Advanced Production of Quasi-Definitive Magnetic Observatory Data of the INTERMAGNET Standard

Geomagnetism and Aeronomy - The system for the preparation of quasi-definitivedata of the INTERMAGNET standard is described. Unlike the final data, which was prepared no earlier than 1 year after...     

Volcano-plutonic centers: Typomorphic (source-related) mineralization-controlling structures in volcanogenic belts: Northeast Russia

The volcanic structures in the volcano-plutonic belts in East Russia and the Cenozoic volcanic belts in Kamchatka exhibit vastly different levels of erosion. The volcanic structures in the Sea-of-Okhotsk-Chukchi volcanogenic belt reflect the structure at different depths in the system-forming typomorphic ore-bearing features (volcano-plutonic centers or VPC). We consider an example, viz., the Kakhovka VPC, which is situated in the Balygychan-Sugoi depression of the Sea-of-Okhotsk-Chukchi volcanogenic belt and contains the Dukat world-class silver-gold deposit. We demonstrate the importance of volcano-plutonic centers for mineralization.     

Studying geomagnetic pulsation characteristics with the local approximation method

A local approximation method based on piecewise sinusoidal models has been proposed in order to study the frequency and amplitude characteristics of geomagnetic pulsations registered at a network of magnetic observatories. It has been established that synchronous variations in the geomagnetic pulsation frequency in the specified frequency band can be studied with the use of calculations performed according to this method. The method was used to analyze the spectral–time structure of Pc3 geomagnetic pulsations registered at the network of equatorial observatories. Local approximation variants have been formed for single-channel and multichannel cases of estimating the geomagnetic pulsation frequency and amplitude, which made it possible to decrease estimation errors via filtering with moving weighted averaging.     

Physical Characteristics of Kazan Minor Showers as Determined by Correlations with the Arecibo UHF Radar

In the northern hemisphere, the month of February is characterized by a lack of major meteor shower activity yet a number of weak minor showers are present as seen by the Kazan radar. Using the Feller transformation to obtain the distribution of true meteor velocities from the distribution of radial velocities enables the angle of incidence to be obtained for the single beam AO (Arecibo Observatory) data. Thus the loci of AO radiants become beam-centered circles on the sky and one can, with simple search routines, find where these circles intersect on radiants determined by other means. Including geocentric velocity as an additional search criterion, we have examined a set of February radiants obtained at Kazan for coincidence in position and velocity. Although some may be chance associations, only those events with probabilities of association > 0.5 have been kept. Roughly 90 of the Kazan showers have been verified in this way with mass, radius and density histograms derived from the AO results. By comparing these histograms with those of the “background” in which the minor showers are found, a qualitative scale of dynamical minor shower age can be formulated. Most of the showers are found outside the usual “apex” sporadic source areas where it is easiest to detect discrete showers with less confusion from the background.     

Skin-layer of the eruptive magnetic flux rope in large solar flares

The analysis of observations of large solar flares made it possible to propose a hypothesis on existence of a skin-layer in magnetic flux ropes of coronal mass ejections. On the assumption that the Bohm coefficient determines the diffusion of magnetic field, an estimate of the skin-layer thickness of ~10⁶ cm is obtained. According to the hypothesis, the electric field of ~0.01–0.1 V/cm, having the nonzero component along the magnetic field of flux rope, arises for ~5 min in the surface layer of the eruptive flux rope during its ejection into the upper corona. The particle acceleration by the electric field to the energies of ~100 MeV/nucleon in the skin-layer of the flux rope leads to their precipitation along field lines to footpoints of the flux rope. The skin-layer presence induces helical or oval chromospheric emission at the ends of flare ribbons. The emission may be accompanied by hard X-ray radiation and by the production of gamma-ray line at the energy of 2.223 MeV (neutron capture line in the photosphere). The magnetic reconnection in the corona leads to a shift of the skin-layer of flux rope across the magnetic field. The area of precipitation of accelerated particles at the flux-rope footpoints expands in this case from the inside outward. This effect is traced in the chromosphere and in the transient region as the expanding helical emission structures. If the emission extends to the spot, a certain fraction of accelerated particles may be reflected from the magnetic barrier (in the magnetic field of the spot). In the case of exit into the interplanetary space, these particles may be recorded in the Earth’s orbit as solar proton events.     

Yurchik Massifs in Kamchatka: Age and affiliation to magmatic associations

Petrographic and isotopic-geochemical data obtained on basic and ultrabasic rocks from the Yurchik Massif in the Ganal block of crystalline rocks in Kamchatka indicate that the distribution of major and trace elements in these rocks are analogous to those in the fractionation products of high-Al tholeiites occurring in island arcs in the eastern continental margin of Eurasia. Allivalites and dunites found as nodules in gabbronorites and gabbro of the massif are thought to be early cumulates of arc basalts. Petrographic and geochemical characteristics of the Yurchik Massif make it different from Ni-bearing Paleocene-Eocene (approximately 50 Ma) norite-cortlandite intrusions in the Sredinnyi Range of Kamchatka. U-Pb zircon and ⁴⁰Ar/³⁹Ar dates for rocks from the massif definitely testify to its younger, Early Miocene (approximately 22 Ma) age.     

Relict sulfides in terrigenous rocks of the Upper Kolyma Region

In terrigenous flysch strata of the Upper Kolyma Region in northeastern Russia, microaggregates of sulfides with spherical form are widespread. During dynamic metamorphism, spherical sulfide units were segregated into lenticular aggregates along the cleavage planes, were as seed, or were recrystallized into faceted metacrystals. Further stress on the rock sometimes led to a morphologically expressed particular dissolution of pyrite crystals along the cleavage directions, and to their depletion with admixture elements. A more substantial effect led to transformation of pyrite into pyrrotine with inclusions of chalcopyrite and Fe-Ni-Co-sulfoarsenides. Relict sulfides reflect, to a certain degree, the primary geochemical condition of the sedimentation period and its further evolution. When studying the numerous sulfidization zones, the composition of relict sulfides allows us to predict the geochemical specialization and the degree of inheritance of post-sedimentation mineralization.