Cosmogenic radionuclides and mineralogical properties of the Chelyabinsk (LL5) meteorite: What do we learn about the meteoroid?          下载免费PDF全文

Pavel P. Povinec  Matthias Laubenstein  A. J. Timothy Jull  Ludovic Ferrière  Franz Brandstätter  Ivan Sýkora  Jozef Masarik  Juraj Beňo  Andrej Kováčik  Dan Topa  Christian Koeberl 《Meteoritics & planetary science》2015,50(2):273-286

On February 15, 2013, after the observation of a brilliant fireball and a spectacular airburst over the southern Ural region (Russia), thousands of stones fell and were rapidly recovered, bringing some extremely fresh material for scientific investigations. We undertook a multidisciplinary study of a dozen stones of the Chelyabinsk meteorite, including petrographic and microprobe investigations to unravel intrinsic characteristics of this meteorite. We also study the short and long‐lived cosmogenic radionuclides to characterize the initial meteoroid size and exposure age. Petrographic observations, as well as the mineral compositions obtained by electron microprobe analyses, allow us to confirm the classification of the Chelyabinsk meteorite as an LL5 chondrite. The fragments studied, a few of which are impact melt rocks, contain abundant shock melt veins and melt pockets. It is likely that the catastrophic explosion and fragmentation of the Chelyabinsk meteoroid into thousands of stones was in part determined by the initial state of the meteoroid. The radionuclide results obtained show a wide range of concentrations of ¹⁴C, ²²Na, ²⁶Al, ⁵⁴Mn, ⁵⁷Co, ⁵⁸Co, and ⁶⁰Co, which indicate that the pre‐atmospheric object had a radius >5 m, consistent with other size estimates based on the magnitude of the airburst caused by the atmospheric entry and breakup of the Chelyabinsk meteoroid. Considering the observed ²⁶Al activities of the investigated samples, Monte Carlo simulations, and taking into account the ²⁶Al half‐life (0.717 Myr), the cosmic‐ray exposure age of the Chelyabinsk meteorite is estimated to be 1.2 ± 0.2 Myr. In contrast to the other radionuclides, ¹⁴C showed a very large range only consistent with most samples having been exposed to anthropogenic sources of ¹⁴C, which we associate with radioactive contamination of the Chelyabinsk region by past nuclear accidents and waste disposal, which has also been confirmed by elevated levels of anthropogenic ¹³⁷Cs and primordial ⁴⁰K in some of the Chelyabinsk fragments.  相似文献   

Some relations between co-ordinate errors and the ellipse of errors     

Juraj Šütti 《Studia Geophysica et Geodaetica》1967,11(4):456-459

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Multivariate Interpolation of Precipitation Using Regularized Spline with Tension   总被引：9，自引：0，他引：9  

Jaroslav Hofierka  Juraj Parajka  Helena Mitasova  & Lubos Mitas 《Transactions in GIS》2002,6(2):135-150

Regularized Spline with Tension (RST) is an accurate, flexible and efficient method for multivariate interpolation of scattered data. This study evaluates its capabilities to interpolate daily and annual mean precipitation in regions with complex terrain. Tension, smoothing and anisotropy parameters are optimized using the cross-validation technique. In addition, smoothing and rescaling of the third variable (elevation) is used to minimize the predictive error. The approach is applied to data sets from Switzerland and Slovakia and interpolation accuracy is compared to the results obtained by several other methods, expert-drawn maps and measured runoff. The results demonstrate that RST performs as well or better than the methods tested in the literature. The incorporation of terrain improves the spatial model of precipitation in terms of its predictive error, spatial pattern and water balance.  相似文献   

The formation, structure, and ageing of As-rich hydrous ferric oxide at the abandoned Sb deposit Pezinok (Slovakia)     

Juraj Majzlan  Bronislava Lalinská  L’ubomír Jurkovi?  Jörg Göttlicher 《Geochimica et cosmochimica acta》2007,71(17):4206-4220

The abandoned Sb deposit Pezinok in Slovakia is a significant source of As and Sb pollution that can be traced in the upper horizons of soils kilometers downstream. The source of the metalloids are two tailing impoundments which hold ∼380,000 m³ of mining waste. The tailings and the discharged water have circumneutral pH values (7.0 ± 0.6) because the acidity generated by the decomposition of the primary sulfides (pyrite, FeS₂; arsenopyrite, FeAsS; berthierite, FeSb₂S₄) is rapidly neutralized by the abundant carbonates. The weathering rims on the primary sulfides are iron oxides which act as very efficient scavengers of As and Sb (with up to 19.2 wt% As and 23.7 wt% Sb). In-situ μ-XANES experiments indicate that As in the weathering rims is fully oxidized (As⁵⁺). The pore solutions in the impoundment body contain up to 81 ppm As and 2.5 ppm Sb. Once these solutions are discharged from the impoundments, they precipitate or deposit masses of As-rich hydrous ferric oxide (As-HFO) with up to 28.3 wt% As₂O₅ and 2.7 wt% Sb. All As-HFO samples are amorphous to X-rays. They contain Fe and As in their highest oxidation state and in octahedral and tetrahedral coordination, respectively, as suggested by XANES and EXAFS studies on Fe K and As K edges. The iron octahedra in the As-HFO share edges to form short single chains and the chains polymerize by sharing edges or corners with the adjacent units. The arsenate ions attach to the chains in a bidentate-binuclear and monodentate fashion. In addition, hydrogen-bonded complexes may exist to satisfy the bonding requirements of all oxygen atoms in the first coordination sphere of As⁵⁺. Structural changes in the As-HFO samples were traced by chemical analyses and Fe EXAFS spectroscopy during an ageing experiment. As the samples age, As becomes more easily leachable. EXAFS spectra show a discernible trend of increasing number of Fe-Fe pairs at a distance of 3.3-3.5 Å, that is, increasing polymerization of the iron octahedra to form larger units with fewer adsorption sites. Therefore, although ferrihydrite is an excellent material for capturing arsenic, its use as a medium for a long-term storage of As has to be considered with a great caution because it will tend to release arsenic as it ages.  相似文献   

Enthalpy of water adsorption and surface enthalpy of lepidocrocite (γ-FeOOH)     

Juraj Majzlan  Lena Mazeina 《Geochimica et cosmochimica acta》2007,71(3):615-623

Lepidocrocite (γ-FeOOH) appears to be thermodynamically metastable with respect to goethite (α-FeOOH) and yet the former phase forms and persists both in nature and laboratory. Here we show that the thermodynamic factors relevant to these observations cannot be dismissed, although kinetics undoubtedly plays a significant role in the formation and preservation of metastable phases. To understand the relationships of the FeOOH polymorphs in the bulk and nanoscale, we investigated the energetics of lepidocrocite nanoparticles. We measured enthalpy of water adsorption and enthalpy of formation of lepidocrocite samples with surface area of 42-103 m²/g. Having both quantities measured allowed us to calculate the surface enthalpy for a water-free surface of this phase as 0.62 ± 0.14 J/m² and the energy of a relaxed (hydrated) surface as 0.40 ± 0.16 J/m². Our measurements show that a portion of the adsorbed water (∼40% under laboratory conditions) is chemisorbed (strongly bound) with enthalpy of adsorption of −65.8 ± 2.6 kJ/mol of H₂O relative to vapor (or −21.8 ± 2.6 kJ/mol relative to liquid water). The standard enthalpy of formation from elements for a hypothetical lepidocrocite with nominal composition FeOOH and zero surface area is −552.0 ± 1.6 kJ/mol. Our results demonstrate that when considering the thermodynamic properties of iron oxides in the environment, a conclusive statement about their stability cannot be made without specifying the particle size of individual phases.  相似文献   

Calcium isotope constraints on the uptake and sources of Ca in a base-poor forest: A new concept of combining stable (δCa) and radiogenic (ε_Ca) signals     

Juraj Farkaš  Adrien Déjeant  Martin Novák 《Geochimica et cosmochimica acta》2011,75(22):7031-7046

Plant-available reserves of major base cations, Ca²⁺ and Mg²⁺, decreased markedly in soils over the past century, thus posing a potential threat to forest ecosystem health. Trees are thought to obtain dissolved Ca²⁺ ions mainly from an easily accessible soil-water reservoir also termed the ‘exchangeable cation pool’. The status of Ca reserves in this soil pool is sensitive to anthropogenic perturbations such as soil acidification induced by acid rain and/or excessive timber harvesting. Here we show that in a base-poor forest of the northeastern USA (i.e. Wachusett Mountain, Massachusetts) the ‘exchangeable Ca pool’ of deeper mineral soils has a unique isotope signature that is significantly enriched in the radiogenic ⁴⁰Ca, due to the dissolution of K-rich silicate minerals such as biotite. Using a simple isotope mass balance, and assuming that the input of Ca from biotite has a ε_Ca signature of ∼16, the results of our calculation indicate that the weathering of biotite may supply a sizeable fraction, up to 25%, of Ca²⁺ ions into the ‘exchangeable cation pool’ of deeper mineral soils. Importantly, samples of local vegetation (i.e. woody tissues of red oak) show no detectable excess of the radiogenic ⁴⁰Ca, and based on our model the upper limit of a possible biotite-derived Ca contribution in vegetation is estimated at ∼5%. We also found no evidence of the radiogenic ⁴⁰Ca signal in the samples of forest floor and the uppermost organic-rich soils (0-15 cm depth), which in turn suggest that over the long-term development of the forest and its organic matter accumulation, the vegetation growth must have also relied primarily on the non-radiogenic Ca sources. Based on our experimental data, such sources may include (i) wet atmospheric deposition, (ii) the organically-complexed Ca in topsoil horizons, and (iii) chemical weathering and/or fungal-mediated dissolution of apatite and Ca-rich plagioclase. Hence, our stable and radiogenic Ca isotope data indicate that the studied base-poor forest is able to bypass the ‘exchangeable cation pool’ of deeper (i.e. below 15 cm) mineral soils, and still manages to meet its nutritional requirements with respect to Ca. Another important implication of this study is that the organically-complexed Ca in the topsoil horizon (0-15 cm depth) has to be tightly bound to the ion exchange sites, otherwise the large radiogenic ⁴⁰Ca signatures present in the ‘exchangeable cation pool’ of deep mineral soils would be swamped by the downward gravitational flux of non-radiogenic Ca from the decaying organic matter and litterfall. Hence, the limited mobility of the organically-complexed Ca in soils and its tight biological cycling could explain the lack of a significant impact of vegetation on the Ca isotope systematics observed in large rivers.  相似文献   

Spectroscopic Observations of the 2011 Draconids Meteor Shower     

Regina Rudawska  Joe Zender  Peter Jenniskens  Jeremie Vaubaillon  Pavel Koten  Anastasios Margonis  Juraj Tóth  Jonathan McAuliffe  Detlef Koschny 《Earth, Moon, and Planets》2014,112(1-4):45-57

Some past October Draconid shower meteoroids fell apart in a spray of fragments at the end of their trajectory before slowing down, from which it was concluded that these were among the most fragile meteoroids known. In those instances, the dust could not be reliably traced to a particular return of the parent comet 21P/Giaconini-Zinner. On October 8th, 2011, Earth was predicted to transverse the 1900 A.D. dust ejecta of the comet. In 1900, the comet’s perihelion distance first moved significantly inwards to the Sun and ejection conditions could have been unusual. An airborne observing campaign was organized, with several teams contributing imaging and spectrographic cameras to study the manner in which these meteoroids released the volatile element sodium during the ablation process in the Earth’s atmosphere. IMCCE, ESA, and the SETI Institute contributed spectrographic cameras based on low-light WATEC 902H2 Ultimate, low-light LCC1, and GenII XX1332 image intensified cameras. An outburst was observed, much as predicted. Despite a lack of bright meteors, a total of 15 Draconid spectra were recorded. All show evidence of an early release of sodium. The loss of sodium was observed to coincide with the formation of a distinct wake of fragments. The observations show that 21P/Giacobini-Zinner ejected fragile meteoroids during the return in 1900. Those grains may have lost some sodium even before impacting Earth.  相似文献   

Periodicities in the green corona for the sun as a star     

Vojtech Rušin  Juraj Zverko 《Solar physics》1990,128(1):261-268

A coronal index (CI) derived from the limb observations of the 530.3 nm emission corona (green corona) over 1964–1987 was analyzed by the Fourier transform technique (FTT) to find periodicity in this layer of solar atmosphere. As expected, two pronounced periods were indicated: the rotational, about 27 d, and the activity cycle length, 11 years. Beside these there are seen other periodicities of less significancies, namely of about 5,2.2,1 and 0.5 year. The values of these periodicities in individual cycles 20 and 21 slightly differs that could be related to different activity zone depths beneath the photosphere.  相似文献   

Calcium isotope record of Phanerozoic oceans: Implications for chemical evolution of seawater and its causative mechanisms   总被引：1，自引：0，他引：1  

Juraj Farkaš  Florian Böhm  John Blenkinsop  Robert van Geldern  Silke Voigt 《Geochimica et cosmochimica acta》2007,71(21):5117-5134

A total of 280 brachiopods of Ordovician to Cretaceous age, complemented by published data from belemnites and planktonic foraminifera, are used to reconstruct the evolution of calcium isotope composition of seawater (δ^44/40Ca_SW) over the Phanerozoic. The compiled δ^44/40Ca_SW record shows a general increase from ∼1.3‰ (NIST SRM 915a) at the beginning of the Ordovician to ∼2‰ at present. Superimposed on this trend is a major long-term positive excursion from the Early Carboniferous to Early Permian as well as several short-term, mostly negative, oscillations.A numerical model of the global cycles of calcium, carbon, magnesium and strontium was used to estimate whether the recorded δ^44/40Ca_SW variations can be explained by varying magnitudes of input and output fluxes of calcium to the oceans. The model uses the record of marine ⁸⁷Sr/⁸⁶Sr ratios as proxy for seafloor spreading rates, a record of oceanic Mg/Ca ratios to estimate rates of dolomite formation, and reconstructed atmospheric CO₂, discharge and erosion rates to estimate continental weathering fluxes.The model results indicate that varying magnitudes of the calcium input and output fluxes cannot explain the observed δ^44/40Ca_SW trends, suggesting that the isotope signatures of these fluxes must also have changed. As a possible mechanism we suggest variable isotope fractionation in the sedimentary output flux controlled by the dominant mineralogy in marine carbonate deposits, i.e. the oscillating ‘calcite-aragonite seas’. The ultimate control of the calcium isotope budget of the Phanerozoic oceans appears to have been tectonic processes, specifically variable rates of oceanic crust production that modulated the hydrothermal calcium flux and the oceanic Mg/Ca ratio, which in turn controlled the dominant mineralogy of marine carbonates, hence the δ^44/40Ca_SW. As to the causes of the short-term oscillations recorded in the secular δ^44/40Ca_SW trend, we tentatively propose that these are related to variable rates of dolomite formation and/or to changing chemical composition of the riverine flux, in particular and ratios, induced by variable proportions of silicate vs. carbonate weathering rates on the continents.  相似文献   

A New Method for Low‐Temperature Decomposition of Chromites and Dichromium Trioxide using Bromic Acid Evaluated by Chromium Isotope Measurements     

Vladislav Chrastný  Jan Rohovec  Eva Čadková  Jan Pašava  Juraj Farkaš  Martin Novák 《Geostandards and Geoanalytical Research》2014,38(1):103-110

In recent years, routine application of the stable isotope determination of chromium (Cr) in environmental and health protection research has led to the search for simpler chromite decomposition techniques. As the range of Cr isotope abundance ratios in nature is very narrow, conventional chromite decomposition techniques are no longer suitable, due to the relatively high risk of contamination during laboratory procedures. We have developed a protocol for the decomposition of chromites based on oxidation by bromic acid at room temperature. The procedure takes 15 d and requires two doses of bromic acid during the reaction period (day 1 and 8), due to the limited stability of the reagent. Chromium extracted by alkaline oxidative fusion and by bromic acid decomposition yielded statistically indistinguishable δ⁵³Cr values, measured by multi‐collector inductively coupled plasma‐mass spectrometry following addition of a ⁵⁰Cr‐⁵⁴Cr double‐spike.  相似文献