A New Genus and Species of Damsel-Dragonfly (Odonata: Isophlebioidea: Campterophlebiidae) in the Middle Jurassic of Inner Mongolia, China

The campterophlebiid new genus and species Ctenogampsophlebia reni is described from the Middle Jurassic of Inner Mongolia, China. It shows close similarities with the Lower to Middle Jurassic genera Gampsophlebia, and Petrophlebia, with closed and short subdiscoidal cells, confirming the attribution of these two other genera to the Campterophlebiidae.     

Comparison of quantitative petrographic, stable isotope and cathodoluminescence data for fingerprinting Czech marbles

Various marbles from both historic quarries and historical artefacts of the Czech Republic were examined in order to make determinations of their provenance. The methodology used was based upon a combination of petrographic image analysis (PIA) of thin sections, stable isotope geochemistry of carbonates, and cathodoluminescence. Multivariate statistical methods (i.e. cluster analysis and discriminant analysis) confirmed the geoscientific relevance of the marble’s different characteristics with a high degree of consistency as well as the enhanced significance of stable C and O isotopes in correlation with the petrographic data. The qualitative cathodoluminescence data provided a useful additional tool to help recognise the fingerprinting of marbles with similar petrographic and/or geochemical characteristics.     

Evolution microtectonique et paléo-champs de contraintes du Bassin de Vienne

Résumé

Une étude des structures cassantes permet de préciser l’évolution tectonique du Bassin de Vienne, généralement considéré comme un bassin de type « pull apart » typique. Le champ de contrainte ottnangien-carpathien (18,5-16, 5 Ma) est caractérisé par une compression NNW-SSE. Pendant le Badénien-Sannanticn (16,5-11 Ma) une zone cisaillante sénestre de direction NE-SW a été formée dans un régime en compression N-S et extension E-W. En liaison avec cette zone décrochante trois types d’extension locale conduisent à une forte subsidence dans les dépression : extension NE-SW parallèle aux accidents sénestres, extension E-W entre les décrochements et extension NW-SE au-dessus des zones décrochantes profondes. Le champ de contrainte vers la fin du Sannaticn est marqué par une compression ENE-WSW, tandis que celui du Pannonicn- récent est similaire á celui du Miocène moyen.

Une rotation de la paléocontrainte maximale horizontale, de NNW-SSE a ENE-SSW est mise en évidence pendant la période Ottnangien-Sannantien (18,5-11 Ma). Cette rotation est parallèle A celle des directions de mise en place des nappes carpathicnnes externes. L’origine des rotation est l’échappement continental des Alpes orientales et des Carpathes septentrionales vers le NE et son blocage graduel d’Ouest en Est au front des nappes carpathiennes. Après ce blocage, l’échappement a continué avec une faible intensité du Pannonien à l’Actuel. Alors que l’échappement a été initié par une compression N-S due á la collision Europe-promontoire Adriatique, le champ de contrainte à l’intérieur des blocs échappés reflète l’effet de leur blocage au front des nappes carpalhiques.     

Changes in Components of the Water Balance in the Croatian Lowlands

Summary ?This paper deals with variations and trends in some components of the water balance: the soil water content; evaporation loss from the soil (from the surface and underlying layers); transpiration; ground water recharge and runoff. These components are calculated by means of the Palmer procedure. This analysis is based on data from Osijek, Croatia from this century (1900–1995). Besides the meteorological input parameters necessary for the water balance calculations, i.e. precipitation, temperature and relative humidity, the pedological characteristics of this area have also been taken into account. Fluctuations have been considered by means of the 11-year binomial filtered series and linear trends were tested by means of the Mann-Kendall rank test. For a closer look on the trends of water balance components, a progressive analysis of the time series was performed, too. The results show a significant increase in potential evapotranspiration and evapotranspiration and decrease in runoff and soil water content has occurred during the century. Received February 22, 1999/Revised August 3, 1999     

Recent Climate Warming: Surface Air Temperature Series and Geothermal Evidence

Long-term (1961 – 1996) meteorological air temperature series together with the reconstructed ground surface temperature histories, obtained by inverting borehole temperature-depth profiles, were used to project regional patterns of the recent (climate) warming rate on the territory of the Czech Republic. The characteristic magnitude of the warming rate of 0.02 –0.03 K/yr was confirmed by the results of several years of monitoring the temperature in two experimental boreholes. The monitoring of shallow temperatures at depths of about 30 –40 m, i.e. below the reach of the seasonal surface temperature variations, can serve as an alternative tool of direct quantitative assessment of the present warming rate. The data also seem to sustain a potential man-made component contributing to the more pronounced recent warming rate observed in the areas of large agglomeration.     

Numerical solution of the linearized fixed gravimetric boundary-value problem

The fixed gravimetric boundary-value problem (FGBVP) represents an exterior oblique derivative problem for the Laplace equation. Terrestrial gravimetric measurements located by precise satellite positioning yield oblique derivative boundary conditions in the form of surface gravity disturbances. In this paper, we discuss the boundary element method (BEM) applied to the linearized FGBVP. In spite of previous BEM approaches in geodesy, we use the so-called direct BEM formulation, where a weak formulation is derived through the method of weighted residuals. The collocation technique with linear basis functions is applied for deriving the linear system of equations from the arising boundary integral equations. The nonstationary iterative biconjugate gradient stabilized method is used to solve the large-scale linear system of equations. The standard MPI (message passing interface) subroutines are implemented in order to perform parallel computations. The proposed approach gives a numerical solution at collocation points directly on the Earth’s surface (on a fixed boundary). Numerical experiments deal with (i) global gravity field modelling using synthetic data (surface gravity disturbances generated from a global geopotential model (GGM)) (ii) local gravity field modelling in Slovakia using observed gravity data. In order to extend computations, the memory requirements are reduced using elimination of the far-zone effects by incorporating GGM or a coarse global numerical solution obtained by BEM. Statistical characteristics of residuals between numerical solutions and GGM confirm the reliability of the approach and indicate accuracy of numerical solutions for the global models. A local refinement in Slovakia results in a local (national) quasigeoid model, which when compared with GPS-levelling data, does not make a large improvement on existing remove-restore-based models.     

Tunneling of seismic body waves through thin high-velocity layers in complex structures

Summary The hybrid ray-reflectivity method is applied to the problem of the transmission of the reflected wave field through a thin high-velocity layer (or through a thin stack of high velocity layers), situated in the overburden of the reflector. In the hybrid ray-reflectivity method, the standard ray method is applied in the smooth parts of the model, and the reflectivity method is used locally at the thin high-velocity layer. With the exception of small epicentral distances, the standard ray method itself fails in such computations. The reason is that a considerable part of the energy for overcritical angles of incidence may be tunneled through the thin high-velocity layer along complex ray-paths, corresponding to inhomogeneous waves. The reflectivity method, applied locally at the thin high-velocity layer, automatically includes all inhomogeneous wave contributions. Thus, the hybrid ray-reflectivity method removes fully the limitations of the standard ray method, but still retains its main advantages, such as its applicability to 2-D and 3-D complex layered structures, flexibility, and low-cost computations. In the numerical examples, the hybrid ray-reflectivity synthetic seismograms are compared with standard ray synthetic seismograms and with full reflectivity computations. The numerical examples show that the hybrid ray-reflectivity method describes the tunneling of seismic energy through a thin high-velocity layer with sufficient accuracy.     

Variational approach to modeling present-time mantle convection

Summary An analogy of the Hellinger-Reissner functional for the Stokes problem is constructed and the way of determining its minimum by means of spherical harmonic vectors and tensors is described. The variational method is applied to a Newtonian mantle in which the body forces were estimated on the basis of global inversion of gravitational and topographic data. The method is then generalized to the case of a realistic rheology (power-law creep), and prospects of the generalised method are briefly discussed.     

Modelling and analysis of electromagnetic fields in 3D inhomogeneous media

The main progress in the 3D modelling of electromagnetic fields, achieved during the last few years, is summarized. Various 3D numerical modelling techniques are described and compared as to their possibilities and efficiency. Numerical studies are complemented by laboratory scale modelling.Conventional methods of the analysis of the magnetotelluric and magnetovariational surface characteristics are confronted with new trends in MT tensor analysis and decomposition. Various approaches to the analysis of simplified 3D structures are also presented.     

Primary compositional range and alteration trends of microlite from the yellowknife pegmatite field,Northwest territories,Canada

Summary Microlite occurs as a rare accessory mineral in beryl-columbite, beryl-columbitephosphate, complex spodumene, albite-spodumene and amblygonite type rare-element granitic pegmatites in the Archean Yellowknife pegmatite field of the Canadian Shield. The chemistry of microlite is variable but consistent with the accepted structural formula A_2–mB₂X₆Y_1–n pH₂O, where generally A = Ca,Na; B = Ta,Nb; X = O; Y = O,OH, F; m = 0 - 2; n = 0 - 1 and p = 0 - l. The chemistry of the Yellowknife microlite is dominated by Ca, Na, Ta, and Nb with minor amounts of U, Pb, Fe, Mn, and Ti. The compositions of microlite are interpreted to reflect primary variability and effects of late-stage alteration.Two principal types of microlite can be distinguished by their primary composition and alteration trends. U-poor microlite originated by the metasomatic replacement of pre-existing manganocolumbite, manganotantalite, and ferrotapiolite; with progressive alteration, its composition evolves from early Ca-rich, Fe,Mn-poor members to late Ca,Na-poor, Fe,Mn-enriched members. In contrast, U-bearing microlite formed from U-enriched, moderately fractionated pegmatitec fluids acting upon ferrocolumbite, manganocolumbite, and manganotantalite; with progressive alteration, its composition evolves from U,Ca,Na-enriched members to U,Ca,Na-poor, Fe,Mn-enriched members.

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Primärer zusammensetzungsbereich und umwandlungstrends der mikrolithe aus dem yellowknife pegmatitfeld, Northwest Territories, Kanada

Zusammenfassung Primärer Zusammensetzungsbereich und Umwandlungstrends der Mikrolithe aus dem Yellowknife Pegmatitfeld, Northwest Territories, Kanada Mikrolith kommt in den Beryll-Columbit-, Beryll-Columbit-Phosphat-, komplexen Spodumeri-, Albit-Spodumen- und Amblygonit-Typen der Seltene-Element-Granitpegmatite im archäischen Yellowknife Pegmatitfeld des Kanadischen Schildes als seltenes akzessorisches Mineral vor. Der Chemismus des Mikroliths variiert, ist aber mit der gebräuchlichen Strukturformel A_2–mB₂X_1–mY_1–n·pH₂O verträglich, mit im allgemeinen A = Ca,Na, B = Ta,Nb, X = O, m=0–2, n =O–1 und p=0–1. Der Chemismus des Yellowknife Mikroliths wird durch Ca, Na, Ta und Nb dominiert, U, Pb, Fe, Mn und Ti treten in kleineren Mengen auf. Die Zusammensetzungen des Mikroliths spiegeln die primäre Variabilität sowie die Auswirkungen späterer Umwand lungen wieder.Zwei Haupttypen des Mikroliths können nach ihrer primären Zusammensetzung und den Umwandlungstrends unterschieden werden. U-armer Mikrolith entstand durch metasomatischen Ersatz von früherem Manganocolumbit-Manganotantalit und Ferrotapiolith, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von frühen Ca-reichen, Fe,Mn-armen Gliedern zu späten Ca,Na-armen, Fe,Mn-angereicherten Gliedern. Im Gegensatz dazu bildete sich U-haltiger Mikrolith aus an U angerereicherten, mäßig fraktionierten pegmatitischen Fluiden, die auf Manganocolumbit-Manganotantalit einwirkten, mit fortschreitender Umwandlung entwickelt sich seine Zusammensetzung von U,Ca,Na-angereicherten Gliedern zu U,Ca,Na-armen, Mn,Feangereicherten Gliedern.

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With 9 Figures