Evolution of the blueschist and greenschist facies rocks of Sifnos,Cyclades, Greece

The metamorphism on the island of Sifnos is characterized by the Eocene development of a coherent highpressure blueschist terrane and an early Miocene greenschist facies overprint. This study documents the metamorphic evolution of the blueschist assemblages, still preserved in the northern parts of the island, and their subsequent transformation into greenschists in the central and southern parts.The oxygen isotope geothermometry is based on calibrations for quartz, pyroxenes and magnetite (Matthews et al. 1983a) augmented by revised calibrations for the minerals muscovite ( _Qz–Mu=1.55×10⁶ T _–2), epidote ( _Qz–Ep= 1.56+1.92 _ps)10⁶ T _–2), and rutile ( _Qz–Ru=4.54×10⁶ T _–2).Oxygen isotope analyses of minerals from the Blueschist unit of northern Sifnos give consistent fractionations which are independent of rock type. An average temperature of 455° C was obtained, although the scatter in temperatures deduced from the various geothermometers suggests that equilibration occurs under slightly changing physicochemical conditions. Analyses of minerals and whole rocks shows that pervasive equilibration in the presence of a common metamorphic fluid has not occurred.The minerals and whole rocks of the greenschists of central Sifnos are systematically enriched in ¹⁸O relative to the blueschist assemblages. Chemical data indicate that the greenschist overprint was accompanied by a metasomatic enrichment of Ca²⁺ and CO₂. The petrologic, isotopic and chemical evidence favour a metamorphism governed by the infiltration of ¹⁸O-CO₂ enriched aqueous solutions. It is reasonable to assume that this is connected with the Miocene magmatic activity observed throughout the Cyclades. The marbles separating the Blueschist from the Greenschist unit probably acted as barriers to fluid infiltration into the blueschists and were responsible for their preservation.The pressure of the blueschist metamorphism is estimated at 14±2 kbar, corresponding to a depth of ca. 50 km. The structural style and stratigraphy of Sifnos are suggestive of the subduction of a continental margin sequence. It is clear that the considerable tectonic depression may be associated with continental collision and underthrusting.     

Ökologie des Aluminiums

After short introductory remarks about the general chemistry of Al, some chemical methods are outlined at first to investigate the speciation of Al in solution and in solids. Speciation, precipitation and complexation are of great importance for living organisms, both for aquatic and terrestric ones. Interactions between organic substances and Al-salts or Al-containing minerals are discussed for soil, freshwater and marine sediments. In plants, especially retardation of growth by available Al, mainly by shortening of roots, is looked upon in detail, because with regard to agriculture this is an important economical factor. Starting from chemical reactions at the molecular level, physiological changes and toxicity symptoms in animal cells can be understood; the severe neuronal damage is the most striking effect. Some aspects about the exposure of workers to Al-containing dusts are added.     

Preliminary note on deerite from high-pressure metamorphic rocks of Sifnos,Greece

A new occurrence of deerite-bearing quartzites from blueschist metamorphic rocks of the Greek island of Sifnos is described, and analytical and X-ray data on deerite are presented.     

Isotopic fractionation between coexisting organic carbon—carbonate pairs in Precambrian sediments

δ¹³C_org and δ¹³C_carb values of 58 coexisting organic carbon-carbonate pairs covering the whole Precambrian have yielded means of ?24.7 ± 6.0%. [PDB] and +0.9 ± 2.7%. [PDB], respectively. Accordingly, isotopic fractionation between inorganic and organic carbon in Precambrian sediments is about the same as in geologically younger rocks (Δδ ? 25%.), a slight increase displayed by the Early Precambrian pairs (Δδ ? 28%.) being probably biassed by an over-representation in this age group of samples from one single locality (nevertheless, this value still lies within the range permitted for a possible deviation). It is reasonable to assume, therefore, that the overall isotope fractionation factor governing biological fixation of inorganic carbon has been virtually constant since some 3.3 × 10⁹ yr ago.     

Ergebnisse refraktions-seismischer Messungen im Nordteil der Geotraverse IA

Zusammenfassung Im Nordteil der Ostalpen, hauptsächlich im Gebiet zwischen Salzach und Inn, wurden bei Steinbruch-Sprengungen 11 Profile refraktions-seismisch vermessen. Weil die Geschwindigkeit seismischer Wellen im Bereich dieser Profile auch in lateraler Richtung relativ stark variiert, wurde zur Interpretation der Messungen ein vom Autor entwickeltes Computer-Programm für strahlenseismische Modellrechnungen in zweidimensional inhomogenen Medien verwendet. Für einige der Profile wurden damit Modelle abgeleitet, die als wichtigste Eigenschaft eine Unterlagerung der Kalkalpen bis mindestens 15 km von ihrem Nordrand nach Süden durch eine Schicht von maximal etwa 7 km Mächtigkeit zeigen. Diese Schicht kann nach ihrer Wellengeschwindigkeit aus Molasse und/oder Helvetikum und/oder Flysch bestehen.

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In the northern part of the Eastern Alps, mainly in the region between Salzach and Inn, 11 seismic refraction profiles were measured using quarry blasts. There are relatively big changes of seismic velocity in this area even in lateral direction, and therefore the measurements were interpreted with a ray tracing method for twodimensional inhomogeneous mediums, the computer program for which was written by the author. Thus there were found models for some of the profiles in which the most important structure is a layer of about 7 km thickness lying under the Northern Calcareous Alps and stretching at least 15 km from their northern margin southwards. From its seismic velocity this layer can consist of Molasse and/or Helveticum and/or Flysch.

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Résumé Dans la partie nord des Alpes Orientales 11 profils de seismique par réfraction ont été enrégistrés, en utilisant des explosions de carrières. La majorité des profils est située entre la Salzach et l'Inn. Les importantes variations latérales des vitesses de propagation nécessitèrent le développement d'un programme de calcul des rayons séismiques dans un milieu inhomogène à deux dimensions. L'interprétation de plusieurs des profils à l'aide de ce programme indique la présence d'une couche à faible vitesse sous les Alpes Calcaires s'étendant du bord nord des Alpes jusqu'à 15 km au moins vers le sud. L'épaisseur maximale de cette couche est environ de 7 km. Les vitesses indiquent qu'elle peut être composée de matériaux de la Molasse, des couches Helvétiques et du Flysch.

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Large are variability in climate-based soil moisture estimates and implications for remote sensing

Although the basic physical relationships between various remotely sensed signatures and soil are sound, the representativeness of pixel-averaged wetness used to interpret the remotely sensed data is often suspect and at times even doubtful. To study the affect of local variation in soil moisture on the large-area average, mean areal precipitation, temperature and modelled soil moisture in 1/4° grid cells were analyzed for a 700 km by 400 km region in the US Southern Great Plains. Variability in five years of mean daily grid cell data was investigated for 150 km² study sites, approximately corresponding in size to a satellite microwave pixel. The number of wetted grid cells and the magnitude of precipitation in grid cells within a site were highly variable. The variability of each of these factors is critical, and will not only influence mean site wetness, but also how the area will be seen from space. Analysis indicated that similar mean site precipitation values may result from numerous widely differing combinations of precipitation magnitude and watted gric cell population. Consequently, mean site moisture is also highly variable in the distribution and magnitude of the individual cell moisture values. Extreme values in several grid cells may severely bias the quadrant mean, while influencing a remote measurement much less. Although large-scale surface wetness may eventually be reliably inferred from satellite measurements, a degree of uncertainty will always exist, especially in semi-arid areas. One may be required to associate mean soil moisture with an expected distribution of wetness within a pixel.     

The Influence of NaBr/NaCl Ratio on the Br--Catalysed Production of Halogenated Radicals

The activation of Br^- and Cl^- to atomic Br and Cl in sea-spray aerosol was investigated in smog-chamber experiments. In the presence of O₃, hydrocarbons and NaCl aerosol alone no activation was observed. By adding Br^- to the aerosol, the chain reaction: Br + O₃ BrO, BrO + HO₂ HOBr, HOBr HOBr(aq), HOBr(aq) + H⁺ + Br^- Br₂ (6), HOBr(aq) + H⁺ + Cl^- BrCl (7) was verified. The step from reaction (6) to (7) is accompanied by a decrease of the Br^-/Cl^- ratio from 1/600 to less than 1/2000. In the absence of sulphate, the chain is initiated by the reaction of OH(aq) with Br^-. The pH value decreases to less than 2 during the first minutes of the experiment and later on to almost 1 (in the absence of NO_x or SO₂). This is caused by the formation of oxalic acid from alkanes and toluene. In stopped flow experiments, the reduction of Br₂ by oxalic acid was observed to occur through a two-step mechanism: HC₂O₄ ^- + Br₂ Br^- + BrC₂O₄H (k₂₂, k_-22), BrC₂O₄H Br^- + H⁺ + 2 CO₂ (23) with the following rate constants and ratios of rate constants, k ± 2: k₂₂k_-23 / k_-22 = (2.9 ± 0.3) · 10^-4 s^-1, k_-22 / k_-23 = 7000 ± ₃₀₀₀ ¹³⁰⁰⁰ M^-1, k₂₂ = 2 ±_-1 ⁴ M^-1 s^-1, and k_-23 > 0.1 s^-1, k_-22 > 600 M^-1 s^-1. Oxalic acid may be responsible for the inhibition of the chain reaction observed at the end of the experiments.     

Untersuchungen an fränkischen Verwerfungen

Zusammenfassung An vier feldgeologisch untersuchten Beispielen, dem Gräfenthaler Horst im Frankenwald, der Fränkischen Linie bei Kronach, der Kulmbacher Verwerfung bei Kirchleus und an Verwerfungszonen im Steigerwald wird gezeigt, daß die fränkischen Verwerfungen als Flächen eines zusammenhängenden Strukturfeldes angesehen werden können, das trotz seiner verschiedenartigen Erscheinungsformen im Grund- und Deckgebirge auf eine gemeinsame Ursache zurückgehen dürfte.

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Four areas in Northern Bavaria, the Gräfenthaler Horst in the Frankenwald, the Franconian Line near Kronach, the Kulmbach Fault near Kirchleus and fault zones in the Steigerwald, were investigated by different field methods. The authors are in the opinion that these Franconian faults are elements of a connecting structural region though different tectonic phenomena may be observed on the surface.

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Résumé Dans le nord de la Bavière des grands accidents tectoniques de direction NW/ SE, dont quelques-uns traversent le socle hercynien, d'autres la couverture mésozoique avoisinante, ont été étudiés par des methodes diverses. Quoique leurs caractères changent selon l'étage affectée, ces accidents sont des élements d'un seul domaine structural et ont apparement une origine commune.

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Herrn Professor Dr.Roland Brinkmann zum 70. Geburtstag gewidmet.