Nd-, Sr-, O-isotopic and chemical evidence for a two-stage contamination history of mantle magma in the Central-Alpine Bergell intrusion

Two different contamination processes have been identified as having been operative in the genesis of a plutonic suite: initial contamination of a mantle source, and subsequent crustal contamination of uprising partial melts from the mantle. These processes are indicated by a detailed analyses of Nd, Sr, and oxygen isotopes together with major-and trace-elements of the 32–30 Ma calc-alkaline Bergell intrusion. This intrusion is located at the suture of the Alpine continental collision zone and contains rock types capable of discriminating between mantle and intracrustal processes. A range from basaltic-andesitic dykes in the surrounding country rocks, cumulitic hornblendites, gabbros, tonalite, granodiorite and lamprophyres, to pegmatites and aplites, is exposed in this single intrusion. The results of REE modelling and isotopic compositions of the basic members suggest that the cumulates were fractionated from a picrobasaltic liquid originating by partial melting of enriched subcontinental mantle (_Nd=+4). Increases in ⁸⁷Sr/⁸⁶Sr (0.7055) and ¹⁸O(+6.7) in these samples relative to the mantle array and compositions of other Periadriatic intrusions are most likely the result of an initial contamination of the mantle source by dehydration or partial melting of altered subducted oceanic crust. Slight differentiation of such a picrobasaltic liquid produced the basaltic-andesitic dykes. Simultaneous fractional crystallization and contamination of the uprising magma by continental crust produced crustal isotopic signatures which increase with acidity to values of (_Nd=-7.6), ⁸⁷Sr/⁸⁶Sr=0.716 and ¹⁸O=+10. The crustal imprint and LREE enrichment in the dominating tonalite increase with decreasing crystallization depth which indicates that the tonalites were emplaced in several distinct batches with different degrees of contamination. Shoshonitic lamprophyres, which intruded into the partly solidified granodiorite, were generated in a deep, strongly contaminated mantle source. The posttectonic 26 Ma Novate leucogranite is not cogenetic with the main Bergell body, but rather formed from a predominantly crustal source. If the described features are indeed due to mantle source contamination processes, which are well known for volcanic arcs, it must be concluded that these may also play a significant role in the genesis of calcalkaline plutonic suites.     

Climatic change and design criteria in water resources management a regional case study

As a result of the anthropogenic greenhouse effect there is fear of alterations of the world climate, which also may result in hydrological changes and consequently in water resources management. In a case study it was investigated if such changes could be identified for a regional catchment area. Summarized it may be said that the regional analysis of hydro-meteorological data in the catchment area of the Sieg showed the expected effects of the anthropogenic climate change on the regional water cycle. Rises in annual mean temperature and precipitation could be observed over a period from 1892 until 1993. However, a significant relation between evident changes and greenhouse effect could not be stated. Changes in discharge do not show consistent behavior. Especially apparent contradictions show that additional examinations are necessary in order to make the complex natural inter-relationships between climate and regional water cycle with the impacts of existing anthropogenetic interferences visible and applicable for practical engineering tasks.     

Chemical Mechanism Development: Laboratory Studies and Model Applications

Within the German Tropospheric Research Programme (TFS) numerous kinetic and mechanistic studies on the tropospheric reaction/degradation of the following reactants were carried out: oxygenated VOC, aromatic VOC, biogenic VOC, short-lived intermediates, such as alkoxy and alkylperoxy radicals.At the conception of the projects these selected groups were classes of VOC or intermediates for which the atmospheric oxidation mechanisms were either poorly characterised or totally unknown. The motivation for these studies was the attainment of significant improvements in our understanding of the atmospheric chemical oxidation processes of these compounds, particularly with respect to their involvement in photooxidant formation in the troposphere. In the present paper the types of experimental investigations performed and the results obtained within the various projects are briefly summarised. The major achievements are highlighted and discussed in terms of their contribution to improving our understanding of the chemical processes controlling photosmog formation in the troposphere.     

Erosion-driven uplift of the modern Central Alps

We present a compilation of data of modern tectono-geomorphic processes in the Central European Alps which suggest that observed rock uplift is a response to climate-driven denudation. This interpretation is predominantly based on the recent quantification of basin-averaged Late Holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling. Furthermore, a GPS data-based synthesis of Adriatic microplate kinematics suggests that the Central Alps are currently not in a state of active convergence. Finally, we illustrate that the Central Alps have acted as a closed system for Holocene redistribution of sediment in which the peri-Alpine lakes have operated as a sink for the erosional products of the inner Central Alps.While various hypotheses have been put forward to explain Central Alpine rock uplift (e.g. lithospheric forcing by convergence, mantle processes, or ice melting) we show with an elastic model of lithospheric deformation, that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading. Thus, erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens. Rather, we suggest that the geomorphic response of the Alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift. Therefore, in a non-convergent orogen such as the Central European Alps, the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion.     

FerryBox - Application of continuous water quality observations along transects in the North Sea

In 2002, the Helmholtz-Zentrum Geesthacht, Germany, started to use FerryBox-automated monitoring systems on Ships of Opportunity to continuously record standard oceanographic, biological and chemical in situ data in the North Sea. The present study summarises the operational experience gathered since the beginning of this deployment and reflects on the potential and limits of FerryBox systems as a monitoring tool. One part relates to the instrumental performance, constancy of shipping services, and the availability and quality of the recorded in situ data. The other considers integration of the FerryBox observations in scientific applications and routine monitoring campaigns. Examples are presented that highlight the added value of the recorded data for the study of both long- and short-term variability in water mass stability, plankton communities and surface water productivity in the North Sea. Through the assessment of technical and scientific performance, it is evident that FerryBoxes have become a valuable tool in marine research that helps to fill gaps in coastal and open ocean operational observation networks.     

Organic carbon content in surface sediments—defining regional provinces

Approaches to quantify the organic carbon accumulation on a global scale generally do not consider the small-scale variability of sedimentary and oceanographic boundary conditions along continental margins. In this study, we present a new approach to regionalize the total organic carbon (TOC) content in surface sediments (<5 cm sediment depth). It is based on a compilation of more than 5500 single measurements from various sources. Global TOC distribution was determined by the application of a combined qualitative and quantitative-geostatistical method. Overall, 33 benthic TOC-based provinces were defined and used to process the global distribution pattern of the TOC content in surface sediments in a 1°×1° grid resolution. Regional dependencies of data points within each single province are expressed by modeled semi-variograms. Measured and estimated TOC values show good correlation, emphasizing the reasonable applicability of the method. The accumulation of organic carbon in marine surface sediments is a key parameter in the control of mineralization processes and the material exchange between the sediment and the ocean water. Our approach will help to improve global budgets of nutrient and carbon cycles.     

Paleocene alkaline volcanism in the Nares Strait region: evidence from volcanic pebbles

Paleogene sediments in fault-bounded basins on Judge Daly Promontory, northeast Ellesmere Island, Canadian High Arctic, are rich in volcanogenic material. Volcanic pebbles within the Cape Back basin near Nares Strait were studied for their petrography, geochemistry, Sr and Nd isotopes, and geochronology to identify and characterize their parent rock. The pebbles are derived from lava flows and ignimbrites of a continental rift-related, strongly differentiated, highly incompatible element enriched, alkaline volcanic suite, the proposed Nares Strait volcanic suite, which is distinct from other alkaline volcanic suites on the northern coasts of Ellesmere Island and Greenland. ⁴⁰Ar/³⁹Ar amphibole and alkali feldspar ages indicate that volcanism was active around 61–58 Ma and was probably contemporaneous with sedimentation resulting in Middle to Late Paleocene age for deposition within the Cape Back basin and the other Paleogene basins on Judge Daly Promontory.     

Isotopic dating of pre-Alpidic rocks from the island of Ios (Cyclades,Greece)

The lower tectonic unit of Ios provides evidence of an at least four stage metamorphic and intrusive history which well might be generalized for large parts of the internal Pelagonian.Metamorphic country rocks of unknown age were intruded about 500 Ma ago, as concluded from a Rb-Sr whole rock (WR) isochron on relic tonalites to granodiorites which largely escaped the polyphase postmagmatic overprints.A Hercynian amphibolite facies metamorphism, during which the igneous rocks were partly recrystallized to orthogneisses, is dated by a lower intercept age of 300–305 Ma of U-Pb determinations on zircons and by three almost concordant Rb-Sr muscovite-WR ages of 295 to 288 Ma.K-Ar analyses on these muscovites and on biotites, and Rb-Sr tie lines WR-biotite and WR with other relic magmatic minerals yielded various apparent ages between 260 and 60 Ma. They are interpreted as mixed ages between a Hercynian cooling age and the two stage Alpidic overprints.White micas formed during the Eocene high P/T and/or Oligocene/Miocene Barrovian-type overprints yielded K-Ar dates ranging from 82 to 26 Ma, as well as a single Rb-Sr date of 13 Ma. These Alpidic dates resemble the more detailed age patterns of other Cycladic islands. But they are not sufficient for an independent dating of the Tertiary evolution on Ios island.     

O-Sr isotopic variations in Miocene granitoids from the Aegean: evidence for an origin by combined assimilation and fractional crystallization

Sr, O, and D/H isotopic compositions have been analyzed in Miocene metaluminous to slightly peraluminous (I-type) granitoids of the central Aegean. Individual plutonic complexes display significant variations in their ¹⁸O and initial⁸⁷Sr/⁸⁶Sr compositions.D and ¹⁸O compositions of minerals and whole-rocks are mostly in the magmatic range. Some samples from Naxos and Mykonos/Delos show low D and ¹⁸O values characteristic of meteoric-water-hydrothermal interaction, but as a whole the changes in ¹⁸O and Sr isotopic compositions as a result of hydrothermal alteration were slight, even in instances where marked alteration is petrographically observable. Consequently, the bulk-rock variations of ¹⁸O from 8.1 to 12.0 and of⁸⁷Sr/⁸⁶Sr from 0.70438 to 0.71450 may be regarded as primary and indicative of the conditions of their evolution. Heterogeneous isotopic compositions observed in the individual plutons of Serifos, Ikaria, Samos and Kos may be caused by the multiple intrusion of chemically and isotopically distinct magma pulses, with high viscosities and relatively rapid consolidation in most cases preventing complete homogenization. The granitoids of Serifos, Ikaria and Kos display weak correlations between the initial⁸⁷Sr/⁸⁶Sr and ¹⁸O and 1/Sr. The granitoid province shows a positive correlation between⁸⁷Sr/⁸⁶Sr and ¹⁸O and a non-linear relationship between⁸⁷Sr/⁸⁶Sr and 1/Sr, whereby 1/Sr increases more rapidly than the isotopic ratio as the degree of fractionation of the rocks increases. It is argued that assimilation of older continental material by mantle-derived arc magmas with combined fractionation (AFC) is the most plausible model to explain the chemical and isotopic characteristics of the granitoids and the geological situation in which rock-types trend from granodiorites in the (south)west, near the inferred Oligocene-Miocene suture, to granites in the center and monzonites in the (north)east of the province.