An Analysis of the Content of Large Bodies in Meteor and Fireball Streams

The issue of the presence of meter- and decameter-sized bodies in meteor and fireball streams is of fundamental importance in the context of the theory of disintegration of parent bodies. Our observations, which have been carried out since 1995, indicate that such bodies are present in the Perseid, α-Capricornid, Leonid, and Coma-Berenicid meteoric streams. A catalogue is presented here for the parameters of the detected bodies. The spatial density of the meter-sized bodies is estimated based on the observational material. Within the errors, our estimates agree with the estimates based on the extrapolation of meteor and fireball data. An analysis of the observations suggests some inferences on the structure of the streams under study.__________Translated from Astronomicheskii Vestnik, Vol. 39, No. 3, 2005, pp. 263–271.Original Russian Text Copyright © 2005 by Barabanov, Smirnov.     

Sr,Nd, and Hf Isotope Composition of Rocks of the Reft Gabbro–Diorite–Tonalite Complex (Eastern Slope of the Middle Urals): Petrological and Geological Implications

This paper reports Rb–Sr and Sm–Nd isotope data on the gabbro–diorite–tonalite rock association of the Reft massif (eastern margin of the Middle Urals) and Lu–Hf isotope data on zircon populations from these rocks. In terms of Nd and Hf isotope composition, the rocks of the studied association are subdivided into two distinctly different groups. The first group consists of gabbros and diorites, as well as plagioclase granites from thin dikes and veins cutting across the gabbros. In terms of ⁴³Nd/¹⁴⁴Nd _i = 0.512518–0.512573 (ε_Nd(T) = +8.6...+9.7) and ¹⁷⁶Hf/¹⁷⁷Hf _i = 0.282961–0.283019 (ε_Hf(T) = +15.9...+17.9), these rocks are practically identical to depleted mantle. Their Nd and Hf model ages show wide variations, but in general are close to their crystallization time. The second group is represented by tonalites and quartz diorites, which compose a large body occupying over half of the massif area. These rocks are characterized by the lower values of ¹⁴³Nd/¹⁴⁴Nd _i = 0.512265–0.512388 (ε_Nd(T) = +3.7...+6.0) and ¹⁷⁶Hf/¹⁷⁷Hf _i = 0.282826–0.282870 (ε_Hf(T) = +11.1...+12.7). The T_DM values of the second group are much (two–three times) higher than their geological age (crystallization time), which indicates sufficiently long crustal residence time of their source. The initial ⁸⁷Sr/⁸⁶Sr in the rocks of both the groups varies from 0.70348 to 0.70495. This is likely explained by the different saturation of melts with fluid enriched in radiogenic Sr. The source of this fluid could be seawater that was buried in a subduction zone with oceanic sediments and released during slab dehydration. Obtained data make it possible to conclude that the formation of the studied gabbro–diorite–tonalite association is a result of spatially and temporally close magma formation processes in the crust and mantle, with insignificant contribution of differentiation of mantle basite magma.     

Early paleozoic gabbro-amphibolites in the structure of the Bureya Terrane (eastern part of the Central Asian Fold Belt): First geochronological data and tectonic position

Resulting from U-Pb geochronological study, it has been found that the gabbro-amphibolites composing the Bureya (Turan) Terrane in the eastern part of the Central Asian Fold Belt are Early Paleozoic (Early Ordovician; 455 ± 1.5 Ma) in age rather than Late Proterozoic as was believed earlier. The gabbro-amphibolites and associated metabasalts are close to tholeiites of the intraoceanic island arcs in terms of the geochemical properties. It is suggested that the tectonic block composed of these rocks was initially a seafloor fragment that divided the Bureya and Argun terranes in the Early Paleozoic and was later tectonically incorporated into the modern structure of the Bureya Terrane as a result of Late Paleozoic and Mesozoic events.     

Electrization of aerosol wetted in bipolarly ionized air

We studied the influence of the characteristics of the atmospheric ionization and physical-chemical state of condensation nuclei on the electric state of convective cells. Based on the results of experiments in an adiabatic chamber with a volume of 3200 m³, we found that, with increase in relative air humidity H from 40 to 95% with an equivalent ascent rate of 100–400 cm/s, excessive charges in amounts of about 10³ or more elementary charges per cm3 may be accumulated on the nuclei. The sign of the charge depends on the chemical composition of the hygroscopic nuclei. For instance, media with insoluble nuclei (porous silica, etc.) typically have prevailing negative charges; those with soluble nuclei (sodium chloride, etc.) are dominated by positive charges. At H = 60−90%, the electrization of soluble nuclei can be interpreted in the diffusion-kinetic models of the ion charging of aerosols. Considerable negative volume charges, which appear on insoluble hygroscopic nuclei during a rise in humidity from 40 to 70%, are explained by the structuring of surface water films, which exhibit a resemblance to negative lightweight ions. At high values (H > 90%), it is necessary to take into account the resemblance of the wetted surfaces to positive lightweight ions. We showed for the first time that, at ion formation rates of 3 and 1010 ion pairs/(cm³ s), the differences in the volume charge and wetting rate of condensation nuclei are insignificant. It is concluded that, in many meteorological situations, the first stage of electrization of the convection-derived cloud media is the ion charging of the condensation nuclei.     

Formation and properties of hydrosilicate liquids in the systems Na2O-Al2O3-SiO2-H2O and granite-Na2O-SiO2-H2O at 600°C and 1.5 kbar

In order to determine the mechanisms of formation and properties of natural hydrosilicate liquids (HSLs), which are formed during the transition from magmatic to hydrothermal mineral formation in granitic pegmatites and rare-metal granites, the formation of HSLs was experimentally studied in the Na₂O-SiO₂-H₂O, Na₂O-Al₂O₃-SiO₂-H₂O, and Na₂O-K₂O-Li₂O-Al₂O₃-SiO₂-H₂O systems at 600°C and 1.5 kbar. It was shown that the sequential extension of composition does not suppress HSL formation in the systems and expands the stability field of this phase. However, HSLs formed in extended chemical systems have different structure and properties: the addition of alumina induces some compression of the structure of the silicate framework of HSLs, which results in a decrease in water content in this phase and probably hinders the reversibility of its dehydration. It was demonstrated that HSL can be formed by the coagulation of silica present in a silica-oversaturated alkaline aqueous fluid. It was supposed that the HSL formed during this process has a finely dispersed structure. It was argued that anomalous enrichment in some elements in natural HSLs can be due to their sorption by the extensively developed surface of HSL at the moment of its formation.