanied by a change in the composition of the vapor phase of fluid inclusions from CH4-CO2 to CO2 with an impurity of N-2 and CH4. The results of Ar-40/Ar-39 dating of pre-ore metasomatites point to ore-forming processes at the Bodorono deposit ca. 150 +/- 1.8 Ma. Analysis of the isotopic composition of lead in galena shows the leading role of the ancient crustal source of ore matter. The calculated isotopic composition of oxygen (delta O-18(H2O)) in ore-bearing quartz varies from 1.0 to 7.3 parts per thousand, which corresponds to an aqueous fluid of a mixed source. The Dyvok ore occurrence differs from the Bodorono deposit in the mineral composition of ores and the physicochemical parameters of ore formation. Four mineral stages have been established within the ore occurrence: gold-arsenopyrite-pyrite-quartz, pyrite-chalcopyrite-sphalerite, quartz-boulangerite, and telluride. The telluride stage is represented by hessite, altaite, volynskite, merenskyite, melonite, and rucklidgeite. Gold-bearing mineralization formed from a fluid of medium salinity (0.9-9.2 wt.% NaCl equiv.) with a predominance of CO2 and an impurity of CH4 in the vapor phase at moderate temperatures (310-360 degrees C). The calculated values of delta S-34 and delta O-18 varied from 2.2 to 3.0 parts per thousand and from 0.6 to 12.0 parts per thousand, respectively. The Ar-40/Ar-39 age of gold mineralization is 124.0 +/- 1.5 Ma, which corresponds to the stage of tectonomagmatic activity in the Aldan Shield.

The paper presents the results of study of Rb–Sr isotopic system of ore-hosting granitoids, metasomatites after granites, and hydrothermalites of the Upper Karalon gold deposit, as well as the Pb–Pb isotopic system of galena of low-sulfide gold–quartz mineralization of the Karalon gold field. Three groups of ore objects with various Pb isotopic composition of galena are distinguished. Different contribution of mantle and ancient crustal sources is identified for each group. The Pb isotopic composition of galena of the Upper Karalon deposit indicates its genetic link with ore-hosting granites, the age of which (∼600 Ma) could be close to the age of the earliest stage of formation of gold–quartz mineralization. The ancient crustal source is common for the leading gold deposits of North Transbaikalia and exhibits the continental crust parameters of the Siberian Craton at the period of 500–600 Ma. It is established that the Rb–Sr system of the studied rocks and minerals of the Upper Karalon deposit was reconstructed and the Pb isotopes of galena of the Vodorazdel’naya ore zone of the Karalon ore field were redistributed at the boundary of 290–250 Ma. The isotopic data show that the processes of the formation of gold mineralization in geological evolution of the Upper Karalon deposit and Karalon ore field were characterized by long multistage character and accompanied by the regeneration of primary ore concentrations.

We present the results of Nd and Pb isotope studies of late Neoproterozoic-early Paleozoic granitoids of the Kaa-Khem batholith, which formed in different geodynamic settings within the early Caledonian structures of Eastern Tuva (Altai-Sayan sialic area). Based on the obtained isotope data, we assess the role of different source materials in the formation of melts for these granitoids and compare these rocks with coeval granitoids from the Lake Zone of Mongolia. The plagiogranitoid associations of the island arc stage of the Kaa-Khem batholith formation (572-562 Ma) are characterized by mantle Nd isotope values. In contrast, the Pb isotope characteristics of these intrusive associations correspond to an upper-crust source formed predominantly by terrigenous sediments. The granitoid associations of the accretion-collision stage of the Kaa-Khem batholith formation (512-450 Ma) have a less radiogenic primary Pb isotope composition as compared with the island arc granitoids. Evidently, during the magma formation at this stage, the relative role of terrigenous material decreased, while the role of depleted mantle material increased. At the same time, the decrease in epsilon Nd values in the granitoids as compared with the depleted mantle indicates that, along with the upper-mantle component, the role of the lower-crust component increased. These Nd and Pb isotope characteristics of the accretionary granitoids of the Kaa-Khem batholith indicate a significant contribution of the lower-crust source to their formation. This source is the crystalline basement of the Tuva-Mongolian microcontinent. The Pb isotope characteristics of the accretion-collision granitoids of the Kaa-Khem batholith are shifted to the upper-crust compositions relative to those of the Lake Zone granitoids. The reason is that the latter formed predominantly through the transformation of early Caledonian island arc complexes, which were generated with a higher portion of mantle component.

Late Neoproterozoic Arbarastakh alkaline ultramafic carbonatite-phoscorite complex in the southern margin of the Siberian craton (Aldan-Stanovoy shield), includes carbonatites and phoscorites closely associated with pyroxenites-ijolites and ultramafic lamprophyres. Major and trace elements data, Sr, Nd and Pb isotope com-positions for the Arbarastakh rocks have been obtained to characterize the sources involved in their formation, primary melt composition and to build the petrogenetic model.All rock varieties, excluding nepheline syenites, are characterized by incompatible elements enrichments, including light rare earth elements, and strong fractionation of REEs. The initial isotope ratios of the analyzed samples, calculated at 645 Ma, display limited variations: epsilon Nd from +5.9 to +6.9 and 87Sr/86Sr from 0.70225 to 0.70272, excluding nepheline syenite with epsilon Nd +5.4. The initial Pb isotope ratios for the most studied samples overlap with each other within uncertainties. They yield an age of 642 +/- 5 Ma. The Nd and Sr isotope data of the Arbarastakh rocks generally fit the patterns of the other Neoproterozoic alkaline ultramafic carbonatite com-plexes of the southwestern and southern margins of the Siberian craton. Observed Sr, Nd and Pb isotope vari-ations indicate mixing of the asthenosphere and the depleted mantle components.It is supposed that the primary melts for the Arbarastakh rocks were generated directly by low-degree melting of metasomatic phlogopite-carbonate veins with apatite and Ti-oxides in garnet peridotite, which formed shortly before the onset of melting. Ultramafic lamprophyre (aillikite) is closest to the primary melt composition in terms of high #MgO, Cr and Ni. The aillikite and latter pyroxenite crystallized from primitive melt by fractionating the olivine, phlogopite and clinopyroxene dominated mineral assemblage that was free of feldspar. This fractionation forced Na-enrichment in the magmas resulted in liquid silicate-carbonate immiscibility. Major and trace element and isotope data indicate that the nepheline syenites are unlikely to be related with other alkaline silicate rocks through fractional crystallization and could have been formed through pre-emplacement interaction with the ambient crustal materials. Emplacement of calcite carbonatites resulted in metasomatism of surrounding py-roxenites with formation of clinopyroxene-phlogopite-calcite carbonatites. Subsequent portions of Fe-P-enriched carbonatite magmas crystallized phoscorites and apatite-dolomitic carbonatites.

The results of systematic geochronological (K–Ar) studies of rocks of the Dariganga volcanic field (DVF) composed of Late Cenozoic mafic lavas are presented. Four stages of its evolution are distinguished: the Middle–Late Miocene (>10 Ma), Late Miocene–Early Pliocene (7.8–3.5 Ma), Late Pliocene (2.8–2.6 Ma), and Pleistocene (<1.7 Ma). The products of these stages are regularly distributed within the volcanic field. The main volume of eruptions was related to the Late Miocene–Early Pliocene and Pleistocene stages. The northwestern part of the lava field as a lava plateau formed during the Late Miocene–Early Pliocene. The eruptions are related to a local structural depression, which originated under extension accompanying volcanism. The southeastern part of the DVF formed during the Pleistocene volcanic eruption. Volcanism accompanied the formation of the Khukhot-Ein-Nuru Ridge in the Nukut-Daban Uplift and was responsible for the morphological peculiarities of the volcanic cover. A typical feature of it includes the large multicentered shield volcanoes related to the axial zone of the ridge, as well as the elongated valley flows along both slopes. The peculiarities of the formation of the DVF and other volcanic areas of the Late Cenozoic intraplate volcanic province of Central and East Asia are compared. Their consistent evolution indicates that the formation of the DVF was controlled by the same geodynamic mechanisms as the formation of other volcanic areas of the province, namely, by the activity of a small mantle plume.

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during ~1.88–1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650–700 °C at 1.88–1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300–400 °C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.

Geochronological (U-Pb on zircons, ID-TIMS), isotope-geochemical (Nd, Sr, Pb), and geochemical studies of rocks of the Amanan and Amudzhikan intrusive complexes and volcanic rocks of the Ukurey Suite in the eastern part of the West Stanovoy superterrane of the Central Asian Fold Belt were performed. The belonging of granitoids of these complexes to high-potassium C-type adakites is substantiated. The cogeneticity of the studied rocks has been established, which makes it possible to unite them into one Amudzhikan volcano-plutonic association formed in the age range of 133±1–128±1 Ma. The igneous complexes of this association are part of the Stanovoy volcano-plutonic belt, which extends in the sublatitudinal direction from the Pacific Ocean deep into the North Asian continent for more than 1000 km subparallel to the Mongol-Okhotsk suture zone and stitches the tectonic structures of the Dzhugdzhur-Stanovoy and West-Stanovoy superterranes. The formation of the Stanovoy Belt is connected with the closure of the Mongolo-Okhotsk Ocean and the collision of the continental masses of the North Asian and Sino-Korean continents at the turn of ~140 Ma. The subsequent collapse of the collisional orogen, accompanied by large-scale lithospheric extension and delamination of the lower part of the continental lithosphere, led to upwelling of the asthenospheric mantle. This caused the melting of the lithospheric mantle and continental crust and, as a consequence, the formation of both mafic melts of the shoshonite type and anatectic crustal melts of the adakite type. The mixing of these melts led to the formation of the parent magmas of the Amudzhikan magmatic association. The crustal component in the source was of a heterogeneous nature and was finally formed as a result of the Early Cretaceous collision event. It is characterized by upper-crustal isotopic parameters: an increased Rb/Sr and U/Pb ratio and a decreased Sm/Nd ratio in the source. The mantle component is represented by the material of the enriched lithospheric mantle of the Central Asian fold belt, the formation of which is associated with subduction processes at the stage of closure of the Mongol-Okhotsk paleoocean. Metasomatic transformation of the mantle with the introduction of melts and fluids with isotopic parameters of an EMII-type source or upper crust occurred at this stage.

The paper discusses the possible conditions and involvement of sources in genesis of the Khokhol-Repyevka batholith granitoids, that build up the Don terrane in the Volga-Don orogen of the East European Craton. In the batholith, three types of granitoids are distinguished – pavlovsk (quartz monzodiorite–granites, mainly pyroxene-free), potudan (quartz monzogabbro–granodiorites containing pyroxene) and hybrid (quartz monzodiorites, monzonites, quartz monzonites). These three types of rocks are spaсely co-located and have a similar age of formation 2050–2080 Ma, similar geochemical characteristics (high contents of Ba, Sr, highly fractionated REE patterns (GdN/YbN= 2–11)), however, they differ in petrographic and isotopic geochemical parameters. Primary isotope characteristics of sources for rocks of the pavlovsk type εNd(t) = +0.2…–3.7, Sri= 0.70335, for potudan εNd(t) = – 1.7 ... –3.8, Sri= 0.70381–0.70910, for hybrid εNd(t) = – 8.8, Sri= 0.70596. Apart from granitoids, two types of leucogranite dikes were found in the batholith. The first type is characterized by εNd(t) = –3.8 and fractionated HREE patterns (GdN/YbN= 2.1–3.8) and could have formed as a result of deep differentiation of pavlovsk-type magma. The second type is with εNd(t) = –7.8 and less fractionated HREE patterns (GdN/YbN = 1.1–1.6), which presumably appeared as a result of melting of a crustal source at shallow depths. Rb-Sr isotope-geochemical characteristics of rocks of the pavlovsk and potudan types indicate their formation from different sources. In total, at least three sources took part in the formation of the Khokhol-Repyevka batholith: 1) lower (or buried oceanic) crust, predominantly of mafic composition and/or enriched mantle, metasomatized in the Proterozoic, the participation of which is reflected in the composition of the Pavlovsk granitoids; 2) an enriched mantle source, probably represented by subcontinental lithospheric mantle (SCLM), possibly metasomatized during the previous stage of geological development of the region, specific for Potudan-type monzonitoids; 3) Archean crust, consisting mainly of TTG gneisses and metasediments, which underwent melting and participated in the formation of part of the leucogranite dikes and hybrid rocks. The results of thermodynamic modeling indicate that the mixing of two melts contrasting in composition – mafic (potudan-type) and intermediate-felsic (pavlovsk-type) can lead to the formation of only part of the composition of hybrid rocks. The formation of the rest was influenced by the contamination of mafic melt by anatectic melts from the Archean crust of the Kursk block.

The Early Proterozoic gabbros of the Velimyaki intrusion of the Northern Ladoga region contain titanomagnetite ore, which has been mined as early as the end of the 19th century. Titanomagnetite horizons are enriched in phosphorus in form of apatite reaching 10 vol

The Mesozoic magmatic activation in Central and Northeast Asia resulted in the formation of a large volume of volcanic rocks with diverse compositions. The most dramatic compositional change occurred at the end of the Early Cretaceous, when mainly alkaline basaltic lavas began to erupt after subalkaline differentiated lavas. The nature of crustal and mantle processes that led to this change in volcanism remains unclear. The Torey Volcanic Field (TVF) of Eastern Transbaikalia (Russia) demonstrates a similar compositional change. Therefore, the TVF is crucial to studying the cause of the difference in geochemical and isotopic signatures of the Mesozoic volcanism in Central and Northeast Asia. TVF belongs to the northeastern end of the Eastern Mongolia Volcanic Area (EMVA). Like other volcanic fields of the EMVA, TVF formed in two stages: early (similar to 121-129 Ma) and late (similar to 101-119 Ma). The TVF is composed of subalkaline and alkaline basaltic trachyandesites - trachyandesites. All TVF rocks are characterized by negative Ti and Sr anomalies and positive Ba and Pb anomalies. Compared to the late TVF rocks, the early TVF rocks have distinct negative Ta and Nb anomalies and are highly enriched in light rare earth elements relative to heavy rare earth elements. TVF rocks have the following isotopic characteristics: Sr-87/Sr-86((t)) = 0.70477-0.70540, epsilon(Nd(t) =) - 0.9 - +2.4, Pb-206/Pb-204((t)) = 17.9-18.4, and Pb-207/Pb-204((t)) = 15.5-15.6. However, older rocks mainly have higher epsilon(Nd(t)) values and Pb-206/Pb-204((t)) and Pb-207/Pb-204((t)) ratios. Geochemical and isotopic data of samples suggest that the TVF formed by melting in the continental metasomatized lithospheric mantle (CMLM). Phlogopite-amphibole-rutile-bearing pyroxenite veins played a major role in the formation of older rocks. Eclogite, represented by the recycled oceanic crust or the buried lower continental crust, was dominant in the source of younger rocks. The common source for both groups of the TVF rocks was metasomatized hydrous peridotite. Lithospheric extension and subsequent asthenospheric upwelling led to melting in the CMLM and the formation of the TVF. At the early stage of the volcanism, melting occurred at relatively low temperatures where amphibole, phlogopite, and rutile were stable. Due to ongoing lithosphere extension, the melting of eclogite occurred at a higher temperature and/or lower pressure at the late stage of the volcanism.

For the first time, the U–Pb and Rb–Sr age of granodiorites of the Birandzhinskii massif, with which the gold mineralization of the Kutyn deposit in Khabarovsk krai is spatially connected, has been determined. Isotope–geochronological data show good convergence: the concordant U–Pb age of zircon is 90.7 ± 1.7 million years (SIMS), and the Rb–Sr age of the rock shaft and minerals is 92.7 ± 0.4 million years. Low εNd( t ) values (about –0.8) and high primary 87 Sr/ 86 Sr ratios (0.7051–0.7053) relative to the parameters of the depleted mantle suggest that granodiorites were formed with the participation of the continental crust. The formation of the Birandzhinskii massif coincides with the second stage of the development of the Khingan–Okhotsk volcano-plutonic belt. The Rb–Sr age of gold-bearing quartz–carbonate–sericite metasomatites of the Kutyn deposit is 79.3 ± 0.5 million years. The obtained isotope–geochronological data indicate a time gap (about 10–12 million years) between the crystallization of granodiorites and the formation of metasomatites, which suggests the allometasomatic nature of gold mineralization.

Iron and iron–manganese deposits form three closely spaced clusters within the Lesser Khingan Range of the Russian Far East. Fe-Mn mineralization is hosted in Vendian–Cambrian carbonates and composed of magnetite, hematite, braunite, haussmanite, rhodochrosite and pyrolusite. The iron–manganese ores are closely associated with explosive intermediate–felsic breccias, magnetite-rich lavas, dolerites and mineralized lithocrystalloclastic tuffs. Magmatic rocks display both concordant and discordant relationships with Fe-Mn mineralization and contain abundant xenoliths of host carbonates. Both magmatic rocks (with the exception of Nb-enriched dolerites) and Fe-Mn ores are characterized by variable enrichments in large-ion lithophile and light rare earth elements and strong depletions in high-field strength elements compatible with the broad subduction setting for explosive volcanism and associated hydrothermal Fe-Mn ore mineralization. Nd-Sr isotope systematics suggest contamination by both ancient and juvenile continental crust and the involvement of recycled pelagic sediment in the formation of Fe-Mn deposits in the Lesser Khingan Range of the Russian Far East.

DATA REPORT article Front. Earth Sci., 02 June 2023Sec. Petrology Volume 11 - 2023 | https://doi.org/10.3389/feart.2023.1156559

In tectonic history of many orogenic belts, alkaline granitoids with A-type affinity mainly reveal lithosphere extension events. However, precise dating of these rocks is often hampered by several problems either due to absence of accessory zircon or due to high U and Th contents disturbing the U-Pb isotope system. This study reports results of chemical abrasion isotope dilution-thermal ionization mass spectrometry (CA ID TIMS) U-Pb dating of zircon from five plutons of aegirine- and/or alkaline amphibolebearing alkali-feldspar granites and quartz syenites from the Trans-Altai Gobi (SW Mongolia) and Northern Mongolia in the Central Asian Orogenic Belt and reveals their close petrogenesis in different tectonic position. In the SW Mongolia the earliest Carboniferous alkaline granitoids (ca. 358-346 Ma) were formed during the post-accretion extensional event suggesting the Late Devonian accretion of the TransAlai Gobi-Eastern Junggar oceanic island arc to the Mongolian-Chinese Altai peri-Siberian continental margin. Alkaline granitoids of the Northern Mongolia were emplaced in the Early Permian during two independent geographically overlapping anorogenic near-coeval igneous pulses. The earliest pulse (ca. 285 Ma) related to evolution of the western half of the Northern Mongolia-Western Transbaikalia volcano-plutonic belt of alkaline granitoids with the bimodal volcanic sequences, is ascribed to the most significant Early Permian magmatic event throughout the Central Asian Orogenic Belt. The latest pluton (276 +/- 1 Ma) identifies the initial emplacement stage of the Middle Permian-Early Triassic Khangai granitoid batholith. Alkaline granitoids from the Trans-Altai Gobi and Northern Mongolia possess similar ferroan, mainly peralkaline, A(2)-type granite geochemical characteristics, but differ in Nd isotopic signatures. For the Trans-Altai Gobi plutons epsilon(Nd)(t) = +6.7; for Northern Mongolian plutons epsilon(Nd)(t) varies between -1.7 to + 0.6. These values are consistent with the Nd isotopic evolution of the continental crust of the hosting terranes, 'Hercynian' isotope province for the Trans-Altai Gobi and `Caledonian' province with a pre-Ediacaran microcontinent crust for the Northern Mongolia. Thereby studied alkaline granitoids were formed manly though anatexis of the host terrane crust during post-accretion and anorogenic extension events in different parts of the Central Asian Orogenic Belt. (C) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Continental rifting is usually viewed in terms of two contrasting models of active and passive extension. The origin of the Baikal Rift, adjacent to the southern part of the Siberian Craton, has been described by both models in the past. It is expected that basaltic magmatism in an active model scenario should be primarily sourced from a mantle plume or plume-fed asthenosphere, whereas melting of the lithospheric mantle is expected to be a predominant source for magmatism in the passive model. In this paper, we focus on the Miocene volcanic rocks sampled along two 60-km-long profiles that cross the boundary between the Neoproterozoic Tuva-Mongolian massif and the Archean-Paleoproterozoic Siberian Craton. Most of the samples studied are trachybasalts. In terms of trace element concentrations normalised to primitive mantle, the lavas mimic oceanic island basalt-like patterns with troughs at Rb, Th-U, Pb, and Y, and peaks at Ba, Nb, Ta, K, and Sr. Moreover, similar trace element patterns to the studied samples are also observed for Miocene and Quaternary lavas located in the southwestern of the Baikal Rift, and adjacent regions of non-rifted Mongolia. According to the ratio of CaO to MgO, and TiO2/Al2O3 to SiO2, the compositions of the studied lavas coincide with experimental melts derived from mafic lithologies. Trace element data of samples suggest that garnet was a residual phase during partial melting. The Sr-Nd isotopic characteristics of the studied lavas are Sr-87/Sr-86 0.70427-0.70469 and 1(43)Nd/Nd-144 0.51267-0.51284. They are identical to the coeval Miocene lavas of neighbouring volcanic fields, but they differ from the Quaternary lavas that extend to lower Sr-87/Sr-86 (0.7038-0.7044) with near identical Nd-143/Nd-144. Isotopes of Hf for studied samples show values epsilon Hf = 6.0-7.7, except for the two samples taken within the boundary between two lithospheric blocks with epsilon Hf 4.6 and 4.8. The delta O-18 of olivine from lava samples is everywhere higher than that of the asthenospheric mantle and ranges from 5.5 to 6.4 parts per thousand. Variations of delta O-18 versus Mg#, Sr-87/Sr-86 and epsilon Hf in the studied samples do not correlate, but do unequivocally rule out crustal assimilation. The isotopic variations are consistent with recycling of mafic crustal lithologies at mantle depths. Lavas from the Tuva-Mongolian massif and the Siberian Craton differ in lead isotopes by lower values of Pb-206/Pb-204 (< 17.785) and higher values of Delta 8/4Pb (61-75) for on-cratonic samples and the reverse relationship for off-cratonic lava (> 17.785 and 55-61), respectively. The equation for Delta 8/4Pb = [Pb-208/Pb-204-(1.209*(Pb-206/Pb-204) +15.627)] *100 is from Hart (Nature, 309, 753-757, 1984). The correlation of lead isotopes with the mafic recycled component, the sharp change of lead isotopic values at the cratonic boundary and decoupling of lead isotope ratios from other isotopic ratios lead us to suggest that the values of Pb-206/Pb-204 and Delta 8/4Pb are associated with an ancient accessory mineral phase such as sulphide confined within the lithospheric mantle. The predominant role of the lithospheric sources in the formation of the Miocene volcanic rocks indicate that the volcanism of the Baikal Rift was caused by a passive tectonic process, rather than active rifting.

The Eastern Mongolia volcanic area formed in the Late Mesozoic - Early Cenozoic within Central Asian Orogenic Belt. The main volcanic events of the area occurred in the Early Cretaceous when alkaline basaltic lavas erupted and formed the so-called cover volcanic complex. Geochemical and isotope features of the cover volcanic complex allowed researchers to identify the following mantle rocks as their source: metasomatized peridotites, eclogites, and pyroxenites. Thermodynamic modeling in alphaMELTS program was performed to determine whether the simultaneous melting of these rocks with subsequent processes of crystallization differentiation could lead to the formation of the studied rocks. The modeling results show that the melting of the most enriched with incompatible trace elements peridotites, eclogites, and pyroxenites cannot produce the rocks of the cover volcanic complex. At the same time, the mixing of peridotite- and eclogite-derived melts corresponds most closely to the mechanism of rock formation. However, Ti, K, P, Rb, and Sr enrichment of the studied rocks also requires participation in magma generation processes of mantle metasomatic veins enriched with rutile, apatite, phlogopite, and amphibole.