The Ruiga intrusion: A typical example of a shallow-facies paleoproterozoic peridotite-gabbro-komatiite-basaltic association of the Vetreny Belt,Southeastern Fennoscandia

The Ruiga differentiated mafic-ultramafic intrusion in the northwestern part of the Vetreny Belt paleorift was described for the first time based on geological, petrological, geochronological, and geochemical data. The massif (20 km² in exposed area) is a typical example of shallow-facies peridotite-gabbro-komatiite-basalt associations and consists of three zones up to 810 m in total thickness (from bottom to top): melanogab-bronorite, peridotite, and gabbro. In spite of pervasive greenschist metamorphism, the rocks contain locally preserved primary minerals: olivine (Fo _75–86), bronzite, augite of variable composition, labradorite, and Cr-spinels. A mineral Sm-Nd isochron on olivine melanogabbronorite from the Ruiga Massif defines an age of 2.39 ± 0.05 Ga, while komatiitic basalts of the Vetreny Belt Formation were dated at 2.40–2.41 Ga (Puchtel et al., 1997). The rocks of the Ruiga intrusion and lava flows of Mt. Golets have similar major, rare-earth, and trace element composition, which suggests their derivation from a single deep-seated source. Their parent magma was presumably a high-Mg komatiitic basalt. In transitional crustal chambers, its composition was modified by olivine-controlled fractionation and crustal contamination, with the most contaminated first portions of the ejected melt. In terms of geology and geochemistry, the considered magmatic rocks of the Vetreny Belt are comparable with the Raglan Ni-PGE komatiite gabbro-peridotite complex in Canada (Naldrett, 2003).     

Structure of the Long-Living Elements of Solar Granulation

Spatial and temporal variations in thermodynamic and kinematic parameters of structural elements of solar granulation are investigated by solving the inverse nonequilibrium radiative transfer problem using the observational data from the Vacuum Tower Telescope (duration of observations 2.6 h). In the lower photosphere, we have detected long-living (with lifetime up to 1.5 h) structures—trees of fragmenting granules. They occur as a result of the division of an ascending granular flow into several fragments, which can be repeated multiple times. We have found that approximately 67% of the regions with the highest positive variations of pressure correspond to the time and place of fragmentation of granular flows; approximately 12% of the regions correspond to the approach of adjacent structures.     

A search for posteclipse brightening of Io in 1973. II

Four eclipse reappearances of Io were observed with an area-scanning photometer during the 1973 apparition of Jupiter. The results of these observations and of the ones reported in the preceding paper are discussed in the context of recent physical models for posteclipse brightening. An evaluation of the relative merits and deficiencies of all observational techniques which have been used to search for posteclipse brightening of Io leads to the conclusion that the reality of this phenomenon remains very much in doubt.     

Manifestations of miocene acid intrusive magmatism on the southern slope of the Greater Caucasus: First evidence from isotope geochronology

New isotope-geochronological data (K-Ar, Rb-Sr) provide tight geochronological constraints on the history of Late Cenozoic magmatism on the southern slope of the Greater Caucasus. Several previously unknown, rhyodacite intrusive bodies with an emplacement age of 6.9 ± 0.3 Ma (Late Miocene) are reported from the Kakheti-Lechkhumi regional fault zone in the Kvemo Svaneti-Racha area. Therefore, a pulse of acid intrusive magmatism took place in a period previously considered amagmatic in the Greater Caucasus. The petrological, geochemical, and isotopic data suggest that these rhyodacites are produced by crystallization differentiation of mantle-derived magmas, which are similar in composition to Miocene mafic lavas that erupted a few hundred thousand years later in the adjacent Central Georgian neovolcanic area. The presented results allow the conclusion that the volcanic activity within the Central Georgian neovolcanic area occurred at 7.2–6.0 Ma in two discrete pulses: (1) the emplacement of acid intrusions and (2) the eruption of trachybasaltic lavas. The emplacement of rhyodacite intrusions in the Kvemo Svaneti-Racha area marked the first pulse of young magmatism on the southern slope of the Main Caucasus range and simultaneously represented the second magmatic pulse (after granitoid magmatism of the Caucasian Mineral Waters region) within the entire Greater Caucasus.     

Contamination risk assessment of fresh groundwater using the distribution and chemical speciation of some potentially toxic elements in Calabar (southern Nigeria)

The computer program PHREEQC was used to determined the distribution, chemical speciation and mineral saturation indices in a fresh groundwater environment with limited mining activities in the adjoining areas. The aim was mainly to determine the potential risk of a coastal plain aquifer contamination by some potentially toxic elements. The results show that the elements Ba, Cd, Cu, Fe, Mn, Ni, Rb, Sr, and Zn are distributed as free metal ions. Arsenic is in the neutral form of H₃AsO₃ ^o, while three species of aluminium [Al³⁺, AlOH₂, Al(OH)₂ ⁺] dominate. The major species of uranium include UO₂CO₃, UO₂²⁺+, UO₂⁺, and UO₂OH⁺, respectively, in order of abundance. The groundwater is saturated with respect to alunite [KAl₃ (SO₄)₂ (OH)₆], basaluminite [Al₄ (OH)₁₀ SO₄], boehmite [Al(OH)], Cu metal (Cu), cuprous ferrite (CuFeO₂), diaspore [AlO(OH)], gibbsite [Al(OH)₃], goethite (FeOOH), hematite (Fe₂O₃), magnetite (Fe₃O₄) and uraninite (UO₂). Most of the species are not mobile under the prevailing pH (3.3 to 5.9) and Eh (7 to 158 mV) conditions. The mobile ones are very low in concentration and will be immobilized by precipitation of mineral phases. The study concludes that presently these species do not pose any risk to the aquifer.     

Nickel, Copper, Zinc and Cadmium Cycling with Manganese in Lake Vanda (Wright Valley, Antarctica)

Lake Vanda is a closed-basin, permanently ice-covered lake located in the Wright Valley of Antarctica. The lakes more important geochemical features include the fact that it is fed by a single glacial melt water stream for only 6–8weeks out of the year; that it has remained stratified for more than a millennium; and that, like other lakes in the region, it is remote from anthropogenic influence. These, together with the fact that it is among the least biologically productive lakes in the world, make it an ideal system for examining the transport, cycling and fate of trace metals in the aquatic environment. Like others before us, we view this lake as a natural geochemical laboratory, a flask in the desert. This paper presents the first set of closely spaced, vertical, profiles for dissolved and particulate Mn, Fe, Ni, Cu, Zn and Cd in the water column. Despite the absence of an outflow, metals in the fresh upper waters of the lake have extremely low concentrations, in the pico-molar to nano-molar range, and are partitioned largely into dissolved rather than particulate phases. Efficient metal scavenging by particles from these oxygen-rich waters is indicated. Significant increases in metal concentrations begin to appear at depth, between 57 and 60m, and these increases coincide with the onset of manganese oxide dissolution in oxic, but lower pH waters. Vertical profiles suggest that the entire suite of trace metals (Ni, Cu, Zn, and Cd) is being released from manganese oxide carrier phases. Thermodynamic analysis indicates that Mn3O4 (i.e., the mineral hausmannite) may be important in metal sequestration and recycling in the deeper waters of Lake Vanda. Manganese-reducing organisms reported by Bratina etal. (1998) are active in the zone of metal release and these could also contribute to the observed cycling.     

Assessment of Kinetic Energy of Meteoroids Detected by Satellite-Based Light Sensors

Radiation energies of bright flashes caused by disintegration of large meteoroids in the atmosphere have been measured using optical sensors on board geostationary satellites. Light curves versus time are available for some of the events. We have worked out several numerical techniques to derive the kinetic energy of the meteoroids that produced the flashes. Spectral opacities of vapor of various types of meteoroids were calculated for a wide range of possible temperatures and densities. Coefficients of conversion of kinetic energy to radiation energy were computed for chondritic and iron meteoroids 10 cm to 10 m in size using radiation–hydrodynamics numerical simulations. Luminous efficiency increases with body size and initial velocity. Some analytical approximations are presented for average conversion coefficients for irons and H-chondrites. A mean value of this coefficient for large meteoroids (1–10 m in size) is about 5–10%. The theory was tested by analyzing the light curves of several events in detail.Kinetic energies of impactors and energy–frequency distribution of 51 bolides, detected during 22 months of systematic observations in 1994–1996, are determined using theoretical values of luminous efficiencies and heat-transfer coefficients. The number of impacts in the energy range from 0.25 to 4 kt TNT is 25 per year and per total surface of the Earth.The energy–frequency distribution is in a rather good agreement with that derived from acoustic observations and the lunar crater record. Acoustic systems have registered one 1 Mt event in 12 years of observation. Optical systems have not detected such an event as yet due to a shorter time of observation. The probability of a 1 Mt impact was estimated by extrapolation of the observational data.     

The Geminid Meteor Stream Activity Profile

The existence of two maxima of the activity of the Geminid meteor stream and the general shape of the stream activity (rate curve) are discussed. The data of visual and radar observations are compared to the results of mathematical simulation. The distribution of the orbits of meteoroids, which are observed on the Earth, is determined from the mathematical model. This distribution cannot as yet be confirmed or disproved because of the absence of appropriate experimental data.     

Anisotropy of ionospheric irregularities determined from the amplitude of satellite signals at a single receiver

A new method of determining the anisotropy parameters of small-scale irregularities in the ionospheric F region is presented and experimental results are shown. The method is based on observations of amplitude fluctuations of radio waves transmitted by satellites flying above the F region. In practice, Russian navigational satellites are used and both the amplitude and the phase of the signal is measured on the ground level. The method determines both the field-aligned anisotropy and the field-perpendicular anisotropy and orientation of the spatial spectrum of the irregularities, assuming that the contours of constant power have an elliptic shape. A possibility of applying the method to amplitude tomography is also discussed. Using a chain of receivers on the ground level, one could locate the regions of small-scale irregularities as well as determine their relative intensities. Then the large-scale background structures could be mapped simultaneously by means of ordinary ray tomography using the phase observations, and therefore the relations of small-scale and large-scale structures could be investigated.     

Uncertainty in stage–discharge rating curves: application to Australian Hydrologic Reference Stations data

The purpose of this paper is to determine uncertainty in the gauged range of the stage–gauged discharge relationship for 622 rating curves from 171 Australian Bureau of Meteorology Hydrologic Reference streamgauging Stations (HRS). Water agencies use many methods to establish rating curves. Here we adopt a consistent method across all stations and develop rating curves based on Chebyshev polynomials, and estimate uncertainties from standard regression errors in which residuals from the polynomials are adjusted to ensure they are homoscedastic and normally distributed. Uncertainty in input water level is also taken into account. The median uncertainties in mean response of the available gauged discharge relationship at median daily discharges for the HRS dataset range from +4.5 to ?4.2% (95% confidence band) and for individual gaugings from +29 to ?22% incorporating a water level uncertainty of ±4 mm. The uncertainties estimated are consistent with values estimated in Australia and elsewhere.