Formation of kyanite–quartz veins of the Alpe Sponda,Central Alps,Switzerland: implications for Al transport during regional metamorphism

In this study, we have investigated the formation of quartz–kyanite veins of the Alpe Sponda, Central Alps, Switzerland. We have integrated field observations, fluid inclusion and stable isotope data and combined this with numerical geochemical modeling to constrain the chemical processes of aluminum transport and deposition. The estimated P–T conditions of the quartz–kyanite veins, based on conventional geothermometry (garnet–biotite, white mica solvus and quartz–kyanite oxygen isotope thermometry) and fluid inclusion data, are 550 ± 30°C at 5.0 ± 0.5 kbar. Geochemical modeling involved construction of aqueous species predominance diagrams, calculation of kyanite and quartz solubility, and reaction–path simulations. The results of the modeling demonstrate that (1) for the given chemical composition of the vein-forming fluids mixed Al–Si aqueous species are dominant in transporting Al, and that (2) fluid cooling along a small temperature gradient coupled with a pH decrease is able to explain the precipitation of the quartz–kyanite assemblages in the proportions that are observed in the Alpe Sponda veins. We conclude that sufficient amounts of Al can be transported in typical medium- to high-grade regional metamorphic fluids and that immobile behavior of Al is not very likely in advection–dominanted fluid–rock systems in the upper and middle crust.     

Factors influencing long range dependence in streamflow of European rivers

Investigating long range dependence of river flows, especially in connection with various climate and storage related factors, is important in order to improve stochastic models for long range dependence and in order to understand deterministic and stochastic variability in long‐term behaviour of streamflow. Long range dependence expressed by the Hurst coefficient H is estimated for 39 (deseasonalized) mean daily runoff time series in Europe of at least 59 years using five estimators (rescaled range, regression on periodogram, Whittle, aggregated variances, and least squares based on variance). All methods yield estimates of H > 0.5 for all data sets. The results from the different estimators are significantly positively correlated for all pairs of methods indicating consistency of the methods used. Correlations between H and various catchment attributes are also analysed. H is strongly positively correlated with catchment area. Apparently, increasing storage with catchment area translates into increasing long range dependence. H is also positively correlated with mean discharge and air temperature and negatively correlated with the mean specific discharge and the seasonality index (maximum Pardé coefficient). No significant correlation is found between the Hurst coefficient and the length of the analyzed time series. The correlations are interpreted in terms of snow processes and catchment wetness. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of instrumental observations of the Jesenice meteorite fall on April 9, 2009

Abstract– We report an analysis of instrumental observations of a very bright fireball which terminated with a meteorite fall near the town of Jesenice in Slovenia on April 9, 2009, at 0h59m46s UT. The fireball designated EN090409 was recorded photographically and photoelectrically by two southern stations of the Czech part of the European Fireball Network (EN). Simultaneously, a part of the luminous trajectory was also captured by two all‐sky CCD systems and one video camera of the Slovenian meteor network. In addition to these optical recordings, the sonic booms produced by the Jesenice fireball were detected at 16 seismic stations located within 150 km of the trajectory. From all these records, we reconstructed the fireball’s atmospheric trajectory, basic geophysical data, the possible impact area, and the original heliocentric orbit of the meteoroid. Using a detailed fireball light curve, we modeled the atmospheric fragmentation of the meteoroid. Both the atmospheric behavior and the heliocentric orbit proved to be quite normal in comparison with other observed meteorite falls. The Jesenice orbit is markedly different from the P?íbram and Neuschwanstein orbital meteorite pair, which fell on similar dates (April 7, 1959, and April 6, 2002, respectively). Three meteorites with a total weight of 3.6 kg (until April 2010) were found in a high mountain area near the town of Jesenice. They are classified as L6 ordinary chondrites ( Bischoff et al. 2010 ).     

Analysis of processes leading to localized electron enhancements in the outer radiation belt

New information obtained about >500 keV electron intensity enhancements, which have been observed intermittently close to the outer edge of the electron radiation belt, is used in conjunction with an earlier statistical study by Brown and Stone (1972) to investigate processes which could lead to such structures. The enhancements are typically of ～20 sec duration and occur in a very narrow invariant latitude band, maximally 2° wide. The intensity increase relative to the “normal” background level is up to a factor 10, and the “spike” frequency of occurrence is strongly local time dependent, with more spikes observed in the night and dusk-noon sectors than in the noon-dawn sector. The processes investigated quantitatively are distortions of the magnetospheric topology in the equatorial region, wave-particle interactions and the effects of ionospheric currents. It is shown that the various processes which contribute to equatorial field disturbances can explain the observations.     

Dissolution rates of pure methane hydrate and carbon-dioxide hydrate in undersaturated seawater at 1000-m depth

To help constrain models involving the chemical stability and lifetime of gas clathrate hydrates exposed at the seafloor, dissolution rates of pure methane and carbon-dioxide hydrates were measured directly on the seafloor within the nominal pressure-temperature (P/T) range of the gas hydrate stability zone. Other natural boundary conditions included variable flow velocity and undersaturation of seawater with respect to the hydrate-forming species. Four cylindrical test specimens of pure, polycrystalline CH₄ and CO₂ hydrate were grown and fully compacted in the laboratory, then transferred by pressure vessel to the seafloor (1028 m depth), exposed to the deep ocean environment, and monitored for 27 hours using time-lapse and HDTV cameras. Video analysis showed diameter reductions at rates between 0.94 and 1.20 μm/s and between 9.0 and 10.6 · 10⁻² μm/s for the CO₂ and CH₄ hydrates, respectively, corresponding to dissolution rates of 4.15 ± 0.5 mmol CO₂/m²s and 0.37 ± 0.03 mmol CH₄/m²s. The ratio of the dissolution rates fits a diffusive boundary layer model that incorporates relative gas solubilities appropriate to the field site, which implies that the kinetics of the dissolution of both hydrates is diffusion-controlled. The observed dissolution of several mm (CH₄) or tens of mm (CO₂) of hydrate from the sample surfaces per day has major implications for estimating the longevity of natural gas hydrate outcrops as well as for the possible roles of CO₂ hydrates in marine carbon sequestration strategies.     

Paleomagnetic investigations of the tertiary and quaternary rocks: IX The pliocene of southeast Sicily and some Cretaceous rocks from Capo Passero

A sampling of Plio-Pleistocene and Upper Cretaceous basalts in SE Sicily yielded the following informationAssuming that the Cretaceous direction is reversed, the confidence oval for the virtual pole overlaps that for the Cretaceous pole of Africa determined from the Mlanje Syenite byMcElhinny et al. If SE Sicily was attached to Africa when these Upper Cretaceous lavas erupted, this result implies that extensive relative movement between the two is not likely to have occurred subsequently.

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Zusammenfassung Die Aufsammlung und Untersuchung plio-pleistozäner und oberkretazischer Basalte in SE-Sizilien ergab die folgende paläomagnetische InformationUnter der Annahme einer inversen kretazischen Feld-Richtung überlappt der Konfidenzkreis des virtuellen Pols den kretazischen magnetischen Pol für Afrika, der vonMcElhinny et al. an den Gesteinen des Mlanje Syenites bestimmt wurde.Wenn SE-Sizilien zur Zeit der Extrusion dieser oberkretazischen Laven an Afrika angeheftet war, dann besagt dieses Ergebnis, da\ eine extensive relative Bewegung zwischen diesen beiden schwerlich nacheinander stattgefunden hat.

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Résumé La compilation et l'analyse de basaltes d'âge plio-pleistocène et crétacique supérieur dans la SE-Sicile fournit l'information paléomagnétique suivanteDans l'acceptation d'un champ inversé au Crétacique, le cercle de confidence du pÔle virtuel recouvre le pÔle magnétique crétacique pour l'Afrique, tel queMcElhinny et al. l'ont déduit des roches de la Syénite de Mlanje. Si l'on rattache le SE de la Sicile à l'Afrique au moment de l'éruption de ces laves du Crétacique supérieur, ce résultat signifie qu'il est peu probable qu'un mouvement relatif extensif ait eu lieu entre les deux.

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