Reflection of the solar wind parameters in the CR geomagnetic cutoff rigidity before a strong magnetic storm in November 2003

The time variations in the CR geomagnetic cutoff rigidity and their relation to the interplanetary parameters and the Dst index during a strong magnetic storm of November 18–24, 2003, have been analyzed. The Tsyganenko (Ts03) model of a strongly disturbed magnetosphere [Tsyganenko, 2002a, 2002b; Tsyganenko et al., 2003] have been used to calculate effective geomagnetic thresholds with the help of the method for tracing CR particle trajectories in the magnetospheric magnetic field. The geomagnetic thresholds have been calculated using the method of global spectrographic survey (GSS), based on the data from the global network of CR stations, and the results have been compared with the effective geomagnetic cutoff rigidities. The daily anisotropy of effective geomagnetic thresholds during the Dst variation minimum have been estimated. The relation of the theoretical and experimental geomagnetic thresholds, obtained using the GSS method, to the interplanetary parameters and Dst variation is analyzed. The Dst variations, IMF B _z , and solar wind density are most clearly defined in the geomagnetic thresholds during this storm. The correlation between B _y and experimental geomagnetic thresholds is higher than such a correlation between this parameter and theoretical thresholds by a factor 2–3, which suggests that a real dawn-dusk asymmetry during this storm was stronger than such an asymmetry represented by the Ts03 model.     

Carbonatite magmatism of the southern Siberian Craton 1 Ga ago: Evidence for the beginning of breakup of Laurasia in the early Neoproterozoic

Apatite and biotite from dolomite?ankerite and calcite?dolomite carbonatite dikes emplaced into the Paleoproterozoic metamorphic rock complex in the southern part of the Siberian Craton are dated by the U–Pb (LA-ICP-MS) and ⁴⁰Ar–³⁹Ar methods, respectively. Proceeding from the lower intercept of discordia with concordia, the age of apatite from calcite?dolomite carbonatite is estimated to be 972 ± 21 Ma and that for apatite from dolomite?ankerite carbonatite, as 929 ± 37 Ma. Values derived from their upper intercept have no geological sense. The ages obtained for biotite by the ⁴⁰Ar–³⁹Ar method are 965 ± 9 and 975 ± 14 Ma. It means that the formation of carbonatites reflects the earliest phases of the Neoproterozoic stage in extension of the continental lithosphere.     

Natural monocrystalline α-carbyne

Doklady Earth Sciences -     

Mineralogical and geochemical features of graphitized rocks in the Chernorudka-Barakchin Tectonic Zone

The morphological and structural characteristics of graphite from the deep Chernorudka-Barakchin Fault Zone, Western Baikal region, are described. A complex of mineralogical investigations shows that graphite varieties of the Baikal region are characterized by a perfect structure. The most crystallographically regular samples are composed only of sp ²-carbon, whereas the virtually amorphous varieties are formed by sp ²-and sp ³-carbons as well. The characteristic features of the graphite varieties distinguish them from carbonaceous matter of metamorphic rocks. High concentrations of Co, Ni, Cr, Cu, Ti, Zn, Sc, V, S, Nb, Zr, Sr, Ba, Y, Nd, and La were detected while analyzing the microcomponent composition of the graphitized rocks. The majority of these elements are contained in microinclusions hosted in graphite. The elevated noble metal contents were established in graphitized metasomatic rocks, granitoids, and particularly, in graphite concentrates extracted from these rocks. Sulfides, native metals, and intermetallic compounds were detected in microinclusions. It is suggested that the inflow of reduced high-carbonaceous fluids was responsible for the transfer of chemical elements.     

Radial–Concentric Structures in the Basement of an Ancient Craton and Formation Conditions of Hydrocarbon Kitchens: Reconstruction from Seismotectonic Data

Geotectonics - Analysis of the identification of hydrocarbon generation foci (hydrocarbon kitchens) by state-of-the-art methods has been carried out. Radial–concentric structures in the...     

Age and Melt Sources of Ultramafic Dykes and Rocks of the Bolshetagninskii Alkaline Carbonatite Massif (Urik-Iya Graben,SW Margin of the Siberian Craton)

Doklady Earth Sciences - The age of rocks of the Bolshetagninskii ijolite–syenite–carbonatite massif and ultramafic dykes within the Urik-Iya Graben in the southwestern part of the...     

Ecological–Biogeochemical Monitoring of a Linden Avenue in a Megapolis

Ecological–biogeochemical monitoring of a linden avenue on Kosygin Street, Moscow, has revealed that soils at sites regarded as contaminated contain elevated Mn, Fe, Sr, and Se concentrations and lower Zn contents. Linden leaves at the assumed contaminated sites typically contain higher Cu and Fe concentrations and not as much higher Zn, As, and Cr concentrations but much lower Mn and Sr concentrations. Water leachates of soils at sites regarded as background have slightly lower pH and lower Ca, Mg, K, and Na concentrations and total mineralization. Test for phytochelatins in the leaves proved to be rather ineffective, as also were estimates of the fluctuating asymmetry of the leaf laminas. The greatest differences were detected in the degree of leaf pathology and the contents of pigments.