Evolution of the Barents Sea basin and oil and gas potential of coastal zones in the Kola region

The perspectives of development of the Varanger–Timan petroleum basin are considered. The Varanger–Timan oil-and-gas basin was formed in the Riphean and Vendian on the passive continental margin of the East European Plate. Evolution of the Barents–Kara region in the Mesoproterozoic and Neoproterozoic led to a mosaic junction of the lithospheric plates having different ages and having undergone significant alterations during the Caledonian and Variscan orogenies. The spatiotemporal regularities of the interaction between geodynamic processes and conditions providing for the formation of conventional and unconventional hydrocarbon fields are described.     

Large-volume platinum ore deposits in zonal mafic-ultramafic complexes of the Ural-Alaskan type and the outlook for their development

The results of mineralogical-technological studies of PGM mineralization in zonal mafic-ultramafic complexes of the Ural-Alaskan type are given. All studied massifs in the Urals and Kamchatka are characterized by similar evolution of mineral assemblages. The chromite (platinum-chromitite-dunite) and dunite (platinum-pegmatoid dunite) geological-economic types of small platinum deposits and occurrences are separate enriched sites (ore shoots) of large-volume platinum ore deposits. These are rather thick and extended zones of recrystallized dunites with attributes of high-temperature structural deformations and intense fluid reworking. Low Pt grade in ore (<0.5 gpt) is determined by fine and very fine (grain size class — 80 μm) euhedral PGM crystals distributed rather uniformly in ore mass. The high and occasionally anomalous Pt contents (up to 1 kgpt and higher) are related to large xenomorphic segregations of PGM, which concentrate largely in the marginal parts of separate chromite segregations. The significant part of productive Pt-bearing mineralization is hosted in olivine matrix of igneous rocks, so that recovery of platinum cannot be associated only with separation of chromite ore. The direct gravity concentration of platinum ore without preliminary separation of chromite concentrate is recommended as the main technique of platinum recovery. The technological scheme provides for two-stage comminution of ore with between-cycle separation of coarse the PGM fraction into the concentrate as a commodity product. The results obtained allow us to regard the aforementioned mineralization as a new geological and economic type of lode platinum deposits, whose potential is comparable with active platinum reserves in the complex Cu-Ni ores of the Noril’sk district.     

Coupled guided modes in the magnetotails: spatial structure and ballooning instability

The problem of the spatial structure of coupled azimuthally small-scale Alfvén and slow magnetosonic (SMS) waves is solved in an axisymmetric magnetotail model with a current sheet. It is shown that the linear transformation of these waves occurs in the current sheet on magnetic field lines stretched into the magnetotail. From the ionosphere to the current sheet these modes are linearly independent. Due to the high ionospheric conductivity the structure of coupled modes along magnetic field lines represents standing waves with very different typical scales in different parts of the field line. In most of the field line their structure is determined by the large-scale Alfvén wave structure. Near the ionosphere and in the current sheet, small-scale SMS wave field starts to dominate. In these regions coupled modes becomes small-scale. Such modes are neutrally stable on the field lines that do not cross the current sheet, but switch to the ballooning instability regime on field lines crossing the current sheet. An external source is required to generate these modes and this paper considers external currents in the ionosphere as a possible driver. In the direction across magnetic shells the coupled modes are waves running away from the magnetic shell on which they were generated.     

First Finds of Native Iridium in Chromite–Platinum Ledge Ore and Placers of Zonal Clinopyroxenite–Dunite Massifs of the Urals

Doklady Earth Sciences - The results of studying the aggregates of native iridium from chromitites of the Svetloborskii and Sosnovskii clinopyroxenite–dunite massifs of the platinum-bearing...     

Nature and Age of Detrital Zircons from Rocks of the Shear Zone: The Problem of Occurrence of the Archean Basement in the Transangarian Yenisei Ridge

Petrogeochemical and geochronological study of boudined quartzite sandstones and tonalites, as well as host amphibolites, in the shear zone showed that potential sources of detrital zircons were Neoarchean–Paleoproterozoic rocks of the Angara–Kan block and products of their metamorphism. Interpretation of the available data does not confirm the inferred presence of the Early Precambrian basement of the Siberian Craton in the Transangara region.     

Infrared Spectroscopy and Internal Structure of Diamonds from the Ichetyu Placer,Central Timan,Russia

Geology of Ore Deposits - A wide range of model temperature, which is typical for dodecahedroids from placer deposits in the Urals, Brazil, and the northern Yakutia diamond province has been...     

Grenville tectonic events and evolution of the Yenisei Ridge at the western margin of the Siberian Craton

Geological, petrologic, geochemical, and isotopic geochronological evidence for Grenville events at the western margin of the Siberian Craton are considered. These events were related to assembly of the Rodinia supercontinent. Multiple manifestations of riftogenic and within-plate magmatism at the final stage of orogenic evolution gave rise to breakdown of Rodinia and the formation of the Paleoasian ocean. The results allowed us to develop a new concept on the Precambrian geological evolution of the Yenisei Ridge and the processes that created its tectonic structure. The chronological sequence of events in the history of the Transangarian Yenisei Ridge is based on geological evidence and isotopic dating of Precambrian complexes variable in geodynamic nature. Four tectonic stages dated at 1.4?1.1, 1.1?0.9, 0.90?0.85, and 0.8?0.6 Ga were controlled by collision and extension recognized from large regional linear crustal structural elements. The evolution of the Transangarian Yenisei Ridge, which lasted for ～650 Ma, corresponds in duration to supercontinental cycles that begin from rifting and breakdown of the predated supercontinent and was completed by orogeny and the formation of a new supercontinent. The regional geodynamic history correlates with the synchronous sequence and similar style of tectonothermal events at the periphery of the large Precambrian Laurentia and Baltica cratons. This is evidenced by paleocontinental reconstructions, which confirm close spatiotemporal links of Siberia with cratons in the northern Atlantic 1400?600 Ma ago and indicate incorporation of the Siberian Craton into the ancient Nuna and Rodinia supercontinents.     

Effects of shock-wave loading in oxides

This paper reports results of experimental study of the influence of shock waves on the structure, ion valence, and phase composition of oxides, including the minerals tenorite (CuO) and hausmannite (Mn₃O₄) and perovskite-structured manganite LaMnO₃. Shock-wave loading (SWL) was modeled by explosion experiments in spherical and cylindrical (in the case of tenorite) configurations. The results of strong quasi-static shear deformations of oxides under pressure are also given for comparison. The main focus was the investigation of shock wave-induced changes in oxides at the level of chemical bonds, disturbances of ionic composition and stoichiometry, relation of these processes to the formation of micro(nano)structures in the minerals, and stages and microscopic mechanisms of the development of new dense phases. It was shown that SWL-affected oxides can be successfully investigated by various methods of X-ray spectroscopy (photoelectron, absorption, and emission) and nuclear techniques (Rutherford back scattering, nuclear reaction analysis, and positron annihilation spectroscopy). Crystal structure and phase composition were explored by X-ray and neutron diffraction methods. Microscopic structures were investigated by optical, scanning electron, and scanning tunneling microscopy. It was shown that the effects of SWL are initially manifested in oxides as a stoichiometry violation, an increase in the number of low-valence cations, and formation of a micro(nano)structure. Plastic deformations developed during SWL are especially important for these processes. The decomposition of oxides during the solid-phase stage of shock metamorphism under the influence of high pressures, temperatures, and severe plastic deformations produces oxides with a low degree of oxidation and free oxygen, which can migrate over considerable distances to form new compounds. The ultradeep penetration of particles of the surrounding matrix into the target mineral during SWL can also serve as a mechanism of shock metamorphism at the solid-phase stage of transformation.     

On the Role of the Explosive Interaction of Three Surface Waves at the Initial Stage of Spray Generation in Strong Winds

Izvestiya, Atmospheric and Oceanic Physics - This work is devoted to a theoretical study of the hydrodynamic instability of the water–air interface. The development of this instability may...