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The studies are focused in the Mara–Kamenka–Uvat interfluve of the Biryusa Uplift of the basement of the Siberian Platform, where the Mara paleovolcano was recognized during the prospecting works for manganese more than 50 years ago. The specific volcano-sedimentary rocks are considered in the structure of the Late Riphean Karagas Group. Our mineralogical and petrographic studies allowed us to establish abundant high-K pyroclastic rocks, ignimbrites, and trachybasalts, which indicate a subaerial explosive character of the Mara volcano. The age of high-K volcanism of 640 Ma is based on U–Th–Pb dating of zircon. The Lu–Hf isotope systematics of zircon indicates a link of volcanism with mantle magmas. The composition and the period of the formation of rocks prevent their correlation (as was considered before) with sedimentary Late Riphean quartz and quartz–feldspar sandstones of the Karagas Group and dolerites of the Nersa intrusive complex. Specific mineralogical–petrographic features of rocks allow their use as a regional stratigraphic reference. [ABSTRACT FROM AUTHOR]

The Sr-isotopic composition in carbonate rocks aged 980–920 Ma has been defined in only one place in the world, the Huainan Formation of the North China Platform, with the accumulation time limited by U–Pb data of detrital zircon grains. The upper part of the Nizhny Tunguska Formation in the Turukhansk uplift is found to contain altered volcanic rocks, as well as weathering crust products along them, such as poor bauxite and chamosite ores, among carbonate deposits. Based on U–Pb zircon isotope dating, the age of the volcanic rocks is 963 Ma. For the least altered limestones in the upper part of the Nizhny Tunguska Formation, the 87Sr/86Sr values were obtained equal to 0.70532–0.70578, which are close to those found in the rocks of the Huainan Formation. These data about the geochronological age of the studied limestones make it possible to obtain more accurate data, which allows refining the previously proposed configuration of the Sr-isotopic composition variation curve in the Early Neoproterozoic. The Nizhny Tunguska Formation compares favorably with the Huainan Formation in being the world's only Early Neoproterozoic carbonate sequence that is correctly geochronologically substantiated (based on zircon from subsynchronous volcanic rocks). [ABSTRACT FROM AUTHOR]

The new species Icriodus alchedatensis sp. nov., I. kuzbassiensis sp. nov., I. lebedyankensis sp. nov. and Latericriodus sp. E are described from stratotype sections of the Mazalovy Kitatian Regional Substage (Middle Givetian) from the Kolyvan-Tom folded area. The taxa of the genus Icriodus belong to two lineages within the genus Icriodus the I. struvei lineage and the I. regularicrescens lineage according to the Weddige's (1977) concept. [ABSTRACT FROM AUTHOR]

The Chadobets alkaline-carbonatite complex (Siberian craton) is a natural laboratory for all varieties of ultramafic lamprophyres, including damtjernites formed by fluid-explosion mechanisms, which contain a large number of pelletal lapilli. Data obtained from comprehensive mineralogical, structural and chemical studies of these pelletal lapilli show strong similarity with the main magmatic mineral assemblage of damtjernites, suggesting a juvenile composition for them. The composition of phlogopite, carbonate and fluorapatite in pelletal lapilli is mostly constrained toward primitive compositions (beginning) of mineral crystallization trends in ultramafic lamprophyres. According to the petrographic and mineralogical features found in pelletal lapilli from damtjernites, these can be divided into three types based on the conditions and depth of formation. Estimated late magmatic temperatures of pelletal lapilli mica and fluorapatite formation vary from 815 to 990 °C. [ABSTRACT FROM AUTHOR]

The chemical composition of alkaline (Late Cretaceous basanite) and subalkaline (Permian–Triassic dolerite) basaltoids of different ages in the northern part of the Minusa Trough was studied by optical emission spectroscopy and mass spectrometry with inductively coupled plasma. The revealed differences of subvolcanic rocks in the nature of enrichment in HFS- and LIL-elements may indicate the generation of primary magmas at different depths and small degrees of melting of garnet and spinel mantle peridotite. The model of decompression partial melting of the subcontinental lithospheric mantle under the garnet stability conditions is applicable to the formation of basanite. It is assumed that the formation of dolerite magma was due to the interaction of the melt from shallower spinel peridotite with the "OIB component" of the sublithospheric mantle plume. [ABSTRACT FROM AUTHOR]

The paper summarizes major and trace-element compositions and Sm–Nd isotope data on metabasites (amphibolites) and gabbroids of the Onot granite–greenstone block in the Sharyzhalgai basement uplift, southwestern Siberian craton. The Onot block consists of tectonically combined nappes of the Paleoarchean tonalite–trondhjemite–granodiorite (TTG) complex and the metasedimentary-volcanic complex of the greenstone belt (GB). The Mezoarchean (∼2.88 Ga) metabasalts of the greenstone belt and Paleoproterozoic (∼1.86 Ga) gabbronorites and vein gabbros were formed at rifting and postcollisional extension, respectively. The Archean metabasites of the greenstone belt and enclaves in the TTG complex compositionally correspond to low-Ti tholeiitic basalts and basaltic andesites. The basaltic rocks are characterized by flat REE patterns [(La/Sm)n = 0.9–1.9], depletion in Nb relative to Th and La (Nb/Nb* = 0.4–1.1), and a wide range of mostly positive εNd(T) values (from +5.2 to –1.0). The enrichment of the basaltic andesite in incompatible elements, its Eu minimum, and negative εNd(T) values resulted from contamination by Paleoarchean TTG gneisses, that form the basement of GB. The Paleoproterozoic gabbronorites have high Mg# and extremely low concentrations of Ti and incompatible elements. The rocks are characterized by low (Nb/Y)PМ (0.8–1.0), negative εNd(T) values (from 0 to –1.4), and weak enrichment in Th and LREE relative to Nb. The vein gabbros have low (La/Sm)n, positive εNd(T) values of +2.8 and +0.3, and a negative Nb anomaly (Nb/Nb* = 0.3–0.4). The trace element-composition of the amphibolites, gabbronorites, and gabbros and the results of geochemical modeling indicate that the parental melts were derived mainly from weakly depleted mantle sources. The Nd isotope composition of the Paleoproterozoic gabbroids resulted from the evolution of the heterogeneous Archean lithospheric mantle. Variations in the isotope and trace-element composition of the amphibolites reflect the initially depleted nature of the Mezoarchean mantle and its metasomatic alteration by fluids/melts, which occurred before its melting at ∼2.88 Ga. The geochemical and Nd isotopic characteristics of gabbronorites and gabbros indicate that the lithospheric mantle had become progressively more heterogeneous by the Paleoproterozoic due to preceding Archean processes. The variable depletion of both the Archean and the Paleoproterozoic mafic rocks in Nb relative to Th and La may be explained by mantle metasomatism and does not reflect the geodynamic settings of the mafic magmatism. [ABSTRACT FROM AUTHOR]

In this study, we discuss mineral chemistry data, melt inclusion study results, and report Ar–Ar phlogopite age for the aillikite dikes of the Arbarastakh alkaline-carbonatite complex on the Aldan-Stanovoy shield, Russia. Aillikite was crystallized at 631 ± 8.5 Ma, coeval with the intrusion age of the Arbarastakh rocks. The Arbarastakh complex was formed during the late Neoproterozoic epoch of rare earth element-Nb ore-bearing alkaline-carbonatite magmatic activity that was widespread on the southwestern and southern margins of the Siberian craton, related to rifting processes during the breakup of the supercontinent Rodinia. The aillikites show mineralogical characteristics of primitive magmas such as highly forsteritic olivine, Mg-ilmenite, and Cr-rich spinel. The variance in olivine zonation, morphologies, and chemical element distribution indicate that olivine in the aillikites is represented by several genetic types: xenogenic olivines (Fe-poor cores) from the sheared peridotite, olivine antecrysts (Fe-rich cores) related to mantle metasomatism by preceding proto-aillikite melt, and olivine phenocrysts formed during crystallization of aillikite melt. The latter shows decreasing Ni and Cr due to fractional crystallization of olivine, ilmenite, and chromite, along with increasing Mn and Ca concentrations that are consistent with enrichment of these elements in the residual melt. The olivine phenocrysts chemistry shows variations that are characteristic of the presence of phlogopite and carbonate in the mantle source (low 100*Ca/Fe (0.4–1.2) and 100*Mn/Fe (1–2), moderate 100*Ni/Mg (1.4–0.4)). Spinel shows a wide compositional variation with two compositional zoning trends, one of which follows the titanomagnetite trend, while the other follows the qandilite-rich magnesio-ulvöspinel-magnetite one. The latter trend indicates an increase in f O2 and attendant Fe oxidation to Fe3+ during crystallization. Ilmenite composition evolution (from Mg-rich to Mn-rich) also reflects the carbonate-rich nature of aillikite melt. We identify primary melt inclusions hosted in phlogopite and secondary melt inclusions in olivine; both melt inclusions types have daughter minerals dominated by dolomite, calcite, Na-Ca carbonates, phosphates, and phlogopite, consistent with the carbonate-rich nature of aillikite melt. The calculated temperatures reflect the early stage of aillikite crystallization, with values ranging from 1169 to 1296°C and f O2 values (olivine-spinel pair) varying from +0.40 to +1.03 ΔFMQ and from ΔNNO −0.9 to ΔNNO −2.0 (perovskite oxygen barometer); in contrast, the homogenization temperature of the secondary melt inclusions in olivine (700–720°C) characterizes late-stage aillikite melt evolution. The carbonate-rich nature of the Arbarastakh aillikite and its similar age to the carbonatites are consistent with a genetic relationship between them. [ABSTRACT FROM AUTHOR]

The Agronomic Revolution implies a gradual sophistication of organism-substrate interactions and progressive colonization of shelf environments by vagile endobenthos in the late Ediacaran and Cambrian periods. These changes are impressively mirrored in a palaeontological record of ichnoassemblages in marine siliciclastic facies. In contrast, endobenthic communities in carbonate successions remained comparatively poor until a fundamental transformation during the Great Ordovician Biodiversification Event. Herein we report complex open burrows (Thalassinoides and Olenichnus) from the Sukharikha Formation exposed near the Plakhinskii Island (Yenisei River, Igarka Uplift). Lithological and chemostratigraphical correlation with the stratotype suggest the Terreneuvian age of the fossil-bearing strata accumulated in storm-agitated mid- to distal inner-ramp settings. Each of the ichnotaxa occurs in a specific deposit in the studied section: Olenichnus is localised exclusively in the background-sedimentation deposits, whereas Thalassinoides occurs in the storm-event beds. Our data support early reports suggesting that colonization of marine carbonate sediments by burrowing metazoans was initiated already in the Terreneuvian and became a solid basis for the following development of deep-tier bioturbation in carbonates in the Ordovician Period. [ABSTRACT FROM AUTHOR]

New species Belodella salairica sp. nov. and Caudicriodus yolkini sp. nov. are described from stratotype sections of the Middle Devonian Mamontovian and Zarechnian regional substages of the northeastern slope of Salair. [ABSTRACT FROM AUTHOR]

The biostratigraphic data on the ammonoid, brachiopod, conodont, and ostracod assemblages of the Mamontovo and Zarechnoe horizons of the Salair were revised and analyzed. The stratigraphic succession of the Middle Devonian deposits of the Salair is clarified, and the new Zarechnoe Horizon, including the Akarachkino, Safonovo, and Kerlegesh beds, is proposed. The upper Eifelian ammonoid assemblage of the Agoniatites Zone, established in the upper part of the Akarachkino Beds, is the biostratigraphic level for global correlations. The upper Eifelian and lower Givetian brachiopod assemblage (Indospirifer padaukpinensis (=I. pseudowilliamsi)) characterizes the Safonovo Beds. Two middle Givetian brachiopod zones were recognized in the Kerlegesh Beds: Rhynchospirifer hians (=Ilmenia subhians) and Subrensselandia? salairica (="Chascothyris" salairica). The conodont assemblage of the Akarachkino Beds characterizes the upper Eifelian. The middle Givetian conodont assemblage, including Icriodus difficilis Ziegler et Klapper, Polygnathus linguiformisklapperi Clausen, Leuteritz et Ziegler, Po. parawebbi Chatterton beta morphotype, Po. ovatinodosus Ziegler et Klapper, and Po. pseudofoliatus Wittekind, was found in the upper part of the Safonovo Beds. No conodont assemblage was found in the Kerlegesh Beds. [ABSTRACT FROM AUTHOR]

The paper summarizes major, trace, and Sm-Nd isotopic data on metabasites of the Urik greenstone belt (GB) (Sharyzhalgai uplift, southwestern Siberian craton). The Archean metabasalts (amphibolites and garnet amphibolites) of the supracrustal complex and sheeted bodies represent four geochemical types. The first type includes low-Ti amphibolites of the Urik area. Their characteristic features are a clear LREE depletion ((La/Sm)n = 0.8–1.1), the absent negative Nb anomaly, and positive εNd(t) values (up to +4.1). The second type corresponds to moderate-Ti amphibolites of the Urik area. They differ from the rocks of the first type in the higher (La/Sm)n ratio (1.0–1.5), Th, Zr, Nb, Y contents, and lower εNd(t) values (+0.4...–1.6), but, like the low-Ti amphibolites, they do not show Nb depletion. The third type includes amphibolites of the Tagna area, which show an increase in the concentrations of TiO2, LREE, Th, Zr, and Nb with a decrease in Mg# and have εNd(t) values from +1.3 to –0.5. They are characterized by the elevated (La/Sm)n ratio (1.1–2.3) and Zr and Nb contents and the presence of a clear Nb minimum. The fourth type includes all high-Ti amphibolites of sheeted bodies, which are enriched in LREE ((La/Sm)n = 1.9–3.4), Th, Zr, and Nb, have an increased (Gd/Yb)n (1.4–2.0), a sharp Nb depletion, and negative εNd(t) values. Geochemical modeling coupled with trace element and isotopic composition indicates the formation of the low- and moderate-Ti metabasalts of the Urik area from weakly depleted and nearly primitive mantle sources, respectively. Their protoliths were oceanic basalts. The metabasalts of the Tagna area were formed from a weakly depleted and hydrated mantle source contaminated with crustal material. The enrichment of the source with incompatible elements could be caused by sediment subduction shortly before basalt formation. The metabasalts of the fourth type originated from a long-lived enriched source such as subcontinental lithospheric mantle. They resemble the present-day intraplate continental basalts. None of the three dominant types of metabasalts of the Urik GB shows signatures of sharply depleted or sharply enriched mantle sources, which indicates a weak differentiation of the mantle by the Meso- Neoarchean boundary (~2.8 Ga). The formation of a subduction-modifed lithospheric mantle (hydrated mantle) has only occurred since ~ 2.8 Ga. Different compositional and isotopic characteristics of the metabasalts of the Urik GB suggest that the Bulun terrane was formed by accretion and tectonic juxtaposition of fragments of the oceanic crust, an oceanic island arc, and an older TTG continental crust at ~ 1.86 –1.82 Ga. [ABSTRACT FROM AUTHOR]

On the basis of petrographic and mineralogical studies, we have established the presence of clastic rocks with a strong predominance of K-feldspar among the rock-forming fragments within the Late Precambrian sedimentary sequence in the southwestern part of the Siberian Platform. Two types of mineralogical occurrence of K-feldspars are determined: (1) huge zonal crystal clasts with increased Ba concentrations in the central parts of the grains and (2) the main mineral phase in the form of a decrystallized glassy mass. In both cases, low concentrations of Na (lower than 0.1 wt %) are detected. K-feldspars of the second type contain intergrowths of idiomorphic rhombic dolomite with a high ankerite component. Dolomite grains contain inclusions of K-feldspar. The prevailing accessory minerals are F-apatite (with high concentrations of REEs), zircon (with high concentrations of Th), magnetite, rutile, monacite, and sinchizite. Encasement minerals with an idiomorphic shape are identified, with K-feldspar being located in the center, while the middle shell is formed by apatite with a high REE content, and the outer shell is formed by apatite without rare earth elements. These rocks are products of high-potassium volcanic activity. The age of this event has been established on the basis of U–Pb zircon dating to about 640 Ma. The Lu–Hf zircon systematics for these rocks indicates the connection of volcanism with igneous events of mantle genesis within its range. The products of explosive eruption, which are widespread within the Biryusa uplift of the Siberian Platform, were erroneously considered earlier as Riphean sedimentary rocks of the Karagas Series. [ABSTRACT FROM AUTHOR]

For the first time, a thermomechanical model of a system of multilevel magma chambers above a mantle heat source has been developed to explain the formation mechanisms of intrusive complexes and metamorphic aureoles in Western Sangilen. A model of "thermal blur" at the collision stage and a model of a local magma reservoir at the transtension stage are proposed. The magmatic process was studied using a numerical thermomechanical model of the system magma reservoir–magma transport–formation of intermediate chambers–formation of metamorphic zonal complexes around intrusions at different depth levels. Modeling explains the mosaic distribution of granulite metamorphism zones in the Sangilen block. Model estimates of the duration of intrusive processes were obtained. The change in tectonic regimes in the evolution of Western Sangilen affects the depth of emplacement of gabbro–monzodiorite massifs and surrounding metamorphic aureoles. [ABSTRACT FROM AUTHOR]

Data on the carbon and oxygen isotopic composition of carbonates from the rocks of the Giyani greenstone belt, Kaapvaal craton, South Africa are presented. This belt is immediately adjacent to the Hout River Shear Zone, along which the Southern Marginal Zone (SMZ) of the Limpopo granulite complex is overthrusted onto the Kaapvaal craton. The δ13C values are –2.1 and –2.2‰ for carbonates from two metapelite samples, –5.1‰ for a meta ultrabasite sample, and –7.1 and –7.7‰ for two metabasite samples, respectively. The δ18О values are 17.1 and 17.5‰ for carbonates from the metapelites, 14.3‰ for carbonates from the metaultrabasite, and 12.9 and 13.0‰ for carbonates from the metabasites. The comparison of the data obtained to the published data on the isotopic composition of carbonates from the rocks of the different greenstone belts indicates both hydrothermal (in the metabasites and the metaultrabasite) and sedimentary (in the metapelites) origins of the carbonate material in the rocks studied. Based on the comparison of these data to δ13C of magnesite that formed in ultrabasic granulites during the interaction of the Limpopo complex with the craton, the graphite and fluid inclusions in leucocratic garnet-bearing granitoids that transported fluids, and the carbon isotopic composition of graphite from metapelites of the SMZ, it is concluded that the carbon source was located outside the SMZ and represented a heterogeneous carbonate-bearing lithologies. It could be carbonate-bearing volcanogenic–sedimentary sequences of the greenstone belts of the Kaapvaal craton, which underwent prograde metamorphism during the interaction with the SMZ granulites. [ABSTRACT FROM AUTHOR]

Late Devonian conodonts, recovered from the siliceous and carbonate rocks of the upper part of the Akbasay Formation on the left side of the Kule Gorge, Zeravshan-Gissar mountainous area (Uzbekistan), are studied. Seven conodont associations are defined for the Frasnian–Famennian interval. [ABSTRACT FROM AUTHOR]

The mineral composition, petrography, and petrochemistry of middle Cambrian diopside porphyry basalts of the Ust'-Sema Formation in Gorny Altai are considered in comparison with ankaramites of different geodynamic settings. The basalts of the Ust'-Sema Formation are enriched in phenocrysts of high-Mg clinopyroxene (Mg# ≤ 94) (20 to 40-50 vol.%) with a high content of Cr2O3 (up to 1.11 wt.%), enclosed in the clinopyroxene--plagioclase microlitic groundmass. In addition, there are minor phenocrysts of saussuritized plagioclase (An49-71), olivine replaced by secondary minerals, amphibole with Mg# = 55.7-68.2, and Cr-spinel with Cr# = 36.2-41.7. Inclusions of Cr-spinel in high-Mg clinopyroxene are richer in Cr (Cr# ≤ 72.8). The basalts of the Ust'-Sema Formation are chemically heterogeneous and are subdivided into two main groups: high-Ca (MgO = 7.98-14.77 wt.% and CaO/Al2O3 = 1.0-1.8) and low-Ca (MgO = = 2.84-9.89 wt.% and CaO/Al2O3 = 0.2-0.9). The obtained data on the high-Ca basalts of the Ust'-Sema Formation show that the rocks are similar to the reviewed ankaramites and thus can be assigned to this type of rocks. The low-Ca basalts of the Ust'-Sema Formation might have resulted from the fractionation of ankaramitic melt in intermediate magma chambers. The Gorny Altai ankaramites formed through the melting of the wehrlitized suprasubductional lithospheric mantle during the closure of the Paleoasian Ocean. [ABSTRACT FROM AUTHOR]

The concept of the Tommotian Regional Stage of the Siberian Platform has been closely linked to the idea of the 'Cambrian Explosion' of animals and protists when the entire Earth system shifted rapidly into Phanerozoic mode. We conducted a multidisciplinary study of an informal 'synstratotype' of the lower Tommotian boundary in the upper Mattaia Formation, Kessyusa Group in the Olenek Uplift, NE of the Siberian Platform. The Mattaia Formation characterizes an upper shoreface to inner-shelf depositional setting and provides important faunal ties and correlation with carbonate-dominated and aliminosiliciclastic open-shelf areas. A section of the upper Mattaia Formation at Boroulakh, Olenek River is suggested here as a model for the Global Boundary Stratotype Section and Point for the base of the Cambrian Stage 2. This level contains the lowermost occurrence of the cosmopolitan fossil helcionelloid mollusc Aldanella attleborensis. Section global markers near the base of the stage include a positive excursion of δ13C values reaching +5.4‰, a U–Pb zircon date of 529.7 ± 0.3 Ma, massive appearance of diverse small skeletal fossils (including Watsonella crosbyi), a sudden increase in diversity and abundance of trace fossils, as well as a conspicuous increase in depth and intensity of bioturbation. Coincidently, it is this level that has always been regarded as the lower Tommotian boundary on the Olenek Uplift. [ABSTRACT FROM AUTHOR]

The first finds of Upper Devonian radiolarians in cherty rocks of the Akbasay Formation, Zeravshan-Gissar mountainous area, are reported. Nineteen species of spherical and spiny forms were identified and assigned to 8 genera. Finds of co-occurring conodonts and radiolarians enabled the refinement of the proposed age of radiolarian associations. [ABSTRACT FROM AUTHOR]

An Erratum to this paper has been published: https://doi.org/10.1134/S1028334X23060144 [ABSTRACT FROM AUTHOR]

This paper reports the results of thermodynamic modeling of the formation of the Birkhin volcanoplutonic association by means of geochemical thermometry. The obtained liquid line of descent for the magma chamber of the Birkhin Massif indicates that the melt evolved into the field of subalkaline composition. The melts of the volcanics of the Tsagan-Zaba complex are identical to the melts in the magma chamber in both major components and REEs. It was concluded that the Birkhin and Tsagan-Zaba complexes are comagmatic. A scenario was proposed for the development of the Birkhin volcanoplutonic association involving multiple eruptions of volcanic rocks during its formation. It was shown that the intermediate rocks are not derivatives of basic magmas, but were produced by interaction of basic volcanic rocks with felsic intrusions cutting them. [ABSTRACT FROM AUTHOR]

Abstract We consider a hypothesis for the origin of PGE-bearing ultramafic rocks of the Inagli massif (Central Aldan) through fractional crystallization from ultrabasic high-potassium magma. We studied dunites and wehrlites of the Inagli massif and olivine lamproites of the Ryabinovy massif, which is also included into the Central Aldan high-potassium magmatic area. The research is focused on the chemistry of Cr-spinels and the phase composition of Cr-spinel-hosted crystallized melt inclusions and their daughter phases. Mainly two methods were used: SEM-EDS (Tescan Mira-3), to establish different phases and their relationships, and EPMA, to obtain precise chemical data on small (2-100 μm) phases. The obtained results show similarity in chromite composition and its evolutionary trends for the Inagli massif ultramafites and Ryabinovy massif lamproites. The same has been established for phlogopite and diopside from crystallized melt inclusions from the rocks of both objects. Based on the results of the study, the conclusion is drawn that the ultramafic core of the Inagli massif resulted from fractional crystallization of high-potassium melt with corresponding in composition to low-titanium lamproite. This conclusion is consistent with the previous hypotheses suggesting an ultrabasic high-potassium composition of primary melt for the Inagli ultramafites. [ABSTRACT FROM AUTHOR]

Abstract An assemblage of Cr-spinels widespread in Carnian (Upper Triassic) diamondiferous deposits in the northeastern Siberian Platform is studied. Analysis of their morphology and chemical composition has revealed two dominant varieties of Cr-spinels and has demonstrated certain regularities in their distribution in the study area. Correlations have been established between the areal distribution of the recognized types of Cr-spinels and diamond varieties typical of kimberlite sources and between the distribution of Cr-spinels and rounded diamond dodecahedrons. The phase and chemical compositions of polyphase inclusions in the Cr-spinels are studied. The spatial arrangement of inclusions along the crystal growth zones indicates their primary genesis and trapping from the melt during crystallization. Compositional features of some minerals in the inclusions—SiO 2 impurity in apatite and high CaO contents (0.2-0.8 wt.%) in olivines—point to a nonkimberlite source of these Cr-spinels. The presence of K- and Na-containing phases and calcite in the inclusions indicates saturation of the initial melt with alkalies, Ca, and CO 2. The data obtained suggest that the numerous Late Vendian diatremes in K-rich alkaline basites of the Olenek Uplift area are the source of the dominant Cr-spinel variety. [ABSTRACT FROM AUTHOR]

Obtained data shows that high-potassic dyke rocks of the Ryabinoviy massif (Central Aldan) belong to low-titanium lamproite series (Mediterranean type) and are distinct with “classic” high-titanium lamproites. Based on Al-in-olivine thermometer, temperature of olivine-chrome-spinel pair crystallization varies in range between 1100 and 1250°C. This suggests lithospheric mantle source for the parental melt and makes role of mantle plume insignificant. High-precision data on olivine composition and bulk rock traceelement composition imply mixed source for the parental melt, consisted of depleted peridotite and enriched domains, originated during ancient subduction. [ABSTRACT FROM AUTHOR]

We present new data on the U-Pb age of zircons, geochemistry of trace elements, and isotope (Nd, Sr, O) composition of rocks of the Kogtakh gabbro-monzonite complex on the eastern slope of the Kuznetsk Alatau Ridge. The established age of zircon in the rocks of the main intrusive phases (500-480 Ma) is taken as the time of formation of the Kogtakh complex in the Late Cambrian-Early Ordovician, during the accretion-collision stage of evolution of the Central Asian Orogenic Belt. The distribution and ratios of LILE and HFSE in the rocks suggest that the intrusions proceeded under interaction of the PREMA + EM/OIB mantle plume and the suprasubductional lithospheric IAB mantle. The mantle-crust interaction led to the heterogeneous isotopic composition of neodymium in the magma source (ɛ Nd ( T ) ~ 3.5-5.4). The mixing of different mantle and continental-crust materials resulted in an increase in isotope parameters: ( 87 Sr/ 86 Sr) T ~ 0.7039-0.7052, ɛ Sr ( T ) ~ 0-19, and δ 18 O ~ 6.5-8.8 ‰ (SMOW). The REE ratio in the least differentiated gabbroids indicates different depths of probable magma chambers and the formation of their primary (Tb/Yb PM > 1.8) mafic melts at different degrees of melting of the model garnet peridotite. [ABSTRACT FROM AUTHOR]

A comparative study of the chemical compositions of chromium spinel and polyphase inclusions has been carried out. Chromium spinels were separated from the concentrate of the Carnian Stage (T3) rock sample collected at the northeastern fringe of the Siberian platform. The chromium spinels show a wide variety of compositions, most of which are of the “Kurung” type, which is considered to be a deceptive indicator of a kimberlite. They contain inclusions in the size range of 10-100 μm and contain several mineral phases. The most frequent inclusions are olivine and clinopyroxene; additional phases are nepheline, K-Fsp, Ti-Mg-Ca-amphibole, Ti-biotite (phlogopite), apatite and perovskite. Ilmenite and iron sulfides are less common. The data obtained on the composition of these inclusions indicate differences in the conditions of their formation and possibly different types of parental sources. A possible type of provenance source could be potassium alkali basites. [ABSTRACT FROM AUTHOR]

The age of the Paleozoic sedimentary successions of the Yuryung-Tumus Peninsula in the Khatanga Gulf is determined as Middle Devonian, late Eifelian, and the beginning of the early Givetian on the basis of the study of brachiopods, ammonoids, nautiloids, bactritoids, gastropods, and conodonts, and in the terminology of the standard conodont succession, these deposits are not older than the late Eifelian Tortodus kockelianus Zone, but include the terminal Eifelian Polygnathus ensensis Zone and the first Givetian Polygnathus hemiansatus Zone and are no younger than the beginning of the early Givetian Polygnathus varcus Zone. The Middle Devonian sedimentary successions of the Yuryung-Tumus Peninsula show the level of the global sedimentary Kačak Event. The areas of distribution of the Devonian sedimentary deposits in the Yuryung-Tumus Peninsula in the Khatanga Gulf should be considered as one of the fragments of the regional geological structures of a remote (isolated?) region of the Taymyr Fold System rather than a component of the structures of the northern Siberian Platform. [ABSTRACT FROM AUTHOR]

We consider geochemical features of mafic magmatism manifested during the evolution of a complex nappe-folded structure in Western Sangilen, resulted from the Cambrian-Ordovician collisional tectogenesis. There are abundant ultramafic-mafic and mafic associations of different types in this region: layered low-Ti low-alkali ultramafic-mafic intrusions, high-Ti medium-alkali gabbroids, gabbro-monzodiorite intrusions, and alkali basalts. Isotope-geochronological data showed that these complexes formed over a wide time interval, from 570 to 440 Ma. At this time, the geodynamic setting in Western Sangilen changed from an island-arc one via a collision one to an intercontinental rift setting. At the early and late stages of the evolution of Western Sangilen, the geochemical features of mafites were typical of their geodynamic settings. The properties of mafites that formed synchronously with the collision are of particular interest. The studies have shown that the chemical composition of collisional mafites of Western Sangilen changed with time. They became richer in alkalies, titanium, and incompatible elements. This fact indicates a change in the type of mantle source from suprasubductional in the Cambrian to enriched deeper-level one in the Ordovician. [ABSTRACT FROM AUTHOR]

The belemnite Sr isotope characteristics obtained over an interval from the Upper Volgian Regional Substage to the lower part of the Ryazanian Regional Stage in the section on the Maurynya River (Western Siberia) fills a gap in the Sr/Sr ocean water variation curve over the Jurassic-Cretaceous boundary. The increase in the Sr/Sr values from 0.707172 to 0.707242 revealed in the section coincides with a general rise in this ratio in the Late Jurassic-Early Cretaceous ocean. [ABSTRACT FROM AUTHOR]

We conducted isotope–geochemical studies of the Upper Devonian of the Rudny Altai. Whole-rock carbon isotope analyses of the studied section represented by carbonate fore-reef facies reveal a negative excursion at the base of punctata Zone. When compared to conodont biofacies turnovers and the Upper Devonian events chart, the new data have demonstrated a synchronism between the negative excursion and the coeval decline in conodont biodiversity corresponding to the Middlesex anoxic event of the Frasnian Stage of the Upper Devonian. [ABSTRACT FROM AUTHOR]

Abstract: The first detailed isotope-geochemical study of carbonate deposits has been performed in the Lower Famennian stratotype section of the northwestern Kuznetsk Basin (Kosoy Utyos), which was localized in the middle latitudes of the Northern Hemisphere in the Late Devonian. The δ13Ccarb, δ13Corg, and δ18O variation curves were constructed for the section deposits. Geochemical and petrographic studies of carbonates allowed allocation of samples that underwent postsedimentation alteration and exclude them from further interpretation. Compared with coeval sections in the other world''s regions, the Kosoy Utyos section is characterized by higher δ13Ccarb values, up to 5.4‰, whereas the maximum value in subequatorial area sections is 4‰. The isotope shift amplitude of the studied section reaches 4.6‰, which is 1.5‰ higher than those in other regions. The δ18O values are 3‰ lower than the ones of the world''s coeval sections. The results obtained show that δ13C and δ18O variation trends differ from those of coeval subequatorial sections. The high shift amplitude and maximum δ13Ccarb values in the Kosoy Utyos section are due to the shallow-water carbonate sedimentation environments on the Siberian continental shelf and, probably, the lower temperatures of waters in the middle latitudes as compared with the subequatorial areas. [Copyright &y& Elsevier]

This study aims at summarizing available geological and geochemical data on known Proterozoic platinum-bearing ultramafic-mafic massifs in the south of Siberia. Considering new data on geochemistry and geochronology of some intrusions, it was feasible to compare ore-bearing complexes of different time spans and areas and to follow their relationships with the recognized large igneous provinces. In the south of Siberia, the platinum-bearing massifs might be united into three age groups: Late Paleoproterozoic (e.g., Chiney complex, Malozadoisky massif), Late Mesoproterozoic (e.g., Srednecheremshansky massif), and Neoproterozoic (e.g., Kingash complex, Yoko-Dovyren massif, and massifs in the center of the East Sayan Mts.). In most massifs but Chiney the initial magmas are magnesium-rich. On paleogeodynamic reconstructions, the position of the studied massifs is the evidence that three most precisely dated events in North Canada continued into southern Siberia: In the period 1880-1865 Ma, it was the Ghost-Mara River-Morel LIP; at 1270-1260 Ma, the Mackenzie LIP; and at 725-720 Ma, Franklin LIP. In Siberia, the mostly productive massifs with respect to PGE-Ni-Cu mineralization are those linked with the Franklin LIP: Verkhny Kingash, Yoko-Dovyren, and central part of the Eastern Sayan Mountains, e.g., Tartay, Zhelos, and Tokty-Oy. [ABSTRACT FROM AUTHOR]

We have revealed the spatio-temporal regularities of distribution of platinum group elements (PGE) in basaltoids related to the activity of the Siberian mantle plume. As objects of study, we chose rift and flood basalts from the Norilsk district (sampled from the SD-9 borehole), flood basalts from the central part of the Tunguska syneclise (Lower Tunguska), Kuznetsk Basin traps, and subalkalic basalt from the Semeitau volcanoplutonic structure in eastern Kazakhstan. Based on the PGE patterns of basaltoids related to the activity of the Permo-Triassic Siberian plume, we have shown that the rocks that formed in the central part of the Siberian Large Igneous Province (LIP) at the early rift stage have low contents of PGE, whereas picrites and tholeiitic flood basalts have high contents. The rift (Semeitau structure) and flood (Kuznetsk Basin traps) basalts from the peripheral regions are characterized by extremely low PGE contents. The high PGE contents in magmas of the plume head are responsible for the high productivity of ultramafic-mafic trap magmatism. The elevated K contents in magmas and the high PGE contents in the mantle plume head are probably due to the ascent of deep-seated material from the core-lower-mantle boundary, as follows from the thermochemical model of the Siberian plume. [ABSTRACT FROM AUTHOR]

The results of the first study of the PGE distribution in deformed lherzolites of the Udachnaya kimberlite pipe (Yakutia) are presented here. The complex character of evolution of the PGE composition in the Deformed lherzolites is assumed to be the result of silicate metasomatism. At the first stage, growth in the amount of clinopyroxene and garnet in the rock is accompanied by a decrease in the concentration of the compatible PGE (Os, Ir). During the final stage, the rock is enriched with incompatible PGE (Pt, Pd) and Re possible due to precipitation of submicron-sized particles of sulfides in the interstitial space of these mantle rocks. [ABSTRACT FROM AUTHOR]

The study provides new petrologic and isotope geochemical data for rocks of the 465 ± 5 Ma Bulka massif (Borodina et al., 2011). The primary amphibole from granitoid stocks cutting across the layered series of the massif yielded an Ar-Ar age of 415.9 ± 3.7 Ma. The rocks of the Bulka massif have Nd/Nd ratio of 0.513243 and εNd (Т) values of +12.00. The granitoids have Nd/Nd ratios between 0.512919 and 0.512961 and εNd (Т) values between +8.03 and +9.25. The Nd isotope composition indicates that the rocks of the Bulka massif and granitoids were derived from a depleted mantle source. Depletion of the rocks of the massif in LILE, LREE, and HFSE over LILE is inherited from the mantle source, which has geochemical signatures of N-MORB and subduction-related components. Granitoids are metaluminous I-type granites, which were probably generated either by differentiation of intermediate to mafic mantle-derived magmas or by melting of metabasites. The rocks of the granitoid stocks are characterized by enrichment in LILE and LREE and depletion in HFSE over LILE, which suggests derivation from arc-related parental magmas. [ABSTRACT FROM AUTHOR]

We report the first data on 40 Ar/ 39 Ar dating, trace-element geochemistry, and isotope (Nd, Sr, O) composition of the Belaya Gora gabbro-foidolite-foyaite intrusive massif, one of typical representatives of the alkaline province of the northeastern Kuznetsk Alatau. The established age of rock-forming amphibole, ~ 401-403 Ma, is taken as the time of the pluton formation in the EarlyDevonian.Thedistribution and ratios of LILE and HFSE in the rocks suggest that the intrusion took place in the setting of “superposition”of Devonianmantle plume on the Early Paleozoic accretion-collision complexes. Therefore, the source of magmatic products had a heterogeneous composition as a result of mixing of plume material with the substances of suprasubduction and crustal substrates. The mantle component might have been a PREMA + EM combination, which is confirmed by the parameters of the Nd isotope composition (£ N dT - 3.2-4.6; T N d(DM) - 0.8 Ga) of alkaline rocks. 878618 The effects of crustal contamination are reflected in the high ratios of strontium and oxygen isotopes ( Sr/ Sr) T - 0.7046-0.7054; 5 O - 8.5-9.2%c, SMOW). [ABSTRACT FROM AUTHOR]

We present the results of a study of the geologic structure and age sequence of formation of the Late Neoproterozoic-Early Paleozoic plagiogranitoid and gabbroid associations in the Bumbat-Hairhan intrusive area of the Lake Zone in Western Mongolia. The petrogeochemical characteristics of the plagiogranitoids provide information about the conditions of formation of their parental melts at the island-arc and accretion-collision stages of the regional evolution. They also help to establish the main magma-generating sources as well as the major mechanisms of large-scale formation of granitoid melts and their relationship with ore generation processes. According to the trace-element and REE patterns and indicative ratios of these elements, the plagiogranitoids are subdivided into high- and low-alumina ones. Among the island-arc plagiogranitoids (551–524 Ma) of the Bumbat-Hairhan area, high-alumina varieties are the most widespread. They resulted from the partial melting of metabasites in equilibrium with garnet-containing restite at > 15 kbar during their subsidence into the subduction zone. In geochemical features these plagiogranitoids are similar to high-Si adakites of different world regions. Island-arc low-alumina plagiogranitoids are scarcer. Their geochemical characteristics indicate that the parental melts were generated through the partial melting of metabasites in the lower part and/or in the basement of the island-arc system in equilibrium with amphibole-containing restite at < 8 kbar. Plagiogranitoid associations of the accretion-collision stage (511–468 Ma) are the most widespread in the Bumbat-Hairhan area. They are subdivided into high- and low-alumina ones. According to the contents of trace elements and their indicative ratios, the low-alumina plagiogranitoids resulted from the partial melting of metabasites in equilibrium with plagioclase-containing restite at < 8 kbar in the upper part of the collisional structure, and the high-alumina ones were generated through the melting of metabasites in the basement of thick crust in equilibrium with garnet-containing restite at > 15 kbar. Geochronological studies in the Bumbat-Hairhan area revealed two stages of ore-generating processes spatially and temporally related to the formation of low-alumina plagiogranitoids. The early stage (518 ± 5 Ma), development of vein Cu (Au) mineralization, coincided in time with the formation of island-arc low-alumina plagiogranitoids of the Darbi massif (~ 524 Ma). The late stage (456 ± 4 Ma), formation of porphyry Cu-Mo (Au) mineralization, was synchronous with the formation of the low-alumina plagiogranites at the accretion-collision stage (~ 468 Ma). [ABSTRACT FROM AUTHOR]

We report first results of a systematic study of carbon isotope fractionation in a carbonate fluid system under mantle PT conditions. The system models a diamond-forming alkaline carbonate fluid using pure sodium oxalate (NaCO) as the starting material, which decomposes to carbonate, CO and elementary carbon (graphite and diamond) involving a single source of carbon following the reaction 2NaCO → 2NaCO + CO + C. Near-liquidus behaviour of carbonate was observed at 1300 °C and 6.3 GPa. The experimentally determined isotope fractionation between the components of the system in the temperature range from 1300 to 1700 °C at 6.3 and 7.5 GPa fit the theoretical expectations well. Carbon isotope fractionation associated with diamond crystallisation from the carbonate fluid at 7.5 GPa decreases with an increase in temperature from 2.7 to 1.6 ‰. This trend corresponds to the function Δ = 7.38 × 10 T. [ABSTRACT FROM AUTHOR]

The Ta Nang gold deposit is localized in Middle Jurassic black shales. The ore zone is a series of layer-by-layer crush zones and zones of hydrothermal rock alteration, < 10 m in thickness and > 2 km in length. It consists of quartz-sulfide veins, sulfidized black shales, and their hydrothermally altered varieties. Sulfide mineralization occurs as two assemblages: early pyrite-arsenopyrite and late chalcopyrite-sphalerite- galena. The pyrite-arsenopyrite assemblage is composed of different morphogenetic varieties. Coarse-crystalline arsenopyrite and pyrite aggregates and metacrystals of different orientations, 0.1 to 10 mm in size, are the most widespread. The chalcopyrite-sphalerite-galena assemblage is scarce. Along with the main ore minerals, it includes more rare minerals: pyrrhotite, lead sulfosalts (tsugaruite), and gold, which form a spatial assemblage with the main minerals or small inclusions in them. Gold occurs mainly as fine dissemination in cracks in pyrite, arsenopyrite, chalcopyrite, and quartz. Gold content in sulfidized carbonaceous shales is no more than tenths of ppm, averaging 0.38 ppm. This content in the quartz veins is considerably higher, averaging 3.92 ppm. Silver contents in the shales and quartz veins are similar and equal to 2.68 and 5.30 ppm, respectively. Also, the sulfidized rocks and veins have elevated contents of Fe, As, Pb, Zn, Cu, Cd, Ni, and Co; most of these elements (Fe, As, Pb, Zn, and Cu) make up their own sulfide minerals, and the others are trace elements. According to 39 Ar/ 40 Ar dating of sericite from the quartz-sulfide veins, their age is 129.3 ± 5.6 Ma, which is close to the age of the Cretaceous granite intrusions of the Deo Ca complex. These veins formed from moderately strong solutions (11.7-6.4 wt.% NaCl equiv) with the CH 4 + N 2 + CO 2 gas phase at 340–130 °C. Judging from the S isotope composition (5 34 S = 1.6-4.3%c), predominantly deep-seated endogenic sulfur participated in the formation of ore sulfide associations. Analysis of the distribution of gold shows that it was deposited together with sulfide minerals (galena, sphalerite, and chalcopyrite) at a later stage. [ABSTRACT FROM AUTHOR]