Arsenocolusite in Pyrite Ores of the Saum Copper–Zinc Massive Sulfide Deposit,North Urals

Geology of Ore Deposits - Pyrite ores on the flanks of the Saum copper–zinc massive sulfide deposit are clastic sediments intensely transformed under conditions of acid diagenesis. Colusite...     

Stability of Current Sheets in the Solar Corona

This work aims at investigating unstable modes of oscillation of quasi-vertical two-dimensional current sheets with sheared magnetic fields under physical conditions typical for the solar corona. We use linear magnetohydrodynamic equations to obtain sets of unstable modes related to the longitudinal inhomogeneity of the current sheet. It is shown that these modes of current sheet oscillations can modulate the current sheet thickness along the polarity inversion line. Based on the obtained results, we propose a scenario which can naturally explain both the quasi-periodic pulsations of hard X-ray emission and the parallel movement of their double footpoint-like sources along the polarity inversion line observed in some eruptive two-ribbon solar flares.     

The three-dimensional shear velocity structure of lithosphere in the southern Baikal rift system and its surroundings

The three-dimensional shear velocity lithospheric structure at depths from 0 to 70 km beneath the southern Baikal rift system and its surroundings has been imaged by inversion of P-to-SV receiver functions from 46 digital stations operated in two teleseismic international projects in southern Siberia and Mongolia. The receiver functions were determined from teleseismic P waveforms and inverted to obtain depth dependences of S velocities at each station which were related to tectonic structures. The computed vertical and horizontal sections of the 3D shear velocity model imaged a transition from relatively thin crust of the southern Siberian craton to thicker crust in the folded area south and southeast of Lake Baikal, with a local zone of thin crust right underneath the South Baikal basin. The velocity structure beneath the Baikal rift, the mountains of Transbaikalia, Mongolia, and the southern craton margin includes several low-velocity zones at different depths in the crust. Some of these zones may record seismic anisotropy associated with mylonite alignment along large thrusts.     

Sulfide Mineralization Hosted by Spurrite-Mervinite Marbles (Kochumdek River,East Siberia)

Doklady Earth Sciences - Marbles of the Kochumdek complex contain pyrrhotite, rasvumite, alabandine, würtzite, galena, and acanthite. The diversity of sulfides is caused by efficient crystal...     

Depth-integrated and depth-resolved models of Kara Sea primary production

Primary production (PP) models of the Kara Sea are developed based on data collected on fall expeditions (September–October 1993, 2007, and 2011) and their precision assessment utilizes the dataset collected in September 2013. The algorithms for different model types (depth-integrated and depth-resolved) are compared. The depth-resolved model performs slightly better than the depth-integrated one (the rootmean- square-difference (RMSD) are 0.29 and 0.31, respectively). These algorithms utilize the daily assimilation number (DAN) and photosynthetic efficiency (ψ) as the model coefficients, and surface chlorophyll a (chl a) and photosynthetically active radiation (PAR) as input variables. These algorithms perform better than the models that use chl a alone. Our results suggest that an increase in the performance of the Kara Sea PP models depends on the input of the photophysiological characteristics of phytoplankton (DAN and ψ) and PAR. To a lesser extent, this concerns the advantages of the depth-resolved model over the depth-integrated one. The constructed region-specific Kara Sea PP models combined with satellite-derived chl a and PAR can be used to estimate annual values and long-term variation of PP in hydrologically and hydrochemically similar waters of the Arctic Ocean.     

Phytoplankton of the Khatanga Bay,Shelf and Continental Slope of the Western Laptev Sea

Oceanology - The studies were conducted along the transect (11 stations) from the inner part of Khatanga Bay in the south to the Laptev Sea continental slope in the north in September 17—20,...     

Asymmetry effect on the development of instabilities in current sheets

The possibility of the development of tearing and kink instabilities (with symmetric and asymmetric modes) in anisotropic thin current sheets (CSs) is investigated. The profiles of perturbed vector potentials and the instability growth rates have been found for the Vlasov equations in the approximation of a linear perturbation theory. The effect of plasma anisotropy and CS asymmetry on the development of these instabilities in the sheet is investigated.     

Quasi-satellite orbits in the general context of dynamics in the 1:1 mean motion resonance: perturbative treatment

Our investigation is motivated by the recent discovery of asteroids orbiting the Sun and simultaneously staying near one of the Solar System planets for a long time. This regime of motion is usually called the quasi-satellite regime, since even at the times of the closest approaches the distance between the asteroid and the planet is significantly larger than the region of space (the Hill’s sphere) in which the planet can hold its satellites. We explore the properties of the quasi-satellite regimes in the context of the spatial restricted circular three-body problem “Sun–planet–asteroid”. Via double numerical averaging, we construct evolutionary equations which describe the long-term behaviour of the orbital elements of an asteroid. Special attention is paid to possible transitions between the motion in a quasi-satellite orbit and the one in another type of orbits available in the 1:1 resonance. A rough classification of the corresponding evolutionary paths is given for an asteroid’s motion with a sufficiently small eccentricity and inclination.     

The types and genesis of ophicalcites in Lower Devonian olistostromes at cobalt-bearing massive sulfide deposits in the West Magnitogorsk paleoisland arc (South Urals)

Ophicalcites were earlier found in the Lower Devonian olistostromes overlapping cobalt-bearing massive sulfide deposits in the ultramafic rocks of the West Magnitogorsk paleoisland arc. They are composed of angular clastics of serpentinites and carbonates few millimeters to several centimeters in size, which are cemented with hematite-calcite and quartz-hematite-calcite matrix with aragonite, magnesite, and siderite admixtures. In chemical composition Cr-spinels from serpentinites of the ophicalcites are similar to those from the underlying serpentinites and are suprasubduction products of active continental margins. The ¹³C/¹²C and 18O/16O ratios of calcite from the breccia matrix are typical of hydrothermal deposits and are close to those of carbonate in sulfide ores and talc-carbonate metasomatites. Study of fluid inclusions from the calcite cement has shown that the ophicalcites formed from low- to moderate-temperature (100–280 °C) hydrothermal fluids as a result of postore hydrothermal emanations on ultramafic seafloor rocks similar to modern hydrothermal fields in MORs and island arcs. Hydrothermal and tectonosedimentation processes in the roof of ultramafic massifs at the vents of hydrothermal fluids led to erosion, redeposition, and cementation of ophicalcites of four types. The subsequent tectonic and gravitational processes resulted in their denudation and accumulation in olistostromes.