Discovery of an albite gneiss from the Ile de Groix (Armorican Massif, France): geochemistry and LA-ICP-MS U–Pb geochronology of its Ordovician protolith

For the first time, an albite orthogneiss has been recognised and dated within the HP–LT blueschist facies metabasites and metapelites of the Ile de Groix. It is characterised by a peraluminous composition, high LILE, Th and U contents, MORB-like HREE abundances and moderate Nb and Y values. A U–Pb age of 480.8?±?4.8?Ma was obtained by LA-ICP-MS dating of zircon and titanite. It is interpreted as the age of the magmatic emplacement during the Early Ordovician. Morphologically different zircon grains yield late Neoproterozoic ages of 546.6–647.4?Ma. Zircon and titanite U–Pb ages indicate that the felsic magmatism from the Ile de Groix is contemporaneous with the acid, pre-orogenic magmatism widely recognised in the internal zones of the Variscan belt, related to the Cambro-Ordovician continental rifting. The magmatic protolith probably inherited a specific chemical composition from a combination of orogenic, back-arc and anorogenic signatures because of partial melting of the Cadomian basement during magma emplacement. Besides, the late Devonian U–Pb age of 366?±?33?Ma obtained for titanite from a blueschist facies metapelite corresponds to the age of the HP–LT peak metamorphism.     

Vertical Patterns of Suspended Matter Characteristics Along a Coastal-basin Transect in the Western Baltic Sea

Suspended particulate matter samples were collected from the water column, the bottom nepheloid layer and the ‘ fluffy layer ’ from four stations along a coastal-basin transect in the Pomeranian Bight, western Baltic Sea. Sampling was performed nine times between October 1996 and December 1998 for various analyses, including electron probe x-ray micro analysis for detailed mineralogical investigations.Specific vertical patterns of clay mineral distributions were found. Suspended particulate matter (SPM) in the bottom nepheloid layer and the ‘ fluffy layer ’ overlying sediments was enriched in organic carbon and hydrated three layer clay minerals, whereas the non-aggregated SPM was dominated by quartz and biogenic opal. It appears that separation effects operate during aggregation of mineral particles and organic matter in repeated cycles of resuspension and settling. No clear seasonal variations in the composition of the SPM were found, in spite of high spatial and temporal variability of biological and physical variables. The results suggest that preferential incorporation, possibly aided by microbiological colonization, of hydrated three layer silicates into the organic flocs is a process that occurs under a wide range of conditions. Because aggregates sink faster than individual particles, aggregate formation led to a relative enrichment of illite and smectite in the near-bottom layers. Considering the affinity of organic contaminants and heavy metals to organic matter, the selective removal of aggregated organic matter and hydrated three-layer clay minerals from the water column and enhanced transport in the near-bottom fluffy layer may be a natural cleansing mechanism operating in the shallow waters of the bight.     

Mass and particle ‘loading’ in plasma-neutral gas interaction

Qualitative considerations of mass and particle loading in plasma-neutral gas interaction are made by the help of a one-dimensional steady model. In the case of particle loading the plasma flow behind a strong shock is accelerated as in the case of mass loading regarded by Biermannet al. (1967) whereas behind a weak shock the flow is decelerated. As an example, one-dimensional time-dependent flows with ionization of the neutral gas by Alfvén's critical velocity effect are calculated. Because of the acceleration of the subsonic flow by loading processes, the existence of a tangential discontinuity in the flow around comets seems questionable.     

Late Miocene to Pliocene stratigraphy of the Kura Basin,a subbasin of the South Caspian Basin: implications for the diachroneity of stage boundaries

Relative ages of late Cenozoic stratigraphy throughout the Caspian region are referenced to regional stages that are defined by changes in microfauna and associated extreme (>1000 m) variations in Caspian base level. However, the absolute ages of these stage boundaries may be significantly diachronous because many are based on the first occurrence of either transgressive or regressive facies, the temporal occurrence of which should depend on position within a basin. Here, we estimate the degree of diachroneity along the Akchagyl regional stage boundary within the Caspian basin system by presenting two late Miocene‐Pliocene aged measured sections, Sarica and Vashlovani, separated by 50 km and exposed within the Kura fold‐thrust belt in the interior of the Kura Basin. The Kura Basin is a western subbasin of the South Caspian Basin and the sections presented here are located >250 km from the modern Caspian coast. New U‐Pb detrital zircon ages from the Sarica section constrain the maximum depositional age for Productive Series strata, a lithostratigraphic package considered correlative with the 2–3 Myr‐long regional Eoakchagylian or Kimmerian stage that corresponds to a period of extremely low (>500 m below the modern level) Caspian base level. This new maximum depositional age from the Productive Series at Sarica of 2.5 ± 0.2 Ma indicates that the regionally extensive Akchagyl transgression, which ended the deposition of the Productive Series near the Caspian coast at 3.2 Ma, may have appeared a minimum of 0.5 Myr later in the northern interior of the Kura Basin than at the modern Caspian Sea coast. The results of this work have important implications for the tectonic and stratigraphic history of the region, suggesting that the initiation of the Plio‐Pleistocene Kura fold‐thrust belt may have not been as diachronous along strike as previously hypothesized. More generally, these results also provide a measure of the magnitude of diachroneity possible along sequence boundaries, particularly in isolated basins. Comparison of accumulation rates between units in the interior of the Kura subbasin and the South Caspian main basin suggest that extremely large variations in these rates within low‐stand deposits may be important in identifying the presence of subbasins in older stratigraphic packages.     

A Database for Volatile Organic Compounds

The database for volatile organic compounds (VOC data base) was created with the aim of providing an overview of tropospheric hydrocarbon measurements. The data base contains 202 substances, for which atmospheric and useful kinetic data such as rate coefficients, photolysis frequencies, mixing ratios, emission data and ozone formation potentials are compiled from available literature. The database file can be downloaded without charge from http://www.physchem.uni-wuppertal.de/voc-database. Registered users will be informed about the appearance of updates.     

GREGOR ‐ optical design considerations

After many years of successful work the Gregory Coudé Telescope (GCT) is going to be replaced by GREGOR. This new 1.5 m telescope is the result of design considerations which to a wide extent are based on new technologies. Special aspects of the design are presented, including measures to compensate for optical aberrations caused by instrumental and atmospheric effects (Adaptive Optics). First light is expected for the end of 2004.     

Supersoft AGNs and their relations to Galactic binaries

I review some basic results on AGN with supersoft X‐ray spectra and their relations to Galactic binaries in their soft high states. This paper is based on a talk given at the Supersoft Sources Workshop at ESTEC in May 2009. Given the length of the talk and the number of pages the review cannot be complete and is biased towards my personal view. I demonstrate that at high accretion rates supersoft AGNs and Galactic binaries share steep soft X‐ray spectra, that the X‐ray variability of supersoft AGNs is more pronounced compared to Galactic binaries in their high states, that the X‐ray variability of supersoft novae and supersoft AGNs is similar, and that in Galactic binaries mostly positive time lags are seen, while negative time lags are observed in some supersoft AGN (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Asteroseismology and interferometry

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.     

Magnetic phase diagrams of Mg-, Fe-, (Cu + Ti)- and Cu-substituted braunite Mn<Superscript>2+</Superscript>Mn<Subscript>6</Subscript><Superscript>3+</Superscript>SiO<Subscript>12</Subscript>

 The magnetic behavior of the Jahn-Teller structure braunite, (Mn²⁺ _1−yM _y )(Mn³⁺ _{6− x} M_x)SiO₁₂, is strongly influenced by the incorporation of elements substituting manganese. Magnetic properties of well-defined synthetic samples were investigated in dependence on the composition. The final results are presented in magnetic phase diagrams. To derive the necessary data, ac susceptibility and magnetization of braunites with the substitutional elements M = Mg, Fe, (Cu+Ti) and Cu were measured. Whereas the antiferromagnetic ordering temperature, T _N , of pure braunite is hardly affected by the substitution of nonmagnetic Mg, it is rapidly suppressed by the substitution of magnetic atoms at the Mn positions. Typically for a concentration (x, y) ≥ 0.7 of the substituted elements, a spin glass phase occurs in the magnetic phase diagrams. Additionally, for the braunite system with Fe³⁺ substitutions, we observe in the concentration range 0.2 < x< 0.7 a double transition from the paramagnetic state, first to the antiferromagnetic state, followed by a transition to a spin glass state at lower temperatures. The unusual change of the magnetic properties with magnetic substitution at the Mn positions is attributed to the peculiar antiferromagnetic structure of braunite, which has been resolved recently. Received: 19 April 2001 / Accepted: 6 September 2001