Geochemistry and Rb–Sr geochronology of a ductile shear zone in the Orlica-Śnieżnik dome (West Sudetes, Poland)

Amphibolite-facies orthogneisses of the Orlica-vnie™nik dome in the West Sudetes (Poland) show a local continuous transition from weakly deformed augen gneisses to finely laminated mylonites. Field evidence indicates that ductile shearing developed pre- or syntectonically to a migmatization event. Bulk-rock compositions of variably deformed samples yield no indications for deformation- and/or fluid-enhanced element mobility and redistribution. ⁸⁷Rb-⁸⁶Sr geochronology (biotite, phengite, whole rock) places time constraints on the deformation process and the post-orogenic cooling history. Phengite- and biotite-whole-rock pairs yield Rb-Sr ages of 340 to 334 Ma and 335 to 294 Ma, respectively, independent of the degree of deformation. The weighted mean of phengite-whole-rock pairs indicates an age of 337.4DŽ.3 Ma. Combining most of the biotite-whole-rock data yields a weighted mean age of 328.6dž.4 Ma. Because of their different closure temperatures for the Rb-Sr system, these differences are interpreted to date cooling after a thermal event. Direct dating of the deformation is not possible, but the cooling history record defines a minimum age for the development of ductile shearing and the last migmatization event. These time constraints provide evidence for the initiation of crustal collapse during or immediately following peak metamorphic conditions. The results of this study further document the importance of Variscan metamorphism in the Orlica-vnie™nik dome.     

Geochemistry of oceanic carbonatites compared with continental carbonatites: mantle recycling of oceanic crustal carbonate

Major and trace element and Sr-Nd-Pb-O-C isotopic compositions are presented for carbonatites from the Cape Verde (Brava, Fogo, Sáo Tiago, Maio and Sáo Vicente) and Canary (Fuerteventura) Islands. Carbonatites show pronounced enrichment in Ba, Th, REE, Sr and Pb in comparison to most silicate volcanic rocks and relative depletion in Ti, Zr, Hf, K and Rb. Calcio (calcitic)-carbonatites have primary (mantle-like) stable isotopic compositions and radiogenic isotopic compositions similar to HIMU-type ocean island basalts. Cape Verde carbonatites, however, have more radiogenic Pb isotope ratios (e.g. ²⁰⁶Pb/²⁰⁴Pb=19.3-20.4) than reported for silicate volcanic rocks from these islands (18.7-19.9; Gerlach et al. 1988; Kokfelt 1998). We interpret calcio-carbonatites to be derived from the melting of recycled carbonated oceanic crust (eclogite) with a recycling age of ~1.6 Ga. Because of the degree of recrystallization, replacement of calcite by secondary dolomite and elevated ‘¹³C and ‘¹⁸O, the major and trace element compositions of the magnesio (dolomitic)-carbonatites are likely to reflect secondary processes. Compared with Cape Verde calcio-carbonatites, the less radiogenic Nd and Pb isotopic ratios and the negative Ɨ/4 of the magnesio-carbonatites (also observed in silicate volcanic rocks from the Canary and Cape Verde Islands) cannot be explained through secondary processes or through the assimilation of Cape Verde crust. These isotopic characteristics require the involvement of a mantle component that has thus far only been found in the Smoky Butte lamproites from Montana, which are believed to be derived from subcontinental lithospheric sources. Continental carbonatites show much greater variation in radiogenic isotopic composition than oceanic carbonatites, requiring a HIMU-like component similar to that observed in the oceanic carbonatites and enriched components. We interpret the enriched components to be Phanerozoic through Proterozoic marine carbonate (e.g. limestone) recycled through shallow, subcontinental-lithospheric-mantle and deep, lower-mantle sources.     

Occurrence of naphthalenesulfonates and their condensates with formaldehyde in a landfill leachate and their transport behavior in groundwater of the Upper Rhine Valley, Germany

. Naphthalenesulfonates and their condensation products with formaldehyde are manufactured in the chemical industry for broad application as tanning agents, dispersing agents, and as superplasticizers for concrete. With the disposal of waste they have found their way into the aquatic environment. Five monomeric naphthalenesulfonates and a group of dimeric sulfonated naphthalene-formaldehyde condensates (SNFC) were identified in the leachate and in groundwater observation wells downstream in the plume of the Karlsruhe-West landfill, situated in the Upper Rhine Valley in southwest Germany. For the main monomer of technical SNFC products, 2-naphthalenesulfonate (2-NS), the concentration in the leachate was 170 µg l^–1, which decreased to 9.5 µg l^–1 at a distance of about 300 m from the boundary of the landfill. In the Merdingen tracer test field, the transport of these compounds was studied under more controlled conditions in two tracer experiments with (1) two model compounds, and (2) a technical SNFC product and uranine as a reference tracer. In these experiments, the monomeric naphthalenesulfonates and the SNFC with n=2 behave as conservative tracers. Thus, the findings of the landfill study were supported by these results. Higher molecular SNFC were strongly retarded, which is attributed to adsorption to soil particles. The results of the second tracer experiment suggest a degradation of 2-NS and 2,6-naphthalenedisulfonate (2,6-NDS) after adaptation of the microorganisms in the groundwater aquifer as a consequence of the first tracer experiment.     

Erratum: Comparison of Seismic Dispersion and Attenuation Models: Stud. Geophys. Geod., 46(2002), 293-320

Studia Geophysica et Geodaetica -     

Long-term investigations on the water budget quantities predicted by the hydro-thermodynamic soil vegetation scheme (HTSVS) – Part II: Evaluation, sensitivity, and uncertainty

Summary ¶Various water budget elements (water supply to the atmosphere, ground water recharge, change in storage) are predicted by HTSVS for a period of 2050 days. The predicted water budget elements are evaluated by routine lysimeter data. The results show that land surface models need parameterizations for soil frost, snow effects and water uptake to catch the broad cycle of soil water budget elements. In principle, HTSVS is able to simulate the general characteristics of the seasonal changes in these water budget elements and their long-term accumulated sums. Compared to lysimeter data, there is a discrepancy in the predicted water supply to the atmosphere for summer and winter which may be attributed to the hardly observed plant physiological parameters like root depth, LAI, shielding factor, etc., the lack of measured downward long-wave radiation, and some simplifications made in the parameterizations of soil frost and snow effects. The fact that high resolution data for the evaluation of model results are missing and evaluation is made on the basis of the data from routine stations of a network is typical for the results of long-term studies on climate. Taking into account the coarse resolution of climate models, the coarse vertical resolution that is used in their LSMs, and the lack of suitable parameters needed, it seems that discrepancies in the order of magnitude found in this study are a general uncertainty in the results of land surface modeling on typical spatial and temporal scales of the climate system.Received October 8, 2001; revised February 15, 2002; accepted September 20, 2002 Published online: April 10, 2003     

Whole-rock and sulfide lead-isotope data from the hydrothermal JADE field in the Okinawa back-arc trough

The mineralization of the active hydrothermal JADE field resembles in many aspects the Kuroko-type mineralization. The JADE field is located in a back-arc graben and is associated with a bimodal volcanism. Lead isotope data from igneous rocks, sediments, and ores further emphasize the similarities with the Kuroko ores and suggest that both sediments and volcanic rocks contributed comparable amounts of lead to the deposit. When compared to the sediments, a much larger volume of volcanic rocks must have contributed lead to the deposit, because of the considerably lower lead concentration of volcanic rocks. In contrast to the crustal type lead of the JADE field and the Kuroko-type sulfide deposits the lead isotope signatures of VMS-type deposits at mid-ocean ridges is distinctly different. In the absence of a sedimentary cover it reflects the composition of the mantle source, whereas in the presence of a sedimentary cover it is either a mixture of mantle and sedimentary lead or it may even be completely dominated by the latter. Received: 5 October 1995 / Accepted: 10 May 1996     

The lower marine to lower freshwater Molasse transition in the northern Alpine foreland basin (Oligocene; central Switzerland–south Germany): age and geodynamic implications

The Wilhelmine Alpe section near Immenstadt (Allgäu, south Germany), which represents one of the best continuously exposed outcrops within the northern Alpine foreland basin, has been analyzed for magnetostratigraphic and palynostratigraphic signals. The section comprises the marine-to-terrestrial transition from Lower Marine (UMM) to Lower Freshwater Molasse (USM) sediments. Based on the correlation of the local magnetic pattern with the geomagnetic polarity timescale (GPTS) and palynostratigraphic data, an age of about 31 Ma is suggested for the UMM–USM transition in the Wilhelmine Alpe section. A comparison with coeval magnetostratigraphic sections from central and eastern Switzerland indicates that the regression of the UMM sea along the southern margin of the Molasse basin occurred strongly heterochronously between 31.5 and 30 Ma. The heterochroneity is attributed to the deposition of fan-delta and alluvial fan sediments which document that the overall marine conditions during the UMM were accompanied by strong clastic input derived from the rising Alps. This clastic contribution had a much stronger influence on the depositional pattern than previously thought.     

Redistribution of HFSE elements during rutile replacement by titanite

Titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon. We investigated an amphibolite sample from the Tromsø eclogite facies terrain in Northern Norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite. Patchy compositional zoning of Al, Ti, and F in titanite relates to the presence of a fluid with variable Ti/Al and/or F during its growth. Laser ablation ICP–MS and electron microprobe data for high field strength elements (HFSE: Nb, Zr, Ta, and Hf) of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal (~8 mm) and a systematic decrease towards uniform HFSE contents in the large core. HFSE contents of smaller rutile grains (~0.5 mm) and rutile inclusions (<100 μm) in the titanite overgrowth are similar or higher than in the rims of large rutile crystals. Element profiles from the rim inward demonstrate that HFSE enrichment in rutile is controlled by diffusion. HFSE ratios in diffusion-altered rutile show systematic variations compared with the uniform core composition of the large rutile. Modelling of Zr and Nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid-dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems. Variations of HFSE contents in the newly formed titanite show no systematic spatial distribution. HFSE ratios in titanite and the rims of rutile are different, indicating different solid/fluid distribution coefficients in these minerals. Element fractionation by diffusion into the relict rutile and during fluid-mediated growth of new titanite could substantially change the HFSE budget of these minerals and could affect their use for geochemical tracing and other applications, such as Zr-based geothermobarometry.     

Use of atmospheric radiation measurement program data from Barrow, Alaska, for evaluation and development of snow-albedo parameterizations

Summary Snow albedo is determined from the ratio of out-going to incoming solar radiation using three years of broadband shortwave radiometer data obtained from the Barrow, Alaska, Atmospheric Radiation Measurement (ARM) site. These data are used for the evaluation of various types of snow-albedo parameterizations applied in numerical weather prediction or climate models. These snow-albedo parameterizations are based on environmental conditions (e.g., air or snow temperature), snow related characteristics (e.g., snow depth, snow age), or combinations of both. The ARM data proved to be well suited for snow-albedo evaluation purposes for a low-precipitation tundra environment. The evaluation confirms that snow-age dependent parameterizations of snow albedo work well during snowmelt, while parameterizations considering meteorological conditions often perform better during snow accumulation. Current difficulties in parameterizing snow albedo occur for long episodes of snow-event free conditions and episodes with a high frequency of snow events or strong snowfall. In a further step, the first two years of the ARM albedo dataset is used to develop a snow-albedo parameterization, and the third year’s data serves for its evaluation. This parameterization considers snow depth, wind speed, and air temperature which are found to be significant parameters for snow-albedo modeling under various conditions. Comparison of all evaluated snow-albedo parameterizations with this new parameterization shows improved snow-albedo prediction. Correspondence: Nicole M?lders, Geophysical Institute and College of Natural Science and Mathematics, University of Alaska Fairbanks, 903 Koyukuk Drive, P.O. Box 757320, Fairbanks, AK 99775-7320, USA