Thermal history of the evaporitic Haselgebirge mélange in the Northern Calcareous Alps (Austria)

In the central and eastern part of the Northern Calcareous Alps, Upper Permian evaporitic rocks form a tectonic mélange whose distribution is restricted largely to the topmost thrust unit (Juvavicum). Mudrock and dolostone samples associated with the evaporites in ten major outcrops (mostly mines) were examined in order to constrain the paleothermal conditions of the mélange. Measurements of illite "crystallinity" reveal a regionally variable pattern of metamorphic grade ranging from diagenesis to the high anchizone and possibly epizone. Most samples contained very little organic matter and vitrinite particles were rare. Samples containing vitrinite show consistent minimum reflectance values of ～1.3–1.7% R_o, whereas maximum reflectance values are more variable (up to 4.9%). The former data constrain the minimum burial temperatures to ～160–180°C. The observed variability in illite "crystallinity" and organic maturity both between and within individual outcrops is consistent with the mélange architecture of this unit and is in good agreement with the regional thermal pattern recognized in Middle to Upper Triassic carbonate formations within the Juvavicum by conodont color alteration studies. Mélange formation and heating of the evaporites is suggested to be linked to the Upper Jurassic closure of the Meliata-Hallstatt Ocean and subsequent thrusting of obducted terranes (Juvavicum) into the depositional realm of the Northern Calcareous Alps.     

Variability of Sea Surface Heights in the Baltic Sea: An Intercomparison of Observations and Model Simulations

Sea level changes in the Baltic Sea are dominated by internal, short-term variations that are mostly caused by the ephemeral nature of atmospheric conditions over the Baltic area. Tides are small and their influence decreases from western parts of the Baltic Sea to the Baltic Proper. Superimposed to the large short-term sea level changes (up to few decimeters from day to day) are seasonal and interannual variations (centimeters to decimeters). This study focuses on the comparison of sea surface heights obtained from observations and from a high resolution oceanographic model of the Baltic Sea. From this comparison, the accuracy of the modeled sea surface variations is evaluated, which is a necessary precondition for the further use of the oceanographic model in geodetic applications. The model reproduces all observed Baltic sea level variations very reliably with an accuracy of 5 to 9 cm (rms) for short-term variations (up to 2 months) and 8 cm (rms) for long-term variations (>2 months). An additional improvement of the model can be attained by including long-period sea level variations of the North Sea. The model performs well also in the case of extreme sea level events, as is shown for a major storm surge that occurred at the southern coast of the Baltic Sea in November 1995.     

The role of speciation in alkaline igneous fluids during fenite metasomatism

Fenites associated with alkaline igneous rocks show a progression from a high temperature assemblage consisting of sodium-rich alkali feldspar + a sodium-ironrich mafic mineral, to an extreme end member assemblage consisting of pure potassium feldspar + iron oxide. The latter assemblage is only found in association with low temperature carbonatites. Segments of this distribution trend can be found in the contact aureole of single intrusive centers.In the east African Kisingiri nephelinite volcano, ijolite intruded a granodioritic basement, producing a fenitized contact aureole. During metasomatism of granodiorite, according to the mass balance model of Rubie (1982), feldspar only participated in an alkali exchange reaction, while quartz was replaced by sodic pyroxene. Outward from the intrusive contact, with decreasing temperature, feldspar became progressively K-enriched, while pyroxene was enriched in the acmite component. It is predicted that alkaliexchange reactions were controlled by NaCl⁰-KCl⁰ aqueous complexes close to the intrusive contact, while further out in the aureole Na⁺-K⁺ ions dominated at the lower temperatures and enhanced the level of potassium metasomatism of feldspar. With decreasing temperature in the aureole, the K/Na ratio of the fluid decreased and consequently the activity of acmite increased.Around carbonatites, where the level of CO₂ in the escaping fluid can be expected to be high, Na₂CO ₃ ⁰ -K₂CO ₃ ⁰ complexes may dominate. Alkali exchange between feldspar and these aqueous species enhances, even further, the stabilization of pure potassium feldspar. Boiling may also play an important role in potassium metasomatism as carbonatites are frequently associated with pyroclastic rocks. Formation of hematite instead of sodic pyroxene may be attributed to low , high and a CO₂-rich fluid.Important variables which determine the products of alkali metasomatism are shown to be temperature, pressure and CO₂ content of the fluid, as well as the K/Na ratio of the fluid.     

Analysis and interpretation of the paleogeographic distribution of marine sedimentary phosphorites

World-wide distribution of marine phosphorite deposits has been plotted on computergenerated paleogeographic maps of specific geologic time intervals in order to determine if and when optimum arrangements of continents and oceans existed for phosphorogenesis. Geographic input data for the program HYPERMAP consists of digitized continental edges and bathymetry and appropriate coordinates for discrete continental structural blocks. Paleopole and block rotation data were used to construct maps for the following time intervals; Recent, 20, 40, 60, 80, 100, 120, 140, 170–190, 250, 280, 325, 350, 375, 400, 450, 500, and 600 Ma. Phosphorite deposits were plotted directly on the appropriate map according to location and age. The major phosphorites have been divided into four types (A, B, C, D)on the basis of the environment of deposition and facies association. A and B types were deposited in water depths of several hundred meters in association with black shales, chert, and dolomite. In terms of reserves of P ₂ O ₅ they show marked distribution peaks in the Lower and Middle Cambrian and the Permian. C and D types were deposited in water depths of tens of meters in association with quartz siltstones, quartz mudstones, and carbonates. Time distribution peaks in the Lower and Middle Cambrian, the Ordovician, Upper Cretaceous-Eocene, and the Miocene are evident for these deposits. The plotted distributions may be related to a recent model of phosphorite deposition (Sheldon, 1980)which suggests that phosphate levels in ocean water have fluctuated with time. Phosphate content built up during times of high-level warm seas was brought into favorable depositional sites by equatorial and tradewind belt upwelling currents. The paleogeographic analysis shows that maximum phosphorite deposition from equatorial upwelling (type C)occurred north and south of narrow constricted equatorial seaways, at times of high-level warm seas. Maximum deposition of phosphorites from tradewind belt upwelling (types A, B, C, D)occurred when polar oceans were wide and there were extensive north-south trending coasts in low latitudes, at times of transition from high-level warm seas to low-level cool seas.     

Morphological development of the retention basin “Hartheim”: A case study

Flow in rivers and on floodplains is complex as it is affected by several interconnected factors such as topography, sediment transport and vegetation characteristics. The resulting processes are explained by the measure “Hartheim” planned for retention purposes at the Upper Rhine river. On the basis of existing formulas and instruments it is demonstrated that a good estimation of the development of the measure is possible. The proposed procedure is a useful tool for estimating morphological developments of restored river sections.     

A novel approach to the analytical modelling of an auger conveyor system for lunar regolith transportation

Acta Geotechnica - Auger-based transportation systems are a promising method to transport lunar regolith for in situ resource utilisation. An analytical model based on terrestrial auger conveyor...     

C1-C4 hydrocarbons in hydrothermal gases

Twenty-two gas samples from Yellowstone National Park have been analyzed for C₁–C₄ hydrocarbons. All five alkanes in the sequence were identified, two alkenes were identified, and no alkynes were observed. The molecular species present in those samples and the quantitative distribution of those species seems more consistent with an organic orgin (e.g. the thermal degradation of kerogen. etc.) for the hydrothermal gases than with the non-biological production of methane (CO₂ + 4H₂ = CH₄ + 2H₂O) followed by pyrolysis. The latter possibility cannot be completely eliminated, however, since the conditions of reaction are not well known.     

铊-锗-硫三元素相平衡的实验研究

本文用抽真空石英管在干体系中对Tl-Ge-S三元系在300℃等温切面相关系和沿Tl_2-GeS_2及Tl_2-GeS变温切面假二元系相平衡进行了实验研究。 Tl-Ge-S三元系在300℃为三个液相区与三个二元相、八个三元相(包括三个固溶体)和十四个两相区、二十四个三相区稳定共存的复杂相关系。本实验首次合成了三个三元相(Tl_2Ge_(1-x)S_2、Tl_5Ge_(13)S_(24)、TlGe_3S_5)和三个固溶体相,即S·S·a(Tl_2~+Ge~(4+)S_3～Tl_2~+Ge_2~(2+)S_3)、S·S·b(Tl~+Ge_(0.5)~(2+)Ge_(0.5)~(4+)S_2～Tl~+Ge_3~(2+)S_4),S·S·c(Tl~+Ge_2~(2+)S_3～Tl_2~+Ge_5S_6)。     

Anomalous isotopic compositions of Sr,Ar and O in the Mesozoic diabase dikes of Liberia,West Africa

The Mesozoic diabase dikes of Liberia are tholeiites whose ⁸⁷Sr/⁸⁶Sr and ⁸⁷Rb/⁸⁶Sr ratios scatter widely on the Rb-Sr isochron diagram. The problem is attributed to differences in the initial ⁸⁷Sr/⁸⁶Sr ratios of these rocks which range from 0.70311 to 0.70792, assuming a uniform age of 186 Ma for the dikes and using (⁸⁷Rb)=1.42 × 10^–11y^–1. The range of values is similar to that observed in the Mesozoic basalt flows and dikes of other Gondwana continents.New whole-rock K-Ar dates confirm previous conclusions that the diabase dikes in the Liberian and Pan-African age provinces of Liberia absorbed extraneous ⁴⁰Ar after intrusion. Only the dikes in the Paynesville Sandstone have K-Ar dates that range from 117 Ma to 201 Ma and may not contain extraneous ⁴⁰Ar. However, dikes from all three age provinces of Liberia have elevated initial ⁸⁷Sr/⁸⁶Sr ratios. These results indicate that contamination with radiogenic ⁸⁷Sr occurred primarily before intrusion of the magma whereas the addition of extraneous ⁴⁰Ar occurred after emplacement and reflects the age and mineral composition of the country rock.The ¹⁸O values of the Liberian diabase range from +5.6/% to +9.10/% and correlate positively with initial ⁸⁷Sr/⁸⁶Sr ratios. The data can be modeled by fractional crystallization and simultaneous assimilation of crustal rocks by the magma. However, samples containing amphibole and biotite replacing pyroxene deviate from the Sr-O isotope trajectories of the model and appear to have been depleted in ¹⁸O and enriched in ⁸⁷Sr by interactions with groundwater at high temperature.Laboratory for Isotope Geology and Geochemistry Contribution No. 76