Composition and Origin of Lavas from the Minami-Hiyoshi Submarine Volcano (Mariana Arc)

Doklady Earth Sciences - This work is a link in a series of studies of Late Cenozoic submarine volcanoes of the island arcs in the western part of the Pacific Ocean, representing the first detailed...     

Specific features of Lake Ladoga ecosystem under the effect of anthropogenic eutrophication

The evolution of Lake Ladoga ecosystem under the effect of a long period of critical anthropogenic phosphorus load is analyzed. It is shown that relatioships between organic matter accumulation and mineralization with considerable predominance of destruction over autochthonous production have formed in the lake by the moment when the input of P of anthropogenic origin dropped to the estimated admissible level. Studying the transformation of aquatic organic matter of tributaries in the water of Lake Ladoga suggest that a considerable portion of it, primarily, the conservative humic fraction, is now involved in turnover and serves as an additional source of C and P both for producer and destructor organisms. The processes taking place in Lake Ladoga suggest the allochthonous variant of ecosystem evolution.     

Dynamical evolution of multiple stars

We have modeled the dynamical evolution of small groups of N=3–18 stars in the framework of the gravitational N-body problem, taking into account possible coalescences of stars and the ejection of single and binary stars from the system. The distribution of states is analyzed for a time equal to 300 initial crossing times of the system. The parameters of the binaries and stable triple systems formed, as well as those of ejected single stars, are studied. In most cases, the evolution of the group results in the formation of a binary or stable triple system. The orbital eccentricities of the binaries formed are distributed according to the law f(e)=2e. As a rule, stable triple systems display pronounced hierarchy (the mean ratio of the semimajor axes of the outer and inner binaries is about 20:1). Stars are ejected with velocities from several km/s to several tens of km/s. The results of the modeling are compared with the parameters of observed wide binaries and triple systems.     

Polarization of Light Scattered by Solar System Bodies and the Aggregate Model of Dust Particles

The present study considers the dependence of characteristics of light scattering by aggregate particles on the refractive index, size, and number of spherical particles composing the aggregate, as well as on the structure and porosity of the cluster. The parameters were varied in sufficiently wide ranges to let a coherent picture of the polarimetric properties of relatively small aggregate particles emerge (the size parameter of the aggregate is less than 10). It was shown that, in the framework of the aggregate model, the behavior of polarization phase curves observed for both comets and regolith surfaces can be explained. The modeling carried out confirms that the sizes of the cometary dust particles are larger than the wavelength. However, the grains forming the cometary dust particles or the regolith (or details of the particle surface) have a size less than 0.3–0.5 m. This agrees with estimates obtained by other methods. The determining role in the formation of the polarization phase curve is played by the structure of the external layer of the clusters. The appearance of the negative branch of polarization and its shape substantially depend on the effectiveness of the interference of multiply scattered waves and on the interaction in the near field at these phase angles. Interference and interaction in the near field in turn are determined by the sizes of elementary scatterers and the structure of the ensemble. If the number of constituent particles in the aggregate is larger than several tens, its role in the formation of the negative branch of polarization is minor, while the influence on the polarization maximum position is rather substantial. The polarimetric data alone cannot provide a unique estimate of the refractive index: the brightness measurements must be invoked as well. For a more complete quantitative interpretation of the observations, the scattering matrix of aggregates comparable in size to or larger than the wavelength must be calculated in the short- and long-wavelength ranges, which still encounters serious theoretical and technical difficulties. Moreover, in order to obtain unique results, it is obvious that the spectral range of observations must be extended and that other types of measurements, such as spectroscopic ones, must also be used.     

Periodic orbits in the general three-body problem and the relationship between them

We study the regions of finite motions in the vicinity of three simple stable periodic orbits in the general problem of three equal-mass bodies with a zero angular momentum. Their distinctive feature is that one of the moving bodies periodically passes through the center of mass of the triple system. We consider the dynamical evolution of plane nonrotating triple systems for which the initial conditions are specified in such a way that one of the bodies is located at the center of mass of the triple system. The initial conditions can then be specified by three parameters: the virial coefficient k and the two angles, φ₁ and φ₂, that characterize the orientation of the velocity vectors for the bodies. We scanned the region of variation in these parameters k∈(0, 1); φ₁, φ₂∈(0, π) at steps of δk=0.01; δφ₁=δφ₂=1° and identified the regions of finite motions surrounding the periodic orbits. These regions are isolated from one another in the space of parameters (k, φ₁, φ₂). There are bridges that correspond to unstable orbits with long lifetimes between the regions. During the evolution of these metastable systems, the phase trajectory can “stick” to the vicinity of one of the periodic orbits or move from one vicinity to another. The evolution of metastable systems ends with their breakup.     

Comparative geochemistry of granitoids and metamorphic country rocks in the western Angara-Vitim batholith, western Baikal area

This paper presents materials of granitoids from the western Angara-Vitim batholith and the country gneisses and migmatites of the Talanchan Metamorphic Complex. The granitoids of the older intrusive phases of the Barguzin Complex are characterized by high dispersions in the contents of most trace element. The similarities in their trace-element signatures to those of metavolcanics of the Talanchan Group indicate that the latter could have served as a source of the granitoid melts. The increase in the K, Rb, Sn, Be, and REE contents from granitoids of the older phase of the Barguzin Complex to the main phase of this complex and further to the granites of the Zazin Complex is a result of melt fractionation which simultaneously became more uniform and acquired Eu minima. The group of calc-alkaline diorites is identical in composition to the metavolcanics and probably complements the latter. Metagabbro of normal alkalinity and synplutonic subalkali gabbro of the Oshurkov type are distinguished by composition and the relationships with the country gneisses and granitoids.     

Isotopic geochronology of the archean posttectonic association of sanukitoids, syenites, and granitoids in central Karelia

The U-Pb geochronological study (by the classic technique and on an ion microprobe) of syenites from central Karelia has established their Archean age. The age values obtained for individual massifs are 2735 ± 15 Ma for syenites from the Sjargozero Massif and 2745 ± 10 Ma for syenite from the Khizhjarvi Massif. The syenites are demonstrated to have been emplaced nearly synchronously with sanukitoid massifs in central Karelia, whose average age is 2743 ± 3 Ma (Bibikova et al., 2005). The syenites of the Sjargozero Massif and granodiorites of the Ust-Volomsky Massif were determined to have practically identical ages of 2735 and 2738 Ma, respectively, a fact also corroborating the coeval character of the syenites and granodiorites. Some zircon grains from the Sjargozero syenites contain cores with an age of about 2755 Ma, which suggests that the syenites could have been contaminated with the material of the host volcanic rocks of basaltic and andesitic composition that were metamorphosed at 2750–2760 Ma. The results of the isotopic geochronologic research indicate that the different rock groups composing the Archean postorogenic association of sanukitoids, syenites, and granitoids in central Karelia have been generated in a single stage at approximately 2740 Ma, i.e., 60–70 m.y. after the origin of the syntectonic tonalites. The zircons have elevated Th/U ratios, which is consistent with the mantle genesis of the rocks. Significant crustal contamination was identified in the most acid members of the sanukitoid series: syenites and granitoids. Our data obtained for zircons from the sanukitoids and syenites of the Karelian craton in the Baltic Shield are in good agreement with the results obtained on the sanukitoids of the Canadian Shield.     

Studies of Modern Star Catalogs Based on Photoelectric Observations of Lunar Occultations of Stars

An important area of investigation in astronomy is the relationship between fundamental and dynamical coordinate systems. Valuable material for such studies is provided by photoelectric occultation observations of stars by the Moon, which can provide high precision of detecting rapidly occurring processes and have been carried out over a long time interval. This latter feature is especially important for analyses of the stellar propermotions dynamics. A method has been developed to use photoelectric occultation observations to determine the orientation and rotational parameters of the axes of the coordinate system used for modern star catalogs relative to the coordinate axes of a highly accurate dynamical ephemeris of theMoon. A complete database of photoelectric occultation observations has been created for this purpose, containing data for 57 365 events. The combination of photoelectric occultation observations and other astronomical observations such as lunar laser-ranging data enables the highly accurate determination of parameters of the Moon’s dynamics, such as systematic errors in catalog coordinate systems, including various geodetic reference systems. The parameters of shifts and the rotation of the axes of the Hipparcos Celestial Reference Frame relative to the DE421 dynamical system are obtained. This paper is based on a talk given at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).

     

Isotope-geochemical features of Devonian rocks in the Pripyat Trough: Famennian suprasalt deposits

This work presents the results of isotope studies of the Upper Devonian (Famennian) suprasalt complex carried out with core material of exploratory borehole 71 drilled at the northwestern margin of the Pripyat Trough. Lithological features of the rocks point to a high degree of postsedimentary transformation of rocks. Significant role in these transformations was played by evaporites and related brines and the presence of hydrocarbons in the sequence. Such a combination provides insight into the behavior of isotope systems under conditions of the geochemical transformation of sedimentary material. The combined application of several isotope (δ¹³C, δ¹⁸O, δ³⁴S, and ⁸⁷Sr/⁸⁶Sr) methods made it possible to consider the complex mechanisms of compositional and isotopic transformation of rocks in the course of their lithogenetic alterations. The source material can be deduced with a high probability from the Rb-Sr systematics of the clayey component of marls.