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Three levels of the periodicity of volcanic eruptions with different causes and effects are recognized. The first, small-scale, level lasts tens to thousands of years and is due to the periodic accumulation of melt in the intermediate chambers and its periodical effusion both for internal reasons and under the trigger effect of external factors (solar activity, tidal changes in the Earth’s rotation rate). The second, medium-scale, level lasts hundreds of thousands to millions of years and is due to the periodicity of restructuring of spreading and subduction zones. The third, largest-scale and most prolonged, level of periodicity (30-120 Ma) is related to periodic accumulations of melt at the core-mantle boundary, ascent of mantle plumes, and subsequent acceleration of convection. These reasons are probably the major regulator of the average periodicity. Acceleration of convection in the asthenosphere, caused by periodic pulses of mantle jets, determines the changes in the group of moving plates through the changes of spreading zones. The intermediate periodicity level (hundreds of thousands of years to the first millions of years) is demonstrated by the example of Kamchatka and Japan, where the periodic changes in the intensity of subduction magmatism are due to the restructuring of back-arc basins (Shikoku, Sea of Japan, and South Kuril basin).

We present a comprehensive description of the blastomylonites of the Ikat thrust localized within the Ikat terrane in the East Transbaikalian branch of the Central Asian Fold Belt. The metamorphic rocks of the Garga block are thrust over the almost unmetamorphosed Cambrian deposits of the Ikat Formation. The geologic position of the thrust and the structure and mineral and petrochemical compositions of the blastomylonites in the suture zone are considered, and U-Pb dating of detrital zircon is carried out. The blastomylonites develop after the gneisses of the Garga block; the block protolith, admixed with felsic volcanic material, was no older than the Neoproterozoic (750-800 Ma). The ³⁹Ar/ ⁴⁰Ar age of the thrust is estimated at 282 ± 0.4 Ma based on metamorphic biotite from the blastomylonites. The thrust marks the transpression period during the Late Paleozoic processes of tectonometamorphic activity related to the subsidence of the Mongol-Okhotsk oceanic crust beneath the Siberian continent.

We studied the geologic position, mineralogy, petrography, chemical composition, and age of granitoids of the Gamov batholith located in the Laoelin-Grodekovo terrane, southern Primorye (Russia). The studies have revealed four intrusive rock phases, from gabbro to leucogranites, in the massif. U-Pb zircon dating of tonalites of phase II and leucogranites of phase IV (254 ± 4 and 259 ± 2 Ma, respectively) shows that the intrusion of granitoids took place in the Late Permian without a significant gap in time. Structural investigations gave evidence for the intrusion in the sublatitudinal-compression setting. Geochemical studies have revealed granitoids of strongly different compositional types in the intrusive massif: gabbroids, quartz diorites and tonalites with characteristics of low-alumina TTG, calc-alkalic granodiorites and I-type granites, and medium-alkali leucogranites. The obtained data, together with the results of previous research into the Permo-Triassic granitoids of southern Primorye, reject the relationship of their formation with the evolution of the Solonker oceanic structures and suggest a more intricate tectonic scenario, which calls for additional study.

New data on metasomatic processes in the lithospheric mantle in the central part of the Arkhangelsk diamondiferous province (ADP) are presented. We studied the major and trace-element compositions of minerals of 26 garnet peridotite xenoliths from the V. Grib kimberlite pipe; 17 xenoliths contained phlogopite. Detailed mineralogical, petrographic, and geochemical studies of peridotite minerals (garnet, clinopyroxene, and phlogopite) have revealed two types of modal metasomatic enrichment of the lithospheric mantle rocks: high temperature (melt) and low-temperature (phlogopite). Both types of modal metasomatism significantly changed the chemical composition of the peridotites. Low-temperature modal metasomatism manifests itself as coarse tabular and shapeless phlogopite grains. Two textural varieties of phlogopite show significant differences in chemical composition, primarily in the contents of TiO₂, Cr₂O₃, FeO, Ba, Rb, and Cs. The rock-forming minerals of phlogopite-bearing peridotites differ in chemical composition from phlogopite-free peridotites, mainly in higher FeO content. Most garnets and clinopyroxenes in peridotites are the products of high-temperature mantle metasomatism, as indicated by the high concentrations of REE and their pattern in these minerals. Fractional-crystallization modeling gives an insight into the nature of melts (metasomatic agents). They are close in composition to picrites of the Izhmozero field, basalts of the Tur’ino field, and carbonatites of the Mela field of the ADP. The REE patterns in the peridotite minerals make it possible to determine the sequence of metasomatic enrichment of the lithospheric mantle beneath the V. Grib kimberlite pipe.

The paper is concerned with study of melt inclusions in minerals of ijolite xenoliths at Oldoinyo Lengai Volcano. Melt inclusions with different phase compositions occur in forsterite macrocrysts and in diopside, nepheline, fluorapatite, Ti-andradite, and Ti-magnetite crystals. Nepheline contains primary melt inclusions (silicate glass + gas-carbonate globule ± submicron globules ± sulfide globule ± daughter/trapped phases, represented by diopside, fluorapatite, Ti-andradite, and alumoakermanite). The gas-carbonate globule consists of a gas bubble surrounded by a fine-grained aggregate of Na-Ca-carbonates (nyerereite and gregoryite). Fluorapatite contains primary carbonate-rich melt inclusions in the core, which consist of nyerereite, gregoryite, thenardite, witherite, fluorite, villiaumite, and other phases. In mineral composition they are similar to natrocarbonatite. Primary melt inclusions (glass + gas bubble ± daughter phases) are rare in diopside and Ti-andradite. Diopside and forsterite have trails of secondary carbonate-rich inclusions. Besides the above minerals, these inclusions contain halite, sylvite, neighborite, Na-Ca-phosphate, alkali sulfates, and other rare phases. In addition, diopside contains sulfide inclusions (pyrrhotite ± chalcopyrite ± djerfisherite ± galena ± pentlandite). The chemical compositions of silicate glasses in the melt inclusions vary widely. The glasses are characterized by high Na, K, and Fe contents and low Al contents. They have high total alkali contents (16-23 wt.% Na ₂O + K ₂O) and peralkalinity index [molar (Na + K)/Al] ranging from 1.1 to 7.6. The carbonate-rich inclusions in the ijolite minerals are enriched in Na, P, S, and Cl. The data obtained evidence that the parental melt in the intermediate chamber was heterogeneous and contained silicate, natrocarbonate, and sulfide during the ijolite crystallization. According to heating experiments with melt inclusions, silicate-carbonate liquid immiscibility occurred at >580 °C.

The relationships and chemical compositions of silver sulfoselenides in the ores of the Rogovik gold-silver deposit (northeastern Russia) were studied to refine the low-temperature field of the Ag ₂S-Ag ₂Se phase diagram and identify contradictions between natural and experimental data. Two types of relationships between the phases of the system Ag ₂S-Ag ₂Se have been recognized using optical and scanning electron microscopy: (1) Se-acanthite and S-naumannite occur as monomineral microinclusions or fill cracks in the grains or the interstices of other minerals, and acanthite (free of impurities) forms rims on Fe-sphalerite; (2) Se-acanthite forms rims on S-naumannite. Electron probe microanalysis of silver sulfoselenides from the Rogovik ores revealed 0-7.9 wt.% Se in acanthite and 0-3.2 wt.% S in naumannite, which corresponds to the acanthite series Ag ₂S-Ag ₂S _0.76Se _0.24 and naumannite series Ag ₂S _0.28Se _0.72-Ag ₂Se. The composition ranges of the studied acanthite and naumannite series are wider than those of natural silver sulfoselenides from the Guanajuato (Mexico), Silver City (USA), Salida (Indonesia), and other deposits (Ag ₂S- Ag ₂S _0.85Se _0.15 and Ag ₂S _0.12Se _0.88-Ag ₂Se, respectively) but are significantly narrower than the composition ranges of the synthetic samples: Ag ₂S-Ag ₂S _0.4Se _0.6 and Ag ₂S _0.3Se _0.7-Ag ₂Se. The presence of intergrowths of two phases of the Ag ₂S-Ag ₂Se series in the form of Se-acanthite rims on S-naumannite in the Rogovik ores and the absence of three-phase intergrowths of silver sulfoselenides Ag ₂S _1-x Se _x from this and other deposits do not confirm the assumption on the existence of the third solid solution. The results of earlier studies of natural solid solutions Ag ₂(S,Se) show the existence of two solid solutions (of the acanthite and naumannite series) in the system Ag ₂S-Ag ₂Se and confirm the experimental data. It is necessary to carry out a detailed examination of natural silver sulfoselenides falling in the interval from Ag ₂S _0.4Se _0.6 to Ag ₂S _0.3Se _0.7 in order to identify the limits of two-phase immiscibility.

The paper is concerned with geologic processes in river valleys, such as the movement of alluvial placers and mudflows, regarded as viscous fluids. The dynamics of distribution of the placer mineral and mud-and-gravel material in a river valley was studied by modeling. Moving material was examined as an independent flow of solid particles (solid flow), free of the enclosing rocks. The flow-environment interaction was specified by mass forces, friction forces, and substance sources (drains). For the mathematical description of a solid flow, a set of viscous-liquid equations was used. The placer and mudflow parameters obtained during the numerical experiments agree satisfactorily with the full-scale data for real objects.

An effect of different mechanical activation conditions (different activator types) on the phase composition, texture characteristics of catalysts based on manganese-substituted cordierite ceramics, as well as the activity thereof in the reaction of ammonia oxidation was studied. It is demonstrated that it is preferable to use an energy-intensive planetary ball mill with a high power density, since it provides the preparation of smaller particles. The finely crystallized manganese cordierite with a minor impurities content, low specific surface, low pore volume and a high activity in the reaction of ammonia oxidation is obtained at their subsequent sintering.

A method is presented for producing nanosized oxide ferromagnetics from salt systems with the use of the mechanochemical activation and their fundamental properties are investigated. Results concerning the use of the oxide ferrimagnetics synthesized for the magnetofection of DNA, DNA/RNA sorption, microbial cells, proteins, and contrast agents for MRT diagnostics are reported. It has been found that nanoparticles are non-toxic; their distribution in internal organs and the decrease dynamics, the possibility of using them for medication transport have been demonstrated.

For the first time, an approach to a single-stage manufacture of bulky sulphide catalysts using a solid-phase method performed by means of the mechanical activation of a mixture consisting of coarse molybdenum disulphide and cobalt powders, in the presence of detonation nanodiamonds is described. An effect exerted by the mechanical treatment duration, ratio between the initial components and nanodiamonds on the process of nanofragmentation of molybdenum disulphide and activity of catalytic systems obtained in the model reaction of DBT hydrodesulphurisation has been studied.