Metamorphic evolution of ultrahigh-temperature Fe- and Al-rich granulites in the south Yenisei Ridge and tectonic implications

This study provides the first evidence for the occurrence of ultrahigh-temperature (UHT) granulite-facies metamorphism in the Yenisei Ridge (Angara–Kan block). UHT metamorphism is documented in Fe-Al-rich metapelites on the basis of the garnet–hypersthene–sillimanite–cordierite–plagioclase–biotite–spinel–quartz–K-feldspar assemblage. Microtextural relationships and compositional data for paragneisses of the Kan complex attest to three distinct metamorphic episodes: (M1) pre-peak prograde (820?900°C/5.5–7 kbar), (M2) peak UHT (920–1000°C/7–9 kbar), and (M3) post-peak retrograde (770?900°C/5.5–7.5 kbar). The observed counterclockwise P–T evolution at a high geothermal gradient (dT/dP = 100–200°C/kbar) suggests that UHT metamorphic assemblages were formed in an overall extensional tectonic setting accompanied by underplating of mantle-derived mafic magmas, which may be sourced from ~1750 Ma giant radiating dike swarms linked to the Vilyuy mantle plume as part of the Trans-Siberian LIP. The broad synchroneity of UHT metamorphism (1744 ± 26 Ma; monazite–zircon isochron age) and rift-related endogenic activity in the region can provide an additional line of evidence for the two-stage evolution of granulite-facies metamorphism in the Angara–Kan block. The Aldan–Stanovoy, Anabar, and Baikal basement inliers of high-grade metamorphic rocks within the Siberian craton record two Paleoproterozoic peaks (1.9 and 1.75 Ga) of granulite-facies metamorphism. The synchronous sequence of tectonothermal events at the periphery of the large Precambrian Laurentian, Baltica, and Siberian cratons provide convincing evidence for their spatial proximity over a wide time interval, which is consistent with the most recent paleomagnetic reconstructions of the Proterozoic supercontinent Nuna.     

Monitoring short-period internal waves in the White Sea

Widespread short-period internal wave (SPIW) activity in the White Sea has been revealed for the first time based on long-term (2009–2013) monitoring performed using satellite and in situ observations, and the statistical characteristics of these waves have been obtained. Two main regions where short-period waves constantly exist have been identified: the shelf area near the frontal zone at the boundary between the Basin and the Gorlo Strait and the shallow shelf area where the depths are about 30–50 m near Solovetskie Islands. Intense internal waves (IIWs), which are substantially nonlinear and are related to specific phases of a barotropic tide, are regularly observed near frontal zones. The wave height can reach half the sea depth and the wave periods vary from 7 to 18 min.     

The jet (pulse) model of mushroom-like flow formation

A barotropic model on the -plane is used to consider the problem of mushroom-like flow formation. The method of contour dynamics is applied to investigate the evolution of a bounded jet flow whose linear axi is identified with a rigid wall. The quasi-stationary form of the flow's head part and the velocity of its propagation have been found. The stability of the stationary solution has been studied.Translated by V. Puchkin.     

Kepler's problem in constant curvature spaces

In this article the generalization of the motion of a particle in a central field to the case of a constant curvature space is investigated. We found out that orbits on a constant curvature surface are closed in two cases: when the potential satisfies Iaplace-Beltrami equation and can be regarded as an analogue of the potential of the gravitational interaction, and in the case when the potential is the generalization of the potential of an elastic spring. Also the full integrability of the generalized two-centre problem on a constant curvature surface is discovered and it is shown that integrability remains even if elastic forces are added.     

Polynomial approximations of Berkhoff's model for waves in a basin of variable depth

On the basis of the polynomial approximation of the dispersion relation for gravity waves, a generalized version of Berkhoff's model for a non-stationary case has been obtained. The standard problem of the transition of a wave from deep water into shallow water in a basin with a slowly varying topography is applied to study analytically Berkhoff's model polynomial approximations. It has been demonstrated that all qualitative characteristics of wave transformation can be described in the framework of this model.Translated by V. Puchkin.     

Regularities of ore formation in mid-ocean ridges

The regularities of the concentration of ore matter in the mid-ocean ridges are considered, and the mechanisms of hydrothermal and cumulative treatment of the crust by ore elements are substantiated.     

Blastomylonite Complexes of the Western Yenisei Ridge (Eastern Siberia,Russia): Geological Position,Metamorphic Evolution and Geodynamic Models

Geotectonics - Metapelites and metabasites within the Yenisei regional shear zone of the Yenisei Ridge underwent strong deformations with substrate recrystallization and blastomylonite formation...     

Structural framework of the Bashkirian anticlinorium, SW Urals

The Bashkirian anticlinorium of the southwestern Urals shows a much more complex structural architecture and tectonic evolution than previously known. Pre-Uralian Proterozoic extensional and compressional structures controlled significantly the Uralian tectonic convergence. A long-lasting Proterozoic rift process created extensional basement structures and a Riphean basin topography which influenced the formation of the western fold-and-thrust-belt with inversion structures during the Uralian deformation. A complete orogenic cycle during Cadomian times, including terrane accretion at the eastern margin of the East European platform, resulted in a high-level Cadomian basement complex, which controlled the onset of Uralian deformation, and resulted in intense imbrication and tectonic stacking in the subjacent footwall of the Main Uralian fault. The Uralian orogenic evolution can be subdivided into three deformation stages with differently oriented stress regimes. Tectonic convergence started in the Late Devonian with ophiolite obduction, tectonic accretion of basin and slope units and early flysch deposits (Zilair flysch). The accretionary complex prograded from the SE to the NW. Continuous NW/SE-directed convergence resulted finally in the formation of an early orogenic wedge thrusting the Cadomian basement complex onto the East European platform. The main tectonic shortening was connected with these two stages and, although not well constrained, appears to be of Late Devonian to Carboniferous age. In the Permian a final stage of E–W compression is observed throughout the SW Urals. In the west the fold-and-thrust-belt prograded to the west with reactivation of former extensional structures and minor shortening. In the east this phase was related to intense back thrusting. The East European platform was subducted beneath the Magnitogorsk magmatic arc during the Late Paleozoic collision. The thick and cold East European platform reacted as a stable rigid block which resulted in a narrow zone of intense crustal shortening, tectonic stacking and high strain at its eastern margin. Whereas the first orogenic wedge is of thick-skinned type with the involvement of crystalline basement, even the later west-directed wedge is not typically thin-skinned as the depth of the basal detachment appears below 15 km and the involvement of Archean basement can be assumed.     

Key principles of constructing probabilistic statistical ionosphere models for the radiowave propagation problems

It is demonstrated that it is required to create probabilistic statistical models of the ionosphere for calculating radio propagation in a wide frequency range. This, in fact, presents a new type of ionospheric modeling. These models are classified into pure statistical and deterministic-stochastic. We describe the key principles of building such models, present some examples of their construction, and discuss some difficulties arising from them.     

On the covering of a Hill’s region by solutions in the restricted three-body problem

We consider two classical celestial-mechanical systems: the planar restricted circular three-body problem and its simplification, the Hill’s problem. Numerical and analytical analyses of the covering of a Hill’s region by solutions starting with zero velocity at its boundary are presented. We show that, in all considered cases, there always exists an area inside a Hill’s region that is uncovered by the solutions.