Local structures of electrons with energies of hundreds of keV in the inner belt and the slot region observed from the Vernov satellite

The structure and dynamics of electron fluxes of subrelativistic energies in the range 235–300 keV at L < 4 during December 3–8, 2014, are analyzed according to the RELEC instrument onboard the Vernov satellite. Sharp changes in the parameters of the solar wind and the IMF were detected on December 6, but they did not lead to a magnetic storm. However, after the event of December 6, subrelativistic electron fluxes in the inner belt and the slot region were enhanced and structured. The dynamics of electron fluxes in the local transient bursts at L ~ 1.5–1.7 is considered in detail. It is shown that these bursts are associated with the development of the cyclotron instability in the tops of magnetic flux tubes near the inner belt maximum. The electron anisotropic index is estimated in these bursts. It is shown that in the beginning these bursts are anisotropic and that they become isotropic as the decay proceeds. The most likely chain of physical mechanisms that could lead to variations in electron fluxes of the inner belt described in this paper is presented. For the first time, the topological effects in stationary distributions of the electrons of the inner belt observed at low altitudes in the South Atlantic Anomaly region are explained.     

Stress drop in the sources of intermediate-magnitude earthquakes in northern Tien Shan

The paper is devoted to estimating the dynamical parameters of 14 earthquakes with intermediate magnitudes (energy class 11 to 14), which occurred in the Northern Tien Shan. For obtaining the estimates of these parameters, including the stress drop, which could be then applied in crustal stress reconstruction by the technique suggested by Yu.L. Rebetsky (Schmidt Institute of Physics of the Earth, Russian Academy of Sciences), we have improved the algorithms and programs for calculating the spectra of the seismograms. The updated products allow for the site responses and spectral transformations during the propagation of seismic waves through the medium (the effect of finite Q-factor). By applying the new approach to the analysis of seismograms recorded by the seismic KNET network, we calculated the radii of the sources (Brune radius), scalar seismic moment, and stress drop (release) for the studied 14 earthquakes. The analysis revealed a scatter in the source radii and stress drop even among the earthquakes that have almost identical energy classes. The stress drop by different earthquakes ranges from one to 75 bar. We have also determined the focal mechanisms and stress regime of the Earth’s crust. It is worth noting that during the considered period, strong seismic events with energy class above 14 were absent within the segment covered by the KNET stations.     

The eastern boundary of the Baikal collisional belt: Geological,geochronological, and Nd isotopic evidence

New geological. geochronological, and Nd isotopic data are reported for the rocks occurring at the interfluve of the Barguzin, Nomama, and Katera rivers, where the main structural elements of the Early Paleozoic collisional system have been established. The strike-slip and thrust Tompuda-Nomama and Barguzin boundary sutures separate the Svetlaya and the Katera zones of the Baikal-Muya Belt from the Barguzin terrigenous-carbonate terrane. The age estimates of syntectonic (prebatholithic) gneissic granite and gabbrodiorite intrusive bodies (469 ± 4 and 468 ± 8 Ma, respectively) coincide with the age of collisional events in the Ol’khon, Southwest Baikal, and Sayan regions (480–470 Ma). A linear zone with zonal metamorphism and granite-gneiss domes dated at 470 Ma is revealed in the allochthonous fold-nappe packet of the Upper Riphean Barguzin Formation. This zone of Caledonian remobilization marks the collisional front between the Riphean structural units of the Barguzin Terrane consolidated 0.60–0.55 Ga ago and the Baikal-Muya Belt. New data allow us to recognize this zone as the northeastern flank of the Baikal Collisional Belt. The Nd isotopic data for the reference igneous complexes of the collisional zone indicate that the Late Riphean juvenile crust was involved in the Ordovician remobilization in the zone of conjugation of the consolidated Baikalian structural elements at the northeastern flank of the Baikal Belt and likely was a basement of the entire Barguzin Terrane or, at least, its frontal portion. The lateral displacements of the terranes to the northeast during the Early Ordovician collision were constrained by the rigid structural framework of the Baikalides in the Muya segment of the Baikal-Muya Belt, where the Riphean blocks were involved in strike-slip faulting and the Vendian-Cambrian superimposed basin underwent deformation. Finally, it may be concluded that the Early Ordovician was an epoch of collision, complex in kinematics, between heterogeneous blocks of the continental crust: the Baikalides of the Baikal-Muya Belt and polycyclic Barguzin-Vitim Superterrane.     

Age of granitoids from the conjunction zone of the Baikal-Muya foldbelt and the Kalar metamorphic terrane

One of the key segments in the conjunction zone between the Baikal folded area of Baikalides, the Early Precambrian Aldan-Stanovoi shield, and the Barguzin-Vitim superterrane involving fragments of the Early Precambrian, Baikalian, and Paleozoic folded complexes is discussed. Within this segment, complicated tectonic contacts between the Late Riphean complexes of the Param-Shaman paleotrough zone in the Baikal-Muya foldbelt of Baikalides and Lower Precambrian complexes of the Kalar metamorphic terrane are mapped. The results of the U-Pb zircon isotopic dating (TIMS and SHRIMP-II) of gneisses-syenites from the Burgai Complex and gneissoid granites of the Drevnestanovoi Complex of the Early Precambrian age, as well as results of the Nd-isotope study of reference magmatic and stratified complexes of the region are presented. The ages of the oldest gneiss-syenites from the Burgai Complex and overlying plagiomigmatites in the conjunction zone have been established to differ by less than 1 Ma, making up 601 ± 5 Ma. Drevnestanovoi gneissoid granites in the conjunction zone are of the Late Paleozoic age (325–270 Ma). According to Nd isotopic data, the age of the source, from which Vendian gneisses-syenites and granites were melted, was established to be not older than the Riphean, and the material of the old continental crust to be the protolith of the upper Paleozoic granites. It has been inferred that the collision junction of Baikalian and Early Precambrian structures of the Baikal folded area and the Aldan-Stanovoi Shield into a single block took place 600 Ma ago.     

The uranium content in Dictyonema shale of the Kaibolovo–Gostilitsy Area in the Baltic basin (Leningrad Region)

This paper reports the data on the uranium content in Dictyonema shale and phosphate rock in the Kaibolovo–Gostilitsy Area of the Baltic Basin (Leningrad Region). Specific features of the uranium ore in the studied area and stratigraphic rock sequence of the Early Ordovician Pakerort horizon are considered. A high uranium concentration in the Dictyonema shale layer has been determined, the correlation of uranium with other elements was defined, probable conditions of uranium ore genesis are described, and predicted uranium resources within the studied area are estimated.     

The first Sm–Nd isotope–geochemical data on the Paleoproterozoic age of metamorphic rocks from the crystalline basement of the Yurovsk rise (Okhotsk massif)

Rocks with Paleoproterozoic Sm–Nd model ages (T _Nd(DM) = 2096–2350 Ma) are the sources of protoliths with gneiss, amphibolite, marble, and calciphyre of Yurovsk rise. This fact makes possible estimation of the lower age boundary of the formation of the crystalline basement of Yurovsk rise as Paleoproterozoic. According to the results of Sm–Nd, U–Pb (SHRIMP), and Pb–Pb geochronological studies, two isotope provinces are distinguished within the crystalline basement of the Okhotsk massif. The Paleoarchean province occupies the territory of Kukhtui rise, in which crust-forming processes played a key role (3250–3650 Ma). The Paleoproterozoic province includes Yurovsk rise, in which the major stages of crust formation have an age of 1900–2350 Ma.     

Geochemical peculiarities and sources of Late Paleozoic high-K and ultrapotassic syenite of the Synnyr and Tas massifs (eastern Siberia)

Geochemical and Sm–Nd isotope–geochemical studies of synnyrite and syenite from the Synnyr massif and high-K syenite from the Tas massif of the Late Paleozoic (eastern Siberia) corresponding to one of the largest provinces of high-K and ultrapotassic magmatism worldwide are performed. It is shown that their formation was controlled by transformation of the Precambrian continental crust of the Siberian Craton and Central Asian Mobile Belt under the influence of the Siberian mantle plume.     

Migration of lead in non-metamict zircon

The problem of activation energy calculations of lead loss from zircon and the determination of the lead diffusion coefficient in zircon based on the kinetics of diffusion is dealt with. The experimental technique for the evaluation of the diffusion parameters used in this study is thermal ionization mass-spectrometry (ThIMS). The results of experiments on the kinetics of lead loss from several zircons under linear heating, step heating and isothermal heating regimes are considered. The study of effects of grain size on the kinetics of lead loss is performed under all regimes. A comparison of various mechanisms of lead diffusion in zircon is also made. The experimental results may be much better explained by the principles of volume diffusion than by those of first-order reactions. The values of activation energies calculated from volume diffusion are in the range 7.8 to 9.5 eV for crystalline zircons. The suitability of ThIMS technique for lead migration studies is considered.     

The nature of the basement in the Archaean Dharwar craton of southern India and the age of the Peninsular Gneiss

The Archaean Peninsular Gneiss of southern India is considered by a number of workers to be the basement upon which the Dharwar supracrustal rocks were deposited. However, the Peninsular Gneiss in its present state is a composite gneiss formed by synkinematic migmatization during successive episodes of folding (DhF₁, DhF_1a and DhF₂) that affected the Dharwar supracrustal rocks. An even earlier phase of migmatization and deformation (DhF_*) is evident from relict fabrics in small enclaves of gneissic tonalites and amphibolites within the Peninsular Gneiss. We consider these enclaves to represent the original basement for the Dharwar supracrustal rocks. Tonalitic pebbles in conglomerates of the Dharwar Supergroup confirm the inference that the supracrustal rocks were deposited on a gneissic basement. Whole rock Rb-Sr ages of gneisses showing only the DhF₁ structures fall in the range of 3100–3200 Ma. Where the later deformation (DhF₂) has been associated with considerable recrystallization, the Rb-Sr ages are between 2500 Ma and 2700 Ma. Significantly, a new Rb-Sr analysis of tonalitic gneiss pebbles in the Kaldurga conglomerate of the Dharwar sequence is consistent with an age of ～2500 Ma and not that of 3300 Ma reported earlier by Venkatasubramanian and Narayanaswamy (1974). Pb-Pb ages based on direct evaporation of detrital zircon grains from the metasedimentary rocks of the Dharwar sequence fall into two groups, 3300–3100 Ma, and 2800–3000 Ma. Stratigraphic, structural, textural and geochronologic data, therefore, indicate that the Peninsular Gneiss of the Dharwar craton evolved over a protracted period of time ranging from > 3300 Ma to 2500 Ma.     

Spatial and Temporal Characteristics of Subrelativistic Electron Fluxes in the Near-Earth Space from the Vernov Satellite Data

Geomagnetism and Aeronomy - The spatial distribution and dynamics of subrelativistic electron fluxes (from tens to hundreds of keV) were studied in a space experiment onboard the Vernov satellite....