Protracted fluid-induced melting during Barrovian metamorphism in the Central Alps

The timing and dynamics of fluid-induced melting in the typical Barrovian sequence of the Central Alps has been investigated using zircon chronology and trace element composition. Multiple zircon domains in leucosomes and country rocks yield U–Pb ages spanning from ~32 to 22 Ma. The zircon formed during Alpine melting can be distinguished from the inherited and detrital cores on the basis of their age, Th/U (<0.1) and trace element composition. Ti-in-zircon thermometry indicates crystallization temperatures around 620–700°C. Their composition allows discriminating between (1) zircon formation in the presence of early garnet, (2) zircon in equilibrium with abundant L-MREE-rich accessory phases (allanite, titanite and apatite) typical of metatonalites, and (3) zircon formed during melting of metasediments in feldspar-dominated assemblages. The distribution of zircon overgrowths and ages indicate that repeated melting events occurred within a single Barrovian metamorphic cycle at roughly constant temperature; that in the country rocks zircon formation was limited to the initial stages of melting, whereas further melting concentrated in the segregated leucosomes; that melting occurred at different times in samples a few meters apart because of the local rock composition and localized influx of the fluids; and that leucosomes were repeatedly melted when fluids became available. The geochronological data force a revision of the temperature–time path of the migmatite belt in the Central Alps. Protracted melting over 10 My followed the fast exhumation of Alpine eclogites contained within the same region and preceded fast cooling in the order of 100°C/Ma to upper crustal levels.     

Automobile Emissions of Acetonitrile: Assessment of its Contribution to the Global Source

Based on an estimated global fuel consumption of 2.57 × 10¹⁵g(C) y^–1 and the assumption thatthe fossil fuel burned in Austria is globallyrepresentative, an upper limit of 0.021 (+150%, –50%)Tg y^–1 for global CH₃CN emission dueto fossil fuel burning was obtained from the relativeenhancement of the concentrations of toluene, benzene,and acetonitrile (methyl cyanide) during strong,short-term traffic pollution. This is less than 6% ofthe total global budget of CH₃CN, which is dominatedby an emission rate of 0.8 Tg y^–1 from biomassburning.     

Beitrag zur Kenntnis der Blaualgenvegetation der Thermen von Baden und Leukerbad (Schweiz)

Ohne Zusammenfassung     

Clay catalysis of aromatic hydrogen-exchange reactions

The exchange of aromatic hydrogen in the presence of clay catalysts has been studied by measuring the rates of detritiation of some tritiated naphthalene derivatives on homoionic bentonites. The rate of reaction is influenced by the position of tritium on the ring, the presence of a methoxysubstituent on the ring and the acidity of the clay catalyst. It is inferred that the mechanism of exchange involves an adsorbed species similar to the arenium ion intermediate of electrophilic aromatic substitutions in homogeneous systems. In some cases exchange of hydrogen between acidic clay surfaces and naphthalene derivatives could be detected at temperatures as low as 23°C, and in aqueous slurries at 70°C. This observed reactivity suggests that these reactions could occur in sedimentary environments where organic matter, such as petroleum hydrocarbons, is in contact with clay surfaces. The hydrogen isotopic composition of aromatic hydrogen in petroleum may therefore be related to that of the acidic water adsorbed on clay surfaces with which the petroleum has been in contact.     

On the theory of the geomagnetic dynamo based on mean field electrodynamics

A survey is given on the present state of the geomagnetic dynamo theory which is based on the electrodynamics of mean fields in electrically conducting turbulent media. Models of both the ²-type and the ω-type are taken into consideration, i.e. models where the -effect alone, or together with a differential rotation, gives rise to the regeneration of magnetic fields. Results of special investigations are given and discussed. Models of the ²-type apply to the Earth provided that it shows no noticeable differential rotation. It is pointed out that such models can explain not only the generation of a magnetic field with an axisymmetric dipole-like structure, but also the occurrence of non-axisymmetric components and their westward drift. If, however, a noticeable differential rotation exists, models of the ω-type have to be envisaged. Such models also allow an understanding of the existence of a magnetic field with an axisymmetric dipole-like structure, but they do not provide for a straightforward interpretation of the occurrence and behaviour of the non-axisymmetric components.     

Acid catalysis of alkyl hydrogen exchange and configurational isomerisation reactions: acyclic isoprenoid acids

Acid-catalysed alkyl hydrogen exchange and configurational isomerisation has been studied in a series of acyclic isoprenoid acids when they were heated at 160°C in the presence of a montmorillonite. Hydrogen exchange occurred between the adsorbed water of the clay surface and the a position of the isoprenoid acids. In cases where this position was chiral, exchange was accompanied by configurational isomerisation. Configurational isomerisation occurred more slowly in experiments conducted without a clay matrix in the presence of water. These results have been rationalized in terms of a reaction mechanism involving protonation of the carbonyl oxygen causing enolization and consequent hydrogen exchange at the a position of the acids. This mechanism was used to account for the relatively fast rate of isomerisation of C-2 chiral centres in sedimentary acyclic isoprenoid acids during maturation.     

Stratigraphic Analysis of Upper Cretaceous Rocks in the Mahajanga Basin, Northwestern Madagascar: Implications for Ancient and Modern Faunas

Upper Cretaceous strata of the Mahajanga Basin, northwestern Madagascar, yield some of the most significant and exquisitely preserved vertebrate fossils known from Gondwana. The sedimentology of these strata and their stratigraphic relations have been the focus of renewed geological investigations during the course of five expeditions since 1993. We here designate stratotypes and formalize the terrestrial Maevarano Formation, with three new members (Masorobe, Anembalemba, Miadana), and the overlying marine Berivotra Formation. The Maevarano Formation accumulated on a broad, semiarid alluvial plain bounded to the southeast by crystalline highlands and to the northwest by the Mozambique Channel. The Berivotra Formation was deposited in an open marine setting that evolved from a clastic- to a carbonate-dominated shelf, resulting in deposition of the overlying Betsiboka limestone of Danian age. New stratigraphic data clearly indicate that the Maevarano Formation correlates, at least in part, with the Maastrichtian Berivotra Formation, and this in turn indicates that the most fossiliferous portions of the Maevarano Formation are Maastrichtian in age, rather than Campanian as previously reported. This revised age for the Maevarano vertebrate assemblage indicates that it is approximately contemporaneous with the vertebrate fauna recovered from the Deccan basalt volcano-sedimentary sequence of India. The comparable age of these two faunas is significant because the faunas appear to be more similar to one another than either is to those from any other major Gondwanan landmass. The revised age of the Maevarano Formation, when considered in the light of our recent fossil discoveries, further indicates that the ancestral stocks of Madagascar's overwhelmingly endemic modern vertebrate fauna arrived on the island in post-Mesozoic times. The basal stocks of the modern vertebrate fauna are conspicuously absent in the Maevarano Formation. Finally, the revised age of the Maevarano Formation serves to expand our global perspective on the K/T event by clarifying the age of a diverse, and arguably the best preserved, sample of Gondwanan vertebrates from the terminal Cretaceous.     

A ~565 Ma old glaciation in the Ediacaran of peri-Gondwanan West Africa

International Journal of Earth Sciences - In the Cadomian orogen of the NE Bohemian Massif and of SW Iberia, a post-Gaskiers glacial event dated at c. 565&nbsp;Ma has been detected. Such...     

Assessment of spatial transferability of process‐based hydrological model parameters in two neighbouring catchments in the Himalayan Region

Estimating the hydrological regime of ungauged catchments in the Himalayan region is challenging due to a lack of sufficient monitoring stations. In this paper, the spatial transferability of the model parameters of the process‐oriented J2000 hydrological model was investigated in 2 glaciated subcatchments of the Koshi river basin in eastern Nepal. The catchments have a high degree of similarity with respect to their static landscape features. The model was first calibrated (1986–1991) and validated (1992–1997) in the Dudh Koshi subcatchment. The calibrated and validated model parameters were then transferred to the nearby Tamor catchment (2001–2009). Sensitivity and uncertainty analyses were carried out for both subcatchments to discover the sensitivity range of the parameters in the two catchments. The model represented the overall hydrograph well in both subcatchments, including baseflow, rising and falling limbs; however, the peak flows were underestimated. The efficiency results according to both Nash–Sutcliffe (ENS) and the coefficient of determination (r²) were above 0.84 in both catchments (1986–1997 in Dudh Koshi and 2001–2009 in Tamor). The ranking of the parameters in respect to their sensitivity matched well for both catchments while taking ENS and log Nash–Sutcliffe (LNS) efficiencies into account. However, there were some differences in sensitivity to ENS and LNS for moderately and less‐sensitive parameters, although the majority (13 out of 16 for ENS and 16 out of 16 for LNS) had a sensitivity response in a similar range. The generalized uncertainty likelihood estimation results suggest that the parameter uncertainty are most of the time within the range and the ensemble mean matches very good (ENS: 0.84) with observed discharge. The results indicate that transfer of the J2000 parameters to a neighbouring catchment in the Himalayan region with similar physiographic landscape characteristics is viable. This indicates the possibility of applying a calibrated process‐based J2000 model to other ungauged catchments in the Himalayan region, which could provide important insights into the hydrological system dynamics and provide much needed information to support water resources planning and management.     

Incorporation of aerosol particles between 25 and 850 nm into cloud elements: measurements with a new complementary sampling system

The interpretation of the physico-chemical processes in clouds is facilitated by segregating in situ cloud elements from their carrier gas and small particles (interstitial aerosol). Thus, the present study focuses on the quantitative phase segregation of interstitial air from cloud phase by two complementary samplers with microphysical on-line analysis of the separated phases. An improved counterflow virtual impactor (CVI) was developed for the collection and subsequent evaporation of the condensed phase, releasing dissolved gaseous material and residual particles. This sampler operates in the size range of few micrometers up to 50 μm in cloud element diameter and is matched by an interstitial Round Jet Impactor sampling the gas phase with interstitial particles. Calibrations of both samplers verified the calculated cut sizes D₅₀ of 4, 5, and 6 μm and quantified the slope of the collection efficiency curves. Until this study no direct CVI measurements of the residual particle sizes far below the diameter of 0.1 μm were available. For the first time a CVI was connected to a Differential Mobility Particle Sizer (DMPS) scanning between 25 nm and 850 nm, thus, including the entire Aitken mode in the residual size analysis. Cloud studies on the Puy de Dôme, France, revealed residual particle sizes including Aitken mode (diameter D<100 nm) and accumulation mode (D>100 nm). A major feature of the CVI data is expressed by the fact that despite incomplete incorporation of accumulation mode particles in cloud elements there are contributions of particles with diameters smaller than 0.1 μm to the number of residual particles. Cloud entrainment from height levels above the maximum supersaturation as wells as the size-dependent chemical composition of the aerosol population most likely produced the S-shaped size-dependent partitioning of residual particles. Compared to earlier studies the 50% partitioning diameters dropped significantly below 100 nm to roughly 70 nm.