Multistage metamorphism and deformation in high‐pressure metabasites of the northern Adula Nappe Complex (Central Alps,Switzerland)

Metabasites from the northern Adula Nappe Complex (ANC) display a complex microstructural evolution recording episodes of deformation and metamorphic re‐equilibration that were obliterated in the surrounding phengite‐bearing schists. Pre‐D1 and D1 deformation episodes are preserved as mineral inclusions within garnet cores of some amphibole‐bearing eclogites and record high‐temperature greenschist‐/amphibolite‐facies conditions. D2 produced an eclogite‐facies foliation which developed at 580 ± 70°C and 19 ± 3 kbar. D3 was a composite deformation episode which can be divided into three sub‐episodes D3m, D3a and D3b which occurred as the metamorphism evolved from post‐eclogitic high‐pressure and low‐temperature conditions through to amphibolite‐facies conditions at 590 ± 30°C and 11.7 ± 1.3 kbar. The D3 deformation episode was responsible for the development of the S3 regional‐scale foliation in the surrounding schists, whilst D4 caused the development of an S4 greenschist foliation. The composite nature of the D3 episode indicates that rocks of the northern ANC experienced a protracted post‐eclogitic structural reworking and that the current structure of this part of the Alps is a late‐Alpine feature. Copyright © 2010 John Wiley & Sons, Ltd.     

Milky Way type galaxies in a ΛCDM cosmology

We analyse a sample of 52 000 Milky Way (MW) type galaxies drawn from the publicly available galaxy catalogue of the Millennium Simulation with the aim of studying statistically the differences and similarities of their properties in comparison to our Galaxy. Model galaxies are chosen to lie in haloes with maximum circular velocities in the range 200–250 km s⁻¹ and to have bulge-to-disc ratios similar to that of the MW. We find that model MW galaxies formed 'quietly' through the accretion of cold gas and small satellite systems. Only ≈12 per cent of our model galaxies experienced a major merger during their lifetime. Most of the stars formed ' in situ ', with only about 15 per cent of the final mass gathered through accretion. Supernovae (SNe) and active galactic nuclei (AGN) feedback play an important role in the evolution of these systems. At high redshifts, when the potential wells of the MW progenitors are shallower, winds driven by SNe explosions blow out a large fraction of the gas and metals. As the systems grow in mass, SNe feedback effects decrease and AGN feedback takes over, playing a more important role in the regulation of the star formation activity at lower redshifts. Although model MW galaxies have been selected to lie in a narrow range of maximum circular velocities, they nevertheless exhibit a significant dispersion in the final stellar masses and metallicities. Our analysis suggests that this dispersion results from the different accretion histories of the parent dark matter haloes. Statistically, we also find evidences to support the MW as a typical Sb/Sc galaxy in the same mass range, providing a suitable benchmark to constrain numerical models of galaxy formation.     

Chemical compositions of impact melt breccias and target rocks from the Tenoumer impact crater,Mauritania

Abstract— The impact melt breccias from the Tenoumer crater (consisting of a fine‐grained intergrowth of plagioclase laths, pyroxene crystals, oxides, and glass) display a wide range of porosity and contain a large amount of target rock clasts. Analyses of major elements in impact melt rocks show lower contents of SiO₂, Al₂O₃, and Na₂O, and higher contents of MgO, Fe₂O₃, and CaO, than the felsic rocks (i.e., granites and gneisses) of the basement. In comparison with the bulk analyses of the impact melt, the glass is strongly enriched in Si‐Al, whereas it is depleted both in Mg and Fe; moreover, the impact melt rocks are variably enriched or depleted in some REE with respect to the felsic and mafic bedrock types. Gold is slightly enriched in the impact melt, and Co, Cr, and Ni abundances are possibly due to a contribution from mafic bedrock. Evidences of silicate‐carbonate liquid immiscibility, mainly as spherules and globules of calcite within the silicate glass, have been highlighted. HMX mixing calculation confirm that the impact melt rocks are derived from a mixing of at least six different target lithologies outcropping in the area of the crater. A large contribution is derived from granitoids (50%) and mica schist (17–19%), although amphibolites (?15%), cherty limestones (?10%), and ultrabasites (?6%) components are also present. The very low abundances of PGE in the melt rock seem to come mainly from some ultrabasic target rocks; therefore, the contamination from the meteoritic projectile appears to have been negligible.     

Elemental composition of sediment cores from a mangrove environment using neutron activation analysis

The geochemistry of Sepetiba Bay was studied in four sediment cores using a multi-element approach. Two cores were sampled in the more contaminated eastern part of the bay and two cores were sampled in the western region. The aim was to determine whether less common elements like the rare earths or the actinides are associated with contaminant metals like zinc in the Bay. Samples were analysed by instrumental neutron activation analysis that permits the quantification of total concentrations of metals (Ba, Co, Cr, Cs, Fe, Hf, Rb, Sc, Zn), rare earth elements (Ce, Eu, La, Lu, Sm and Yb), actinides (Th, U), non-metals and semi-metals (As, Br). Organic carbon and total sulphur were also analysed. The results show very strong zinc contamination in the top layers (more than 1000 μg g⁻¹) and background concentrations in the bottom (15 μg g⁻¹). Elements like chromium which would be expected to be released by the heavy industries of Sepetiba Bay, did not show a contamination profile, and concentrations remained close to those of natural environments. No evidence of any association between the zinc and other potential contaminant elements could be identified in this work.     

Morphology and mechanism of eruption of postglacial shield volcanoes in Iceland

Postglacial Icelandic shield volcanoes were formed in monogenetic eruptions mainly in the early Holocene epoch. Shield volcanoes vary in their cone morphology and in the areal extent of the associated lava flows. This paper presents the results of a study of 24 olivine tholeiite and 7 picrite basaltic shield volcanoes. For the olivine tholeiitic shields the median slope is 2.7°, the median height 60 m, the median diameter 3.6 km, the median aspect ratio (height against diameter) 0.019, and the median cone volume 0.2 km³. The picritic shield volcanoes are considerably steeper and smaller. A shield-volcano cone forms from successive lava lake overflows which are of shelly-type pahoehoe. A widespread apron surrounding the cone forms from tube-fed P-type pahoehoe. The slopes of the cones have (a) a planar or slightly convex form, (b) a concave form, or (c) a convex-concave form. A successive stage of a shield volcano is determined on the basis of cone morphology and lava assemblages. A shield-producing eruption has alternating episodes of lava lake overflows and tube-fed delivery to the distal parts of the flow field. In the late stages of eruption, the cone volume increases in response to the increased amount of rootless outpouring on the cone flanks. Normally, only a small percentage of the total erupted volume of a shield volcano, sometimes as little as 1–3%, is in the shield volcano cone itself, the main volume being in the apron of the shield.     

On the possibility of using metal unblanketed model atmospheres for analysis of population II stars

A comparison between model atmosphere grids with and without metal blanketing has been performed in the low-temperature range (T _eff=6000 K to 10000 K) and for different metal contents (logA=0, –1, –2;A=scaled solar abundance). ForA10^–1 andT _eff7000 K, the Johnson colour indicesU-B andB-V, together with the Strömgrenu-b, b-y and the bolometric correction (BC) are little affected by metal blanketing ( mag<0 _. ^m 04). On the other hand, the trend of the physical quantities and them ₁ andc ₁ colour indices reflect the inadequateness of the models even withA=10^–2 andT _eff=9500 K, where hydrogen line blanketing is expected to dominate. This fact discourages once and for all the use of metal unblanketed atmospheres other than for comparison of colour indices or the calculation of bolometric corrections for Population II A-F spectral types.     

Comparison Between the Energy Flow Networks of Two Habitats in the Venice Lagoon

Abstract. The energy flows of two habitats are quantified and compared by using a trophic network model. The habitats are representative of two typical subsystems of the Venice Lagoon: the seagrass meadows, which represent a mature stage in the ecological succession of lagoon environments, and the Tapes philippinarum fishing grounds, which are subjected to mechanical clam harvesting.
The results obtained for the 'seagrass habitat'are consistent with other field studies, confirming the'key-stone'role played by phanerogams in a lagoon environment. The results for the 'Tapes habitat'show that the energy flow from the sediment to the water column is extremely important. Indeed, the high T. philippinarum biomass cannot be supported solely by the primary production of the local phytoplankton. Instead, this biomass could be supported by a supply provided by the sediment resuspension caused by intensive clam fishing. These findings suggest the presence of a positive feedback between fishing effort and T. philippinarum standing crop.     

Body size–abundance distributions of nano- and micro-phytoplankton guilds in coastal marine ecosystems

This study focuses on body size–abundance distributions of nano- and micro-phytoplankton guilds in coastal marine areas of the Southern Adriatic–Ionian region. The aim of the study was to evaluate the occurrence of common patterns of body size–abundance distributions in relation to physical, chemical and biological environmental forcing factors and to taxonomic composition of phytoplankton guilds. This paper is based on data collected during four oceanographic cruises carried out seasonally along the Southern Apulian coast (Adriatic and Ionian Seas, SE Italy) as a part of the INTERREG II Italy–Greece Program. The study was performed at 21 stations located on 7 transects perpendicular to the coastline, with 3 stations per transect at a distance of 3, 9 and 15 NM from the coastline. At each station, profiles of the major physical features of the water were determined and water samples were collected for phytoplankton and nutrient analysis. Overall, 320 nano- and micro-phytoplankton taxa were identified, 76% of which at species level, with phytoplankton cells ranging in size from 0.008 to 4697.54 ng. Body size–abundance distributions showed some common features: they were relatively invariant (average similarity 65%) with respect to taxonomic composition (average similarity 32%), right skewed (90%), leptokurtic (77%) and log normal (76%). Moreover, abiotic, biotic and spatial ecosystem components accounted for up to 75% of body size–abundance distribution variation. The results of this study suggest that body size–abundance distributions are an intrinsic property of marine phytoplankton communities, emphasising functional dependence on ecological constraints related to trophic factors and intra-guild coexistence relationships.