Magnetotelluric studies of the East-European Craton and adjacent regions

Magnetotelluric method is widely applied to study the Russian part of the East-European Craton, as well as the Caucasus and the Urals: several thousand soundings were performed during the last few years. Their periods range is approximately from 0.003 to 3000 seconds, which allows to study the sedimentary cover and the consolidated crust. Resistivity cross-sections along several regional profiles which run across the tectonic structures of the East-European Craton and the adjacent folded systems were obtained, mainly using 1D and 2D interpretational tools. MT investigations provided important information about the structure and reservoir properties of sedimentary complexes, the state of active geodynamic regions, the graphitization and fluid regime of the consolidated crust, and the permeable and fluid-saturated crustal zones.     

No-z Approximation and rz-Model for Studying Magnetic Fields in Astrophysical Objects

Astronomy Reports - Different astrophysical objects, such as the Sun, another stars, galaxies and accretion discs have regular magnetic field structures. Their generation is usually connected with...     

Deep Electrical Conductivity in the Vicinity of the Orsha Depression: 2D REBOCC Inversion of Synthetic and Observed Magnetotelluric Data

Izvestiya, Physics of the Solid Earth - Abstract—The geoelectric structure of the junction region between three largest segments of the East European Craton (EEC)–Volga–Uralia,...     

Global VLBI polarisation observations of BL Lac objects

In May 1995, we obtained 5-GHz VLBI polarisation observations of 20 sources in the complete sample of BL Lac objects defined by H. Kühr and G. Schmidt. Ten antennas participated in the global VLBI observations. Total intensity and linear polarisation images of five sources have been made and analysed thus far. The images for 0003–066, 1538+149, and 2254+074 are presented, together with an analysis of the evolution of their polarisation structure and estimates of apparent velocities for components in their VLBI jets.     

Laser-like wave amplification in straits

Ocean Dynamics - We present research on the excitation of ocean surface wind waves in non-homogeneous situations, for the case of a deep water strait in the presence of a constant wind, blowing...     

The age of late orogenic granitoids of the urals based on U-Pb isotope dating of zircons (Exemplified by the Shartash and Shabry massifs)

U-Pb dating of zircons (SHRIMP-II) has been performed for the first time for granites, granodiorites, and synplutonic granodiorite and melanodiorite bodies of the Shartash and Shabry massifs in the Middle Urals. The time of the formation of the massifs is 300–306 Ma, which is 25 Ma younger than the previous estimates. The age data obtained are in line with the time of the formation of the adamellite-granite series of the Verkhisetsk Batholite (the master sample of tonalite-granodiorite-granite magmatism in the Middle Urals), the series of which is petrochemically close to the rocks of the massifs.     

Nature of the chemical heterogeneity of the continental lithospheric mantle

The paper reports data on the chemical composition of mantle peridotite xenoliths from kimberlites and alkaline basalts that represent the continental lithospheric mantle (CLM) beneath Early Precambrian and Late Proterozoic-Cenozoic structures, respectively. In order to identify compositional trends during the melting of primitive material and propose the most reliable criteria for constraining the conditions of this process and its degree, we analyzed literature data on the melting of spinel and garnet peridotites within broad temperature and pressure ranges. It was determined that the degree of melting (F%) of pristine peridotite of composition close to that of the primitive mantle (PM) can be deduced from the Mg/Si and Al/Si ratios in the residue; an equation was proposed for evaluating F from the Mg/Si ratio. The Ca/Al ratio of residues at low (1–1.5 GPa) pressures and degrees of melting from 2–3 to 20–25% increases several times but decreases with increasing F at pressures higher than 3 GPa. The Na partition coefficient between melt and residue decreases at increasing pressure and approaches one at a pressure close to 20 GPa. Residues after low-degree melting are strongly depleted in Ti, Zr, Y, and Nb but are enriched in Cr. The application of these criteria to the composition of xenoliths brought to the surface from the mantle occurring beneath tectonic structures of various age led us to conclude that compositional heterogeneities of CLM (particularly the variations in the concentrations of major and certain siderophile elements) are controlled, first of all, by the melting of the mantle source material. These processes occurred under various thermodynamic conditions (T, P, and $ f_{O_2 } $ f_{O_2 } ) and differed in their intensity, and this predetermined the compositional diversity of the residual mantle material (its concentrations of Mg, Al, Si, Ca, Na, K, Ni, Co, V, and Cr). Our results are principally consistent with the hypothesis of the global magmatic ocean. It is thought that the early phases of its consolidation were variably controlled by the fractionation of minerals, for example, majorite. Moreover, heterogeneities in the distribution of siderophile elements could be partly predetermined by changes in the properties of these elements at ultrahigh temperatures and pressures. The processes of partial melting were the most intense during the early evolution of the mantle (perhaps, in the Early Precambrian), and hence, the mantle has different chemical composition beneath Archean cratons and Phanerozoic foldbelts.