Die Feldspate des Granites von Eisenkappel (Kärnten) und seines Randporphyres

Zusammenfassung Der Eisenkappeler Granit und sein Randporphyr wurden mineralogisch und petrographisch untersucht. Der Randporphyr und auch Übergangszonen zum Kerngranit zeigen eine Ummantelung der Alkalifeldspate mit Plagioklas-Rapakivi Textur. Genaue analytische Untersuchungen an, Alkalifeldspateinkristallen und den dazugehörigen Plagioklashüllen (bzw. den in unmittelbarer Nachbarschaft befindlichen Plagioklasen bei Proben des Kerngranits) ergaben folgende Einzelheiten: Die Alkalifeldspate sind Mikroklinperthite mit einer durchschnittlichen Triklinität von =0,50. Der Ab-Gehalt ist hoch (Kerngranit um Ab=31%, Randporphyr um Ab=38%), ebenso der An-Gehalt (durchschnittlich 3,5%). Die Plagioklase sind Oligoklase (Kerngranit um An=28%, Randporphyr um An=22%) mit einem extrem hohen Or-Gehalt (Or=4,2% bis 7,0%) und teilweise antiperthitisch entmischt. Die Zusammensetzung der Feldspate läßt auf relativ hohe Bildungstemperaturen und entsprechend niedrige Wasserdampfdrucke schließen. Die Untersuchungsergebnisse und die Entstehung der Rapakivi Textur werden diskutiert.

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Summary The granite of Eisenkappel and its marginal porphyry (Carinthia) have been investigated. The latter as well as gradations toward the central granite have alkalifeldspars manteled with plagioclase (rapakivi texture). The phenocrysts of the alkalifeldspars and their plagioclase rims and the phenocrysts of alkalifeldspar and neighbouring plagioclases in case of the central granite show the following attitudes: The alkalifeldspar are microcline perthites with an abliquity =0,50; From the central granite to the marginal porphyry the Abcontent of the alkalifeldspar increases from Ab=31–38 wight percent. The An-content is 3,5%. The An-content of the plagioclase drops in the same direction (An=28–22%). They exhibit a high Or-content (Or=4,2–7%) which is partly unmixed to antiperthite. The composition of the feldspars reflects a rather high temperature of formation and corresponding low water vapor pressure. The results and the origin of the rapakivi texture are discussed.

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Mit 6 Textabbildungen

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Herrn Prof. Dr.H. Leitmeier zum 80. Geburistag gewidmet.     

Wave-trains in the solar wind

Applying an Alfvén-Wave-Extended-QRH-approximation and the method of characteristics, we solve the equations of motion for outwardly propagating Alfvén waves analytically for three different cases of an azimuthal dependence of the background solar wind, (a) for a pure fast-slow stream configuration, (b) for the situation where the high-speed stream originates from a diverging magnetic field region, and (c) for the case of (b) and an initially decreasing density configuration (‘coronal hole’). The reaction of these waves on the background state as well as mode-mode coupling effects are neglected. These three solar wind models are discussed shortly. For the superimposed Alfvén waves we find, on an average, that there is a strong azimuthal dependence of all relevant wave parameters which, correlated with the azimuthal distributions of the solar wind variables, leads to good agreements with observations. The signature of high-speed streams and these correlations could clearly indicate solar wind streams originating from ‘coronal holes’. Contrary to the purely radial dependent solar wind, where outwardly propagating Alfvén waves are exclusively refracted towards the radial direction, we now find a refraction nearly perpendicular to the direction of the interplanetary magnetic field in the compression region and closely towards the magnetic field direction down the trailing edge and in the low-speed regime.     

What controls equatorial Atlantic winds in boreal spring?

The factors controlling equatorial Atlantic winds in boreal spring are examined using both observations and general circulation model (GCM) simulations from the coupled model intercomparison phase 5. The results show that the prevailing surface easterlies flow against the attendant pressure gradient and must therefore be maintained by other terms in the momentum budget. An important contribution comes from meridional advection of zonal momentum but the dominant contribution is the vertical transport of zonal momentum from the free troposphere to the surface. This implies that surface winds are strongly influenced by conditions in the free troposphere, chiefly pressure gradients and, to a lesser extent, meridional advection. Both factors are linked to the patterns of deep convection. Applying these findings to GCM errors indicates, that, consistent with the results of previous studies, the persistent westerly surface wind bias found in most GCMs is due mostly to precipitation errors, in particular excessive precipitation south of the equator over the ocean and deficient precipitation over equatorial South America. Free tropospheric influences also dominate the interannual variability of surface winds in boreal spring. GCM experiments with prescribed climatological sea-surface temperatures (SSTs) indicate that the free tropospheric influences are mostly associated with internal atmospheric variability. Since the surface wind anomalies in boreal spring are crucial to the development of warm SST events (Atlantic Niños), the results imply that interannual variability in the region may rely far less on coupled air–sea feedbacks than is the case in the tropical Pacific.     

Equatorial Atlantic variability and its relation to mean state biases in CMIP5

Coupled general circulation model (GCM) simulations participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analyzed with respect to their performance in the equatorial Atlantic. In terms of the mean state, 29 out of 33 models examined continue to suffer from serious biases including an annual mean zonal equatorial SST gradient whose sign is opposite to observations. Westerly surface wind biases in boreal spring play an important role in the reversed SST gradient by deepening the thermocline in the eastern equatorial Atlantic and thus reducing upwelling efficiency and SST cooling in the following months. Both magnitude and seasonal evolution of the biases are very similar to what was found previously for CMIP3 models, indicating that improvements have only been modest. The weaker than observed equatorial easterlies are also simulated by atmospheric GCMs forced with observed SST. They are related to both continental convection and the latitudinal position of the intertropical convergence zone (ITCZ). Particularly the latter has a strong influence on equatorial zonal winds in both the seasonal cycle and interannual variability. The dependence of equatorial easterlies on ITCZ latitude shows a marked asymmetry. From the equator to 15°N, the equatorial easterlies intensify approximately linearly with ITCZ latitude. When the ITCZ is south of the equator, on the other hand, the equatorial easterlies are uniformly weak. Despite serious mean state biases, several models are able to capture some aspects of the equatorial mode of interannual SST variability, including amplitude, pattern, phase locking to boreal summer, and duration of events. The latitudinal position of the boreal spring ITCZ, through its influence on equatorial surface winds, appears to play an important role in initiating warm events.     

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

In this article we discuss the importance of high‐resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi‐phase nature of the CGM in low‐redshift galaxies. High‐precision absorption‐line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi‐wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm‐hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ 6374.5 Å and [Fe XIV] λ 5302.9 Å absorption in optical QSO spectra. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Development and testing of subsurface sampling devices for the Beagle 2 lander

For planetary landing missions, the capability to acquire samples of soil and rock is of high importance whenever complex analyses (e.g. isotopic studies) on these materials are to be carried out, or when samples are to be returned to Earth. Not only surface samples are of relevance, but in recent concepts at least for Mars landing missions also subsurface samples are required. Subsurface material on Mars is believed to have been protected from the inferred oxidants at the immediate surface while also being protected from the UV influx. Therefore, there is considerable hope that in subsurface soil samples on Mars, at least organic matter delivered by meteorites may be detected, and possibly also relics of earlier simple microbial life on the planet. Likewise, samples from the inside of Martian surface rocks promise to have been protected from weathering and for the same reason they are important for organic chemistry studies. In this paper, an overview is given of the development and science of two different subsurface sampling devices for the Beagle 2 lander of ESA's Mars Express mission, being a “Mole” subsurface soil sampler and a small rock coring and sampling mechanism. Besides their sampling function, both the Mole and the Corer/Grinder will provide data on physical properties of Martian soils and rock, respectively, through the way they interact with the sampled materials. Details of the Mole and Corer/Grinder design are presented, along with results of recent tests with prototypes in the laboratory on physically analogous sample materials.     

Cathodoluminescence (CL) and electron paramagnetic resonance (EPR) studies of clay minerals

Summary ?Sheet silicates of the serpentine–kaolin-group (serpentine, kaolinite, dickite, nacrite, halloysite), the talc–pyrophyllite-group (talc, pyrophyllite), the smectite-group (montmorillonite), and illite (as a mineral of the mica-group) were investigated to obtain information concerning their cathodoluminescence behaviour. The study included analyses by cathodoluminescence (CL microscopy and spectroscopy), electron paramagnetic resonance (EPR), X-Ray diffraction (XRD), scanning electron microscopy (SEM) and trace element analysis. In general, all dioctahedral clay minerals exhibit a visible CL. Kaolinite, dickite, nacrite and pyrophyllite have a characteristic deep blue CL, whereas halloysite emission is in the greenish-blue region. On the contrary, the trioctahedral minerals (serpentine, talc) and illite do not show visible CL. The characteristic blue CL is caused by an intense emission band around 400 nm (double peak with two maxima at 375 and 410 nm). EPR measurements indicate that this blue emission can be related to radiation induced defect centres (RID), which occur as electron holes trapped on apical oxygens (Si–O centre) or located at the Al–O–Al group (Al substituting Si in the tetrahedron). Additional CL emission bands were detected at 580 nm in halloysite and kaolinite, and between 700 and 800 nm in kaolinite, dickite, nacrite and pyrophyllite. Time-resolved spectral CL measurements show typical luminescence kinetics for the different clay minerals, which enable differentiation between the various dioctahedral minerals (e.g. kaolinite and dickite), even in thin section. Received December 3, 2001; revised version accepted February 27, 2002     

Elemental and isotopic fractionation of Type B CAI-like liquids by evaporation

Vacuum evaporation experiments with Type B CAI-like starting compositions were carried out at temperatures of 1600, 1700, 1800, and 1900 °C to determine the evaporation kinetics and evaporation coefficients of silicon and magnesium as a function of temperature as well as the kinetic isotope fractionation factor for magnesium. The vacuum evaporation kinetics of silicon and magnesium are well characterized by a relation of the form J = J_oe^−E/RT with J_o = 4.17 × 10⁷ mol cm⁻² s⁻¹, E = 576 ± 36 kJ mol⁻¹ for magnesium, J_o = 3.81 × 10⁶ mol cm⁻² s⁻¹, E = 551 ± 63 kJ mol⁻¹ for silicon. These rates only apply to evaporation into vacuum whereas the actual Type B CAIs were almost certainly surrounded by a finite pressure of a hydrogen-dominated gas. A more general formulation for the evaporation kinetics of silicon and magnesium from a Type B CAI-like liquid that applies equally to vacuum and conditions of finite hydrogen pressure involves combining our determinations of the evaporation coefficients for these elements as a function of temperature (γ = γ₀e^−E/RT with γ₀ = 25.3, E = 92 ± 37 kJ mol⁻¹ for γ_Si; γ₀ = 143, E = 121 ± 53 kJ mol⁻¹ for γ_Mg) with a thermodynamic model for the saturation vapor pressures of Mg and SiO over the condensed phase. High-precision determinations of the magnesium isotopic composition of the evaporation residues from samples of different size and different evaporation temperature were made using a multicollector inductively coupled plasma mass spectrometer. The kinetic isotopic fractionation factors derived from this data set show that there is a distinct temperature effect, such that the isotopic fractionation for a given amount of magnesium evaporated is smaller at lower temperature. We did not find any significant change in the isotope fractionation factor related to sample size, which we interpret to mean that recondensation and finite chemical diffusion in the melt did not affect the isotopic fractionations. Extrapolating the magnesium kinetic isotope fractionations factors from the temperature range of our experiments to temperatures corresponding to partially molten Type B CAI compositions (1250-1400 °C) results in a value of α_Mg ≈ 0.991, which is significantly different from the commonly used value of .