Effect of the cryolithic zone electrical properties on the medium-frequency surface wave at high latitudes

Result of the measurements of the cryolithic zone electrical properties by the radio impedance sounding method are presented. The surface impedance and geoelectric section of the Arctic permafrost have been determined. The experiments have been performed near Cherskii in the continental zone. The surface wave attenuation function is considered. The accuracy of the surface wave field calculations at high latitudes has been estimated based on the local electrical characteristics of the underlying cryogenic medium. The effect of the Arctic Ocean on the operating zone of navigation and communication facilities in the kilometer wave band has been experimentally estimated.     

Instantaneous radio spectra of giant pulses from the crab pulsar from decimeter to decameter wavelengths

The results of simultaneous multifrequency observations of giant radio pulses from the Crab pulsar, PSR B0531+21, at 23, 111, and 600 MHz are presented and analyzed. Giant pulses were detected at a frequency as low as 23 MHz for the first time. Of the 45 giant pulses detected at 23 MHz, 12 were identified with counterparts observed simultaneously at 600 MHz. Of the 128 giant pulses detected at 111 MHz, 21 were identified with counterparts observed simultaneously at 600 MHz. The spectral indices for the power-law frequency dependence of the giant-pulse energies are from ?3.1 to ?1.6. The mean spectral index is ?2.7 ± 0.1 and is the same for both frequency combinations (600–111 MHz and 600–23 MHz). The large scatter in the spectral indices of the individual pulses and the large number of unidentified giant pulses suggest that the spectra of the individual giant pulses do not actually follow a simple power law. The observed shapes of the giant pulses at all three frequencies are determined by scattering on interstellar plasma inhomogeneities. The scatter-broadening of the pulses and its frequency dependence were determined as τ _sc = 20(ν/100)^?3.5±0.1 ms, where frequency ν is in MHz.     

Evolution of a filament due to magnetic-field variations in a complex active region

The complex active region NOAA 9672 is studied when it was near the central meridian, from October 21–26, 2001. At that time, there was an emergence of new magnetic flux, with the ongoing formation of a filament. The dynamics of the magnetic field are studied in order to search for their possible manifestations in the filament structure, using SOHO MDI magnetograms, SOHO EIT and TRACE filtergrams in the 171 Å line, and Hα filtergrams available via the Internet. Our earlier conclusion that filaments form at the boundaries of supergranules near polarity-inversion lines is confirmed. The conclusion of Chae that sinistral filaments have positive magnetic helicity is also confirmed. New information about magnetic-field decay processes is obtained. The direction of motion of the magnetic poles and their relative positions suggest that the axial field of a filament forms as a result of either reconnection of cancelling magnetic poles, or emergence of horizontal magnetic-flux tubes.     

Paleozoic rocks in infrastructure of the metamorphic core, the Greater Caucasus Main Range zone

Granitoid orthogneisses and migmatites are widespread in the lower, deeply metamorphosed gneiss-migmatite complex of the pre-Alpine basement (infrastructure) exposed within northern part of the Greater Caucasus Main Range zone. Like the other rocks of the complex, they have been traditionally attributed to the Proterozoic, but the U-Pb dating revealed the Late Paleozoic age of migmatites and Devonian age of orthogneiss protolith. Bodies of blastomylonitic apogranite gneisses, which are confined to boundary between gneiss-migmatite complex and overlying Makera Complex of supracrustal rocks, turned out to be of the Late Paleozoic age as well. The dating results suggest synchronism and, apparently, genetic interrelations between the high-T/low-P metamorphism and granite formation in the Main Range zone of the Greater Caucasus.     

Radio occultation probing of the turbulent circumsolar plasma by pulsar pulses at small elongations

The possibility of using the occultation of a pulsar by the solar corona for diagnostics of the magnitude of coronal electron-density inhomogeneities is analyzed. Coronal probing at small elongations is considered, when a ground-based receiver can be in the vicinity of the caustic surface due to the regular refraction of the pulsar radio emission in the circumsolar plasma.     

Protoliths of the metamorphic rocks of the Fedorov Complex, Aldan shield: Character, age, and geodynamic environments of origin

Geochemical data indicate that the protoliths of the overwhelming majority of the metamorphic rocks composing the Fedorov Complex in the Aldan granulite megacomplex were volcanic rocks of three groups, which occur in different proportions in the complex: (i) volumetrically predominant (no less than 90%) continuous differentiated island-arc basalt-andesite-dacite-rhyolite series, (ii) within-plate basalts, whose composition was similar to that of low-Ti traps, and (iii) basalts of composition similar to that of continentalrift basalts. The U-Pb zircon crystallization age of the metamorphosed basaltic andesites of the Fedorov Complex was estimated at 2006 ± 3 Ma, which testifies, when considered together with preexisting geochronological data, that the complex was produced during a time span of no longer than 25 m.y. A model is proposed according to which the complex was produced within the geodynamic system of the active continental margin of the Olekma-Aldan continental microplate and the Fedorov island arc.     

Pyritization of fossil mollusk shells and some problems of supergene sulfide formation

The study of specific features of the pyritization of mollusk fossil shells has provided new evidence of the relationship between the generation of hydrosulfides during the bacterial reduction of sulfates and the composition of organic matter (OM) exploited by bacteria in processes of metabolism. The OM is represented by conchiolin of the ammonite shell frustule. Interaction between the bacterial H₂S and Fe²⁺ fosters the pseudomorphous replacement of conchiolin by the colloidal iron monosulfide that is subsequently transformed into pyrite. Hydrogen sulfide and/or monosulfide migrate into diagenetic cracks and cavities formed in the clayey—carbonate matrix that fills up the interior cavity of a shell. We believe that the data reported in this communication should be taken into consideration in the study of formation constraints of vein and disseminated sulfide mineralization in sedimentary rocks during the early diagenesis and related problems of ore formation.     

Ultramafic rocks from the Markov Deep in the rift valley of the Mid-Atlantic Ridge

The paper presents materials on the composition and texture of weakly serpentinized ultrabasic rocks from the western and eastern walls of the Markov Deep (5°30.6′–5°32.4′N) in the rift valley of the Mid-Atlantic Ridge (MAR). The predominant harzburgites with protogranular and porphyroclastic textures contain two major generations of minerals: the first generation composes the bulk of the rocks and consists of Ol _89.8–90.4 + En _90.2–90.8 + Di _91.8 + Chr (Cr#32.3–36.6, Mg#67.2–70.0), while the second generation composes very thin branching veinlets and consists of PlAn _32–47 + Ol _74.3–77.1 + Opx _55.7–71.9 + Cpx _67.5 + Amph _53.7–74.2 + Ilm. The syndeformational olivine neoblasts in recrystallization zones are highly magnesian. The concentrations and covariations of major elements in the harzburgites indicate that these rocks are depleted mantle residues (the high Mg# of minerals and whole-rock samples and the low CaO, Al₂O₃, and TiO₂ concentrations) that are significantly enriched in trace HFSE and REE (Zr, Hf, Y, LREE, and all REE). The mineralogy and geochemistry of the harzburgites were formed by the interaction of mantle residues with hydrous, strongly fractionated melts that impregnated them. The mineralogical composition of veinlets in the harzburgites and the mineralogical-geochemical characteristics of the related plagiogranites and gabbronorites suggest that these plagiogranites were produced by melts residual after the crystallization of gabbronorites. The modern characteristics of the harzburgites were shaped by the following processes: (i) the partial melting of mantle material simultaneously with its subsolidus deformations, (ii) brittle-plastic deformations associated with cataclastic flow and recrystallization, and (iii) melt percolation along zones of the maximum stress relief and the interaction of this melt with the magnesian mantle residue. Original Russian Text ? G.N. Savel’eva, N.S. Bortnikov, A.A. Peyve, S.G. Skolotnev, 2006, published in Geokhimiya, 2006, No. 11, pp. 1192–1208.