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This article considers the mineralogical and geochemical features of the Early Cretaceous gold ore deposits in the Northern Okhotsk region, that is, the southeastern flank of the Yana-Kolyma orogenic belt and the Okhotsk sector of the Okhotsk–Koryak orogenic belt. Dating results are reviewed and the general and distinctive geological, mineralogical, and geochemical features of different mineralization types are shown. A close genetic link of ore mineralization with Early Cretaceous magmatism and formation of the Uda-Murgal magmatic arc is assumed. [ABSTRACT FROM AUTHOR]

Data on the petrography, geochemistry, and isotopic geochronology of granites from the northern part of the Taimyr Peninsula are considered. The Early-Middle Carboniferous age of these rocks has been established (U-Pb, SIMS). Judging by the results of 40Ar/39Ar dating, the rocks underwent metamorphism in the Middle Permian. In geochemical and isotopic composition, the granitic rocks have much in common with evolved I-type granites. This makes it possible to specify a suprasubduction marginal continental formation setting. The existence of an active Carboniferous margin along the southern edge of the Kara Block (in presentday coordinates) corroborates the close relationship of the studied region with the continent of Baltia. [ABSTRACT FROM AUTHOR]

This paper presents new geochemical, U–Pb geochronological, and Sm–Nd isotopic data for early Paleozoic granitoids and acidic volcanic rocks within the Mamyn Terrane that constrain the early Paleozoic tectonic evolution of the eastern central Asian orogenic belt (CAOB). The Mamyn Terrane is usually considered part of the Argun Massif, although our new geochronological data indicate the presence of two magmatic events within the terrane that occurred at the Ediacaran–Cambrian boundary (∼541 Ma) and the late Cambrian–Early Ordovician boundary (507–488 Ma). Field observations indicate that all of the late Ediacaran–Early Cambrian (∼541 Ma) volcanic rocks are deformed whereas the Late Cambrian–Early Ordovician (507–488 Ma) intrusive and volcanic rocks are either deformed or undeformed. The ∼541 Ma magmatic event in the study area produced rhyodacite, trachyrhyodacite, and trachyrhyolite units that are either high-K calc-alkaline or shoshonitic. These units have ε Nd(t) values from −7.4 to −8.7, t Nd(DM) ages of 1.9–1.8 Ga, and formed from primary magmas generated by the partial melting of Mesoproterozoic continental crustal material in a suprasubduction zone setting. The Late Cambrian–Early Ordovician (507–488 Ma) magmatic event in this area formed gabbrodiorite, diorite, granodiorite, granite, trachyrhyodacite, and rhyodacite units that are medium-K and calc-alkaline, and have arc-like trace element compositions that are enriched in the large ion lithophile elements (LILEs) and depleted in the high field strength elements (HFSEs). These units have initial 87 Sr/ 86 Sr (i) ratios and ε Nd(t) values that range from 0.7048 to 0.7067 and from −3.3 to −0.2, respectively, yielding t Nd(DM) ages of 1.6–1.1 Ga. These features indicate that the magmas that formed these units were generated in a subduction zone setting, most likely by the partial melting of Mesoproterozoic crustal material with the addition of some younger juvenile material. In addition, the Late Cambrian–Early Ordovician trachyrhyodacite and rhyodacite units in this area are high-K and calc-alkaline or are shoshonitic and are enriched in K, Rb, the rare earth elements (REE), Y, Nb, Ta, and Zr, and are depleted in Sr and have A-type granite affinities. However, these units do not contain alkali amphibole or pyroxene and have high FeO tot /MgO ratios (6.7–12.7) that indicate they formed from highly fractionated magmas. Therefore, these volcanic rocks represent extreme melt differentiates that also formed the coeval granites. The early Paleozoic magmatic events within the Mamyn Terrane have also been identified in the Argun, Bureya, and Jiamusi areas of the eastern CAOB, suggesting that all of these areas have a common geodynamic history. [ABSTRACT FROM AUTHOR]

The article discusses the formation of large igneous provinces (LIP) in east Siberian craton and challenges associated with estimation of phanerozoic intraplate magmatism in the region. Topics discussed include basaltic magmatism, formation of magmatic rocks in early cretaceous High Arctic large igneous province (HALIP) in Siberia and petrogeochemical characteristics of the region.

The article discusses the study done on the tectonic setting, composition, and age of deeply metamorphosed rocks and the associated magmatic complexes in Svyatoi Nose Peninsula in Russia. Topics discussed include granulites providing reconstruction of geodynamic environments in the earth crust, representation of metamorphic rocks by alternating bands of basic gneiss and a triad of graphite marble, and quartzite-schist marble formation.

Abstract: The structure, composition, and age of Vendian–Early Cambrian plagiogranitoid associations composing the Kshta and Taraskyr massifs of the Yenisei pluton in the Altai–North Sayan island-arc belt are considered. We have established that these associations formed within 550–520 Ma and differ in petrographic composition and sources. Two stages of island-arc plagiogranitoid magmatism are recognized: early (550–540 Ma, formation of plagiogranitoids of the Kshta (545 ± 8 Ma) and Taraskyr (545 ± 7 Ma) massifs) and late (525–520 Ma, formation of plagiogranitoids of the Maina complex of the Yenisei (524 ± 2 Ma) and Tabat plutons). By petrochemical composition and geochemical characteristics, the rocks of the Kshta massif are high-alumina plagiogranitoids similar to adakites. They might have been produced through the melting of metabasites compositionally similar to N-MORB in equilibrium with garnet-containing restite during the subduction of oceanic slab at ≥15 kbar. The rocks of the Taraskyr massif are low-alumina plagiogranites. They formed through the melting of metabasites located in the lower layers and(or) the basement of the island-arc system in equilibrium with plagioclase-containing restite at 3–8 kbar. The low-alumina plagiogranitoids of the Yenisei pluton melted out under the same conditions. Isotope-geochemical studies showed that the Vendian–Early Cambrian plagiogranitoids formed at the early stage are characterized by high positive ∑Nd(T) values (7.5–4.9), Late Riphean model Nd-age (TNd(DM) = 0.64–0.98 Ga), and Sr isotope ratio varying from 0.7040 to 0.7053. These data point to the juvenile parental melts of the rocks and the varying content of ancient crustal material in the magma generation zone. [Copyright &y& Elsevier]

Abstract: The formation and evolution conditions for alkaline magmatism and associated igneous rocks in the western framing of the Siberian craton are shown by the example of alkaline and subalkaline intrusive bodies of the Yenisei Ridge. Here we present petrographic, mineralogical, geochemical, and geochronological data for the rocks of the Srednetatarka and Yagodka plutons located within the Tatarka–Ishimba suture zone. Ferroan and metaluminous varieties enriched with rare elements (Nb, Ta, Zr, Hf, and REE) are making up most of the studied rocks. They formed at the stages of fractional crystallization of alkaline magma in a setting of active continental margin in the west of the Siberian craton in the Late Neoproterozoic (710–690 Ma). As differentiates of mantle magmas, these rocks associate with Nb-enriched rocks—A-type leucogranites and carbonatites. Sm/Nd and Rb/Sr isotopic data imply a predominance of the mantle component in the magmatic sources of the mafic and intermediate rocks as well as contamination processes of various volumes of continental crustal material by this magma. [Copyright &y& Elsevier]

The article discusses late mesozoic adakite volcanism of the Ugan volcanic structure in the southeastern margin of the North Asian Craton. It focuses on the geochronological and geochemical evidences of argon isotopes dating. It adds that the eastern margin of the Asian continent is characterized by wide development of late Mesozoic magmatic processes. It further explores that these processes take place as a result of formation of spacious fields and extended belts of volcanic and plutonic rocks. It also presents geodynamic settings of these processes. It discusses volcanic fields superimposition on structures of various ages of the Dzhugdzhur-Stanovoi superterrane in Russia.

Abstract: The studied massifs in Western Transbaikalia (Arsentyev and Orongoi) are composed of pyroxenites, high-Ti subalkalic gabbro, gabbro-diorites, monzodiorites, anorthosites, and syenites. The Orongoi massif also includes small olivinite and plagioperidotite bodies. The gabbroids have high contents of Sr, Ba, Nb, Ta, Zr, and Hf, which is typical of intraplate basites. The REE pattern shows the rock enrichment in LREE (La/YbN = 5.35–25.82). The 87Sr/86Sr values vary from 0.7050 to 0.7054, and εNd, from 1.44 to –1.18. The presence of radiogenic Nd in the gabbroids and their enrichment in 87Sr suggest their formation as a result of the melting of the EM-II-type lithospheric mantle. [Copyright &y& Elsevier]

Abstract: This paper presents the results of the first comprehensive geological, petrographic, mineralogical, geochemical, and geochronological studies of ultramafic and mafic magmatism in the poorly explored southwestern Tuva (evidence from the Birdag and Khayalyg massifs). These massifs intrude ortho- and paraschists, which are presumably Middle Proterozoic. Amphibole gabbros in the Khayalyg massifs contain numerous relict host-rock xenoliths. The massifs are dominated by meso- and leucocratic amphibole gabbros with minor ultramafic (serpentinous plagioclase harzburgites and plagioclase lherzolites) and transitional (wehrlites, olivine clinopyroxenites, hornblendites, melanocratic olivine gabbronorites) rocks. The serpentinous plagioclase harzburgites and plagioclase lherzolites occur in the amphibole gabbros of the Birdag massif as small lenticular bodies. The latter are interpreted as xenoliths of ultramafic restites of earlier protrusion rather than mafic-melt differentiates. The wehrlites, olivine clinopyroxenites, hornblendites, and melanocratic olivine gabbronorites forming the outer zones of the xenogenic bodies of ultramafic restites are considered hybrid rocks. They resulted from the contact reactions of mafic melts and their fluids with the xenogenic bodies of ultramafic restites, which were feldspathized during this interaction. In the gabbros from both massifs, the chondrite-normalized content of MREE and HREE is lower and that of LREE is higher than those in N-MORB. The plagioclase peridotites, wehrlites, and olivine clinopyroxenites forming xenogenic bodies among the amphibole gabbros of the Birdag massif are richer in REE (especially LREE) than the ultramafic restites in ophiolite associations. This is because they were infiltrated by fluids enriched in these elements during their alteration under the influence of later mafic melts. The studies suggest that the Birdag and Khayalyg ultramafic–mafic massifs result from the spatial coexistence of (1) more ancient small protrusions of ultramafic restites, which occurred as allochthons among Middle Proterozoic(?) metamorphic rocks, (2) later gabbroic intrusions (from 494 ± 16 to 450–447.4 ± 5 Ma), and (3) hybrid transitional rocks (wehrlites, olivine clinopyroxenites, hornblendites, melanocratic olivine gabbros) making up contact-reaction zones along their boundaries. [Copyright &y& Elsevier]

This article presents the data of studies of ion-salt, microcomponent, gas, and isotopic compositions of water and the equilibrium calculation results for the water-rock system. The Tersinskie carbonic-acid waters are shown to be genetically close to soda waters of the Kuznetsk Basin (Kuzbass) in the zone with slowed water exchange. Taking these data into account, the concept of formation of carbonic-acid mineral waters not connected with magmatic or volcanic activities in the region was developed. According to this hypothesis, carbonic-acid waters are soda waters of regional occurrence, their composition being considerably changed due to CO introduction from the deeper zones of the Earth's crust along the zones of tectonic ruptures. [ABSTRACT FROM AUTHOR]

The article presents a study which aims to determine the depth of formation of primary basalt magmas under different volcanic fields in the Baikal Rift System based on chemical composition of volcanic products. It notes on the gravimetrical data that the value of the extension in the rift increases linearly from the pole towards the South Baikal depression and elaborates on the fact that crustal extension is compensated by magma intrusion. Moreover, the study also considers the inflow of deep mantle matter in generation of basalt magmas.

The article presents a study which aims to determine the role of samarium-neodymium (Sm-Nd) isotope constraints on granitoid magmatism and hydrous metamorphism in the history of the uralian platinum belt. It notes on the inclusion of two manifested geological epochs or date of reference of the tectonic-metamorphic development of the belt. An illustration is presented which depicts granitoid magmatism and hydrous metamorphism that show the scheme of the geological structure of the Denezhkin Kamen formation. Moreover, the new isotope data has suggested that tectonic extension is almost synchronous within the Platinum Belt.

Abstract: The Kuznetsk Basin is located in the northern part of the Altai–Sayan Folded Area (ASFA), southwestern Siberia. Its Late Permian–Middle Triassic section includes basaltic stratum-like bodies, sills, formed at 250–248 Ma. The basalts are medium-high-Ti tholeiites enriched in La. Compositionally they are close to the Early Triassic basalts of the Syverma Formation in the Siberian Flood basalt large igneous province, basalts of the Urengoi Rift in the West Siberian Basin and to the Triassic basalts of the North-Mongolian rift system. The basalts probably formed in relation to mantle plume activity: they are enriched in light rare-earth elements (LREE; La n = 90–115, La/Sm n = 2.4–2.6) but relatively depleted in Nb (Nb/LaPM = 0.34–0.48). Low to medium differentiation of heavy rare-earth elements (HREE; Gd/Yb n = 1.4–1.7) suggests a spinel facies mantle source for basaltic melts. Our obtained data on the composition and age of the Kuznetsk basalts support the previous idea about their genetic and structural links with the Permian–Triassic continental flood basalts of the Siberian Platform (Siberian Traps) possibly related to the activity of the Siberian superplume which peaked at 252–248 Ma. The abruptly changing thickness of the Kuznetsk Late Permian–Middle Triassic units suggests their formation within an extensional regime similar to the exposed rifts of Southern Urals and northern Mongolia and buried rifts of the West Siberian Basin. [Copyright &y& Elsevier]

Abstract: Complex petrological, geochemical, and isotope studies of igneous rocks sampled from the core of parametric Maizasskaya BH-1 showed a predominance of dolerite sills, which formed earlier (~263 ± 4 Ma) than most of basalts in the basement of the West Siberian sedimentary basin and in the Siberian Platform traps (248–251 Ma). Their formation took place during the crystallization of basaltic melt in intrusive chambers existing between layers of Silurian sedimentary rocks. The petrochemical, geochemical, mineralogical, and thermobarogeochemical data show that the sills resulted from the activity of complex magmatic systems different from typical oceanic and plateau-basalt melts and related, most likely, to the formation of rift structures under the influence of mantle plume. Study of melt inclusions provided data on the conditions of generation of primary melts from mantle substratum (≤1570 ºC, depths to 105–120 km) and crystallization parameters of dolerites—1130–1155 ºC, 1.5–2 kbar. The results obtained show that the studied basalt complexes in West Siberia are genetically related to the mantle plume activity, which led to the breakup of ancient crust and rifting. Formation of oceanic crust took place in the largest rifts; the ascending magma penetrated into the enclosing ancient strata to form sills. [Copyright &y& Elsevier]

Abstract: In this paper we present complex geological, petrographic and geochronological data of the study of intermediate and acid composition intrusive and volcanogenic rocks from the Porozhnaya massif of the South Yenisei Ridge. For the first time in the Yenisei Ridge Devonian and Triassic U-Pb age values (SHRIMP method) have been obtained for leucogranites—387±5 Ma and alkaline trachytes—240±3 Ma, which allows us to attribute them to two different complexes, despite the fact that these rocks were formed within the same Severnaya riftogenic structure. Geochronological Ar-Ar data (392–387 Ma) for micas from paragneisses and leucogranitic dikes of the Yenisei suture zone on whose extension the Severnaya riftogenic structure is located are also given in this study. These data on Devonian tectonic-magmatic events in the South Yenisei Ridge agree well with coeval events of continental rifting—the formation of intrusive and volcanogenic rocks of the Agul graben in the Prisayan region and the Minusa basin in the Altai-Sayan folded area. The forming of alkaline trachytes and alkaline syenites of the Severnaya riftogenic structure, for which an age of 240±3 Ma has been established, is related to the trap magmatism of the Siberian platform. [Copyright &y& Elsevier]

The article presents an analysis of Paleozoic tholeiite magmatism manifestation in the Kola alkaline province in northeastern Fennoscandia. It states that the manifestations are presented by dolerite dikes composed of swarms such as Pechenga, the Barents Sea, and East Kola. Potassium-Argon (K—Ar) dating shows that the estimated age of Pechenga swarm ranges from 355-600 million years, which is the same with the Barents Sea swarm. The Pechenga Swarm has 1-8% olivine-normative and quartz-normative of 1-3% while rocks found in Barents Sea and East Kola contains normative-quartz of 1-10%. It concludes that the partial melting of mantle substrate in the spinel lherzholite facies is associated with tholeiites that matched to the initial stage of plume-lithosphere interaction.

Abstract: Isotope dating of ultrapotassic magmatism in the central Chukchi region was carried out. Based on the Rb-Sr isochron age of monzonites from the Linkor stock (107±2.2. Ma) and using earlier obtained geochronological isotope data, we have estimated the time of one of the stages of ultrapotassic magmatism, 107–113 Ma. Igneous rocks of this age occur throughout the central Chikchi region, which suggests their genetic relationship with some great geodynamic event there, likely, the accretion of the Mainit island arc to the Chukchi microcontinent. The results obtained permit the reconstruction of the geologic history of the region and can be used to construct more detailed geodynamic models. [Copyright &y& Elsevier]

The article presents a multireservoir thermodynamic model of the formation of the Sukhoi Log gold mines in Irkutsk Oblast, Russia. Topics discussed include the formation of the ore in the mine due to metamorphic–metasomatic and magmatic–hydrothermal procedures, granitoid magmatism and formation of gold deposits under the influence of metal bearing fluids.

New U-Pb geochronology and a large and growing geochemical data base has clarified the age and composition of the extensive magmatic belts of NE Russia, allowing a better understanding of their relation to the plate tectonic evolution of the circum- Pacific margins of Russia, Alaska and the North American Cordillera, as well as to plate tectonic events that formed the Arctic Ocean. Prior to the magmatism described here, the paleo-Pacific margin of Siberia (now the Verkhoyansk-Kolyma orogen), Arctic Chukotka and the Brooks Range, Alaska, shared passive margin sedimentation from the Triassic to mid-Jurassic. Deformation along this once contiguous margin began with closure of deep-water basins and culminated with emplacement of oceanic and arc rocks onto the margin with continuing shortening of the margin into the Jura-Cretaceous. The Main Kolyma batholith belt (calc-alkaline granites to granodiorites) (158-144 Ma, peak 150±3 Ma) and the paired Uyandina-Yasachnaya volcanic arc are thought to have resulted from west-dipping subduction. Northern belt plutons (calc-alkaline) are 140-129 Ma and mostly post-date the E-W trending oroclinal bend of the northernVerkhoyansk fold belt. Calc-alkaline granites to granodiorites spanning 125-100 Ma intruded across Chukotka (Artic Russia) and Alaska during extension, right lateral shear and subduction zone retreat towards the Pacific perhaps coeval with the onset of rifting in the Amerasia Basin of the Arctic. The Uda-Murgal arc evolved independently along the Taigonos and Okhotsk part of the Russian margin, between 150-130 Ma and 107-97 Ma, and was followed by the establishment of the margin-parallel Okhotsk-Chukotka volcanic belt (OCVB), erupted in a neutral to slightly extensional tectonic regime, beginning 106 Ma, but, mostly between 98-80 Ma and ending ~ 76 Ma. Age equivalent magmatism in the Bering Strait is associated with continued extension, melting and remobilization of the deep crust. Between 80-60 Ma, subduction-related magmatism stepped south to the outer Bering Shelf and then to the Aleutians before 46 Ma. A similar process occurred in Russia with the pre-55 Ma onset of opening of the Sea of Okhotsk and step-wise migration of the subduction zone to eastern Kamchatka and Kuril Islands. These events broadly coincide with the opening of the Eurasia Basin of the Arctic. Profound differences occur in the tectonic setting of magmatism through time along strike of the subducting margin from Russia to the North American Cordillera. From 125 to 60 Ma, the NE Russian and Alaskan sectors of the margin underwent mostly neutral to extensional tectonism while the Cordillera underwent crustal shortening. Although vast amounts of paleo-Pacific oceanic lithosphere were subducted beneath both sectors of the margin, it appears that in a mantle reference frame, the Cordillera moved mostly towards its subduction zone while the overriding continental plates in NE Russia and Alaska moved parallel to or away from their subduction zones, allowing magmatism to take place in tectonically neutral or extensional settings. The coupled timing of trench-towards versus trench-away events related to motion of the overriding plates led to the observed "dance" of magmatism and deformation along the northern circum-Pacific margin. • U-Pb geochronology, geochemistry, tectonic setting of Mesozoic magmatism, NE Russia. • Subduction is shared but tectonic style differs from NE Russia to the Cordillera. • Dance of magmatism and deformation is linked to absolute motion of continental plates. [ABSTRACT FROM AUTHOR]

The age of Franz Josef Land (FJL) basalts is the topic of discussion in modern geology. There are two main points of view to the question. The 1st is short-term one-stage formation of a large eruptive province (LIP) at the beginning of the Cretaceous, based on geology, stratigraphy and some U-Pb dates. The 2nd is a long-lived (from the beginning of the Jurassic on the early Cretaceous) a hot spot with several brief pulses of magmatic activation. It is connected with Ar-Ar dates, which allows us to distinguish three stages of magmatism (196 – 186 Ma, 160—153 Ma and 145—125 Ma.More than 50 samples of FJL basalts were studied. Petrochemical, geochemical, radiological data were obtained. According to the material characteristics the basalts are tholeiitic, with geochemical features of intraplate origin. Paleomagnetic data shows the Age was investigated in 12 samples by the Ar-Ar method in plagioclase and pyroxene monofractions. In 11 samples, the age corresponds to the interval from 125 to 145 Ma. By comparison on a one scale they line up into a single continuous episode of active volcanism. In the 12th sample, two equal-sized plateaus are clearly distinguished, corresponding to the age of 130 Ma (45%) and 186 Ma (40%).Such specific Ar-Ar spectra are in evidence in other hypabyssal formations in the intraplate conditions. For example, some lamprophyres of chuya complex (SE Altai-NW Mongolia) show the same characteristics (276 Ma (30%) and 258 Ma (40%) for the one rock).As a result of our investigation we suggest that the basalts of FJL were formed at one episode of intraplate magmatism. Dates 186-196 Ma reflect the intratelluric stage of phenocrysts forming. And the interval 125-145 Ma corresponds to the crystallization of the whole rock.This work was supported by the RFBR (projects No. 18-35-00273, 18-05-70035); The Ministry of Education and Science of the Russian Federation (projects 5.2324.2017 / 4.6 and 5.4786.2017 / 6.7), project №0330-2016-0002 [ABSTRACT FROM AUTHOR]