Rb-Sr and U-Pb systematics of metasedimentary carbonate rocks: The Paleoproterozoic Kuetsjarvi Formation of the Pechenga Greenstone Belt, Kola Peninsula

The Rb-Sr and U-Pb systematics have been studied in the metasedimentary carbonate rocks from the Paleoproterozoic Kuetsjarvi Formation. Samples were taken from the borehole drilled in the northern zone of the Pechenga Greenstone Belt in the northwestern Kola Peninsula. The carbonate section of the formation is made up of three units (from the bottom to top): (I) dolomite (68 m), (II) calcareous-dolomite (9 m), and (III) clayey calcareous (1 m) ones. Dolomites (Mg/Ca = 0.55–0.61) from the lowermost unit I contain 70.3–111 ppm Sr. Initial ⁸⁷Sr/⁸⁶Sr ratio in them varies within 0.70560–0.70623 and characterizes the primary continental-lacustrine carbonate sediments. Calcareous dolomites (Mg/Ca = 0.39–0.59) and dolomitic limestones of units II and III (Mg/Ca = 0.02–0.36) are enriched in Sr (285–745 and 550–1750 ppm, respectively). Initial ⁸⁷Sr/⁸⁶Sr ratios in these rocks (0.70406–0.70486 and 0.70407–0.70431, respectively) fall within the range typical of the Jatulian seawater, which indicates that the carbonate sediments of two upper units were formed in an open marine basin. Study of dolomites from unit I showed that the Svecofennian metamorphism more significantly affected the U-Pb systems of carbonate rocks as compared to their Rb-Sr systems. In the ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram, most data points corresponding to the carbonate constituent of dolomites define isochron with an age of 1900 ± 25 Ma (MSWD = 0.5). The same samples define a positive correlation in the ²⁰⁸Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb plot. Since sedimentary carbonates usually do not contain Th, this correlation points to secondary enrichment of the studied dolomites in Th or thorogenic ²⁰⁸Pb. Hence, the obtained Pb-Pb dating can be regarded as the age of the Svecofennian metamorphic event. Three samples from dolomites of unit I lack any disturbance of the initial U-Th-Pb systematics, but their trend in the ²⁰⁷Pb/²⁰⁴Pb-²⁰⁶Pb/²⁰⁴Pb diagram deviates from the 1900 Ma isochron. Based on these samples, the model U-Pb premetamorphic age of the Kuetsjarvi carbonate sediments is 2075–2100 Ma. This interval is consistent with the age range of the Lomagundi-Jatulian event, which was responsible for the formation of carbonate sediments with high positive δ¹³C values.     

Minor elements in quartz from hydrothermal-metamorphic veins in the Nether Polar Ural Province

Vein quartz from the Nether Polar Ural Province was examined by atomic emission spectrometry, gas chromatography, electron paramagnetic resonance, and electron microscopy. According to atomic emission spectrometric analysis, the total concentration of Al, Fe, Mg, Ti, Ca, Na, K, and other minor elements in the quartz varies from 8 to 47 ppm. The lowest concentrations of minor elements were detected in the granulated quartz. Giant-crystalline milk-white quartz is noted for higher concentrations of minor elements, including Na, K, and Ca, because it contains gas-liquid inclusions. The fine-grained quartz contains very small mineral inclusions and is thus noted for elevated concentrations of Ca, Fe, K, Mg, and Ti. Gas chromatographic data on the gas phase separated from the quartz at its heating indicate that this phase contains H₂O, CO₂, and other components. The H₂O concentration reaches 429 ??g/g, while the CO₂ content is commonly no higher than 20 ??g/g. Gas separation is at a maximum at temperatures of 100?C600°C, when gasliquid inclusions decrepitate, as is typical, first of all, of the giant-crystalline milk-white quartz. Gas separation continues at higher temperatures (below 1000°C) but is much less intense. The electron microscopic examination of quartz grains after their acid treatment indicates that the surface of these grains is covered by caverns of various morphology and size, which were produced by the partial dissolution of the quartz and the opening of its gas-liquid and mineral inclusions occurring near the surface; the inclusions were not, however, completely removed. The crystal structure of the quartz contains minor Al, Ge, Na, Li, Ti, and Fe. The lowest concentrations of Al and Ge paramagnetic centers are typical of the granulated (recrystallized) and fine-grained quartz. The giant-crystalline quartz, including its transparent varieties, and individual quartz crystals, first of all their smoky-citrine varieties, contain higher concentrations of minor elements. In the Nether Polar Ural Province, granulated quartz is potentially promising for producing especially pure quartz concentrates. The quality of the translucent coarse-to giant-crystalline quartz, which predominates in the resources and reserves, is deteriorated by gas-liquid inclusions in it and requires deep processing of the raw minerals.     

Geochemical specifics of ongonites in the Ary-Bulak Massif, eastern Transbaikalia

A genetic model for magmatic rocks of the Ary-Bulak Massif is discussed based on a detailed geological map of the massif (prepared by the authors) and on original data of the authors on the petrography of the massif, its compositional zoning, trace-element geochemistry, physicochemical parameters of its crystallization, and melt inclusions in its minerals. The Ary-Bulak Massif was determined to be zonal, with the predominance (approximately 70% by area) of porphyritic topaz ongonites (central facies), which grade toward contacts into weakly porphyritic ongonites bearing topaz and, occasionally, fluorite (margin facies). Aphyric rocks with fluorite (inner-contact facies) occur as a stripe 50–80 m wide at the southwestern inner contact of the massif. Analysis of petrographic and geochemical data indicates that subvolcanic rocks of the Ary-Bulak Massif differ from typical elvanes (as they occur in the Cornwall province) but are similar to classic ongonites in the central and marginal facies of the massif. Rocks in the southwestern inner-contact zone are unusual high-F and high-Ca varieties, whose analogues have never been found in any rare-metal provinces with ongonites and which provide evidence of a complicated evolutionary history of the Ary-Bulak Massif. The geochemical evolution of this massif was determined to be characterized by the enrichment of the older inner-contact facies rocks in CaO, K₂O, F, and Rb, Cs, B, Ba, Sr, Sn, and Ta, whose concentrations decrease in the ongonites of the central facies. The central-facies ongonites thereby have much higher Na₂O and Li concentrations than those in the inner-contact facies rocks. It is demonstrated that the intense heating and melting of crustal material in this region at the Jurassic-Cretaceous boundary could have been induced by subalkaline basaltic magma. The chemical composition of the rocks, which is unusual for typical ongonites in, for example, high Ca and Sr concentrations, could be caused by the possible assimilation by the magma of limestones, which occur in the territory at a certain depth in the Ust’-Borzya Formation that hosts the Ary-Bulak Massif. The genesis of most rocks in the massif was controlled by the magmatic differentiation of crustal granitic magma, with the residual melts forming Li-F granites enriched in several trace elements (Li, Rb, Cs, B, Ba, Sr, etc.) and ongonites as their subvolcanic analogues.     

The MASTER-II network of robotic optical telescopes. First results

The main stages in the creation of the Russian segment of the MASTER network of robotic telescopes is described. This network is designed for studies of the prompt optical emission of gammaray bursts (GRBs; optical emission synchronous with the gamma-ray radiation) and surveys of the sky aimed at discovering uncataloged objects and photometric studies for various programs. The first results obtained by the network, during its construction and immediately after its completion in December 2010, are presented. Eighty-nine alert pointings at GRBs (in most cases, being the first ground telescopes to point at the GRBs) were made from September 2006 through July 2011. The MASTER network holds first place in the world in terms of the total number of first pointings, and currently more than half of first pointings at GRBs by ground telescopes are made by the MASTER network. Photometric light curves of GRB 091020, GRB 091127, GRB 100901A, GRB 100906A, GRB 10925A, GRB 110106A, GRB 110422A, and GRB 110530A are presented. It is especially important that prompt emission was observed for GRB 100901A and GRB 100906A, and thar GRB 091127, GRB 110422A, and GRB 110106A were observed from the first seconds in two polarizations. Very-wide-field cameras carried out synchronous observations of the prompt emission of GRB 081102, GRB 081130B, GRB 090305B, GRB 090320B, GRB 090328, and GRB 090424. Discoveries of Type Ia supernovae are ongoing (among them the brightest supernova in 2009): 2008gy, 2009nr, 2010V, and others. In all, photometry of 387 supernovae has been carried out, 43 of which were either discovered or first observed with MASTER telescopes; more than half of these are Type Ia supernovae. Photometric studies of the open clusters NGC 7129 and NGC 7142 have been conducted, leading to the discovery of 38 variable stars. Sixty-nine optical transients have been discovered.     

Spatio-temporal Evolution of Sources of Microwave and Hard X-ray Pulsations of the Solar Flare using the NoRH,RHESSI, and AIA/SDO Observation Data

This paper reports the obtained analysis data on the spatio-temporal evolution of sources of microwave and hard X-ray pulsations for the SOL2011-06-07T06:16 event based on the observation data of the RHESSI spectrometer and the Nobeyama radioheliograph. The position of the considered pulsation sources changes from one pulsation to another. The motion of the X-ray sources is predominantly longitudinal in nature in relation to the inversion line of the magnetic polarity. The obtained analysis data on the evolution of X-ray sources are in good agreement with the results of the radio image analysis. The radio brightness center at 34 GHz changes its position from one pulsation to another along the inversion line of the magnetic polarity throughout the burst. According to the AIA/SDO telescope data, the flare region images in the ultraviolet range demonstrate a well-defined eruption of the magnetic flux rope. The flare energy release can likely be triggered by the erupting magnetic flux rope; the successive interaction of different parts of it with different loops of the surrounding magnetic arcade can result in their successive “ignition” and, as a consequence, lead to the observed changes in the position of X-ray and microwave sources from one pulsation to another.     

Ozone content over the russian federation in the second quarter of 2012

The review is compiled on the basis of the results of the operation of the total ozone (TO) monitoring in the CIS and Baltic countries functioning in the operational regime at the Central Aerological Observatory (CAO). The monitoring system uses the data from the national network with M-124 filter ozonometers under methodological supervision of the Main Geophysical Observatory. The quality of the functioning of the entire system is under operational control based on the observations obtained from the OMI satellite equipment (NASA, the United States). The basic TO observation data are generalized for each month of the first quarter of 2012 and for the quarter as a whole. Some results of regular observations of surface ozone content carried out at different organizations in Russia are also considered.     

Corundum-bearing metasomatic rocks in the Central Pamirs

The Muzkol metamorphic complex in the Central Pamirs contains widespread occurrences of corundum mineralization, sometimes with gem-quality corundum. These occurrences are spatially related to zones of metasomatic alterations in calcite and dolomite marbles and crystalline schists. The calcite marbles contain corundum together with muscovite, scapolite, and biotite; the dolomite marbles contain corundum in association with biotite; and the schists bear this mineral coexisting with biotite and chlorite. All these rocks additionally contain tourmaline, apatite, rutile, and pyrite. The biotite is typically highly aluminous (up to 1.9 f.u. Al), and the scapolite is rich in the marialite end member (60–75 mol %). The crystallization parameters of corundum were estimated using mineral assemblages at T = 600–650°C, P = 4–6 kbar, X _{CO 2} = 0.2–0.5 at elevated alkalinity of the fluid. The Sr concentration in the calcite and dolomite marbles is low (345–460 and 62–110 ppm, respectively), as is typical of recrystallized sedimentary carbonates. The variations in the ⁸⁷Sr/⁸⁶Sr ratio in the calcite and dolomite marbles (0.70852–0.70999 and 0.70902–0.71021, respectively) were controlled by the introduction of radiogenic ⁸⁷Sr during the metasomatic transformations of the rocks. The isotopic-geochemical characteristics obtained for the rocks and the results of numerical simulations of the fluid-rock interactions indicate that the corundum-bearing metasomatic rocks developed after originally sedimentary Phanerozoic carbonate rocks, with the desilication of the terrigenous material contained in them. This process was a manifestation of regional alkaline metasomatism during the closing stages of Alpine metamorphism. In the course of transformations in the carbonate reservoir, the juvenile fluid flow became undersaturated with respect to silica, which was a necessary prerequisite for the formation of corundum.     

Thermal expansion of ZnSiO<Subscript>3</Subscript> high-pressure phases

Thermal expansion of ZnSiO₃ high-pressure clinopyroxene and ilmenite phases was measured in the temperature range 100–620 K by the X-ray powder diffraction method. Interpolation and extrapolation of experimental data were performed by the procedure based on the Debye-Mie-Gruneisen theory in the range from 50 to 1,500 K. Temperature dependencies of molar volumes and coefficients of bulk thermal expansion of ZnSiO₃ phases were determined.     

Application of scattered and emitted seismic waves for improving the efficiency of exploration and development of hydrocarbon fields

The success of drilling oil and gas wells is largely determined by a high hydrocarbon content and reservoir permeability at the point of penetration. Microseismic emission and scattered reflection waves are used for the reliable study of these parameters. The Seismic Location of Emission Centers and Side-View Seismic Location technologies have been developed for the observation, selection, and positioning of waves in a geological environment, which significantly extend the range of problems that are solved during seismic exploration of hydrocarbon deposits. Examples of application of these technologies in the exploration and development of hydrocarbon deposits are described.