Granitoids in the Rozvadov Pluton,Western Bohemia and Oberpfalz

The Rozvadov Pluton is a complex of mainly Variscan granitoid rocks situated near the Bohemian-Bavarian border between Bärnau, Tachov, Rozvadov and Waidhaus, 25 km ESE of the KTB site. Five mappable units can be distinguished, which intruded as folows: (1) slightly deformed leucocratic meta-aplite/metapegmatite dykes with garnet and tourmaline; (2) a complex of cordierite-bearing granitoids, which have been divided into three facies (a) biotite granite with cordierite (at the margin of the complex), (b) biotite-cordierite granite and (c) cordierite tonalite (in the centre of the complex; (3) fine-grained biotite granite of the Rozvadov type with associated pegmatite bodies; (4) two-mica Bärnau granite; and (5) geochemically specialized albite-zinnwaldite-topaz granite (Kríový kámen/Kreuzstein granite) with indications of Sn-Nb-Ta mineralization and associated phosphorus-rich pegmatite cupolas. Rare earth element data suggest that meta-aplite/pegmatite dykes are the result of a batch partial melting process, whereas the compositional variation of the other rock types was mainly controlled by fractional crystallization. The genesis of the cordierite granitoid suite is best explained in terms of a batch melting of metapelitic source followed by crystallization of a cordierite-rich cumulate and K-feldspar enriched melt. The leucocratic pluton constituents — the meta-aplites and the Bärnau and Kíový kámen granites are rich in phosphorus (0.5–0.8%). The main carriers of phosphorus are alkali feldspars, especially K-feldspar (up to 0.8% P₂O₅). The presence of P-rich leucocratic granites is one of the features distinguishing the Variscan granitoids within the Moldanubian zone from the nearly contemporaneous granitoids in the Saxothuringian zone.     

Quartz and feldspar zoning in the eastern Erzgebirge volcano-plutonic complex (Germany, Czech Republic): evidence of multiple magma mixing

Zoned quartz and feldspar phenocrysts of the Upper Carboniferous eastern Erzgebirge volcano-plutonic complex were studied by cathodoluminescence and minor and trace element profiling. The results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends, magma mixing and recharge events, and suggest that much heterogeneity in plutonic systems may be overlooked on a whole-rock scale. Multiple resorption surfaces and zones, element concentration steps in zoned quartz (Ti) and feldspar phenocrysts (anorthite content, Ba, Sr), and plagioclase-mantled K-feldspars etc. indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern Erzgebirge volcano-plutonic complex. Generally, feldspar appears to be sensitive to the physicochemical changes of the melt, whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas. The regional distribution of mixing-compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late-Variscan granites and associated volcanic rocks.

Quartz phenocrysts from 14 magmatic phases of the eastern Erzgebirge volcano-plutonic complex provide information on the relative timing of different mixing processes, storage and recharge, allowing a model for the distribution of magma reservoirs in space and time. At least two levels of magma storage are envisioned: deep reservoirs between 24 and 17 km (the crystallisation level of quartz phenocrysts) and subvolcanic reservoirs between 13 and 6 km. Deflation of the shallow reservoirs during the extrusion of the Teplice rhyolites triggered the formation of the Altenberg-Teplice caldera above the eastern Erzgebirge volcano-plutonic complex. The deep magma reservoir of the Teplice rhyolite also has a genetic relationship to the younger mineralised A-type granites, as indicated by quartz phenocryst populations. The pre-caldera biotite granites and the rhyodacitic Schönfeld volcanic rocks represent temporally and spatially separate magma sources. However, the deep magma reservoir of both is assumed to have been at a depth of 24–17 km. The drastic chemical contrast between the pre-caldera Schönfeld (Westfalian B–C) and the syn-caldera Teplice (Westfalian C–D) volcanic rocks is related to the change from late-orogenic geotectonic environment to post-orogenic faulting, and is considered an important chronostratigraphic marker.     

An analytical model of seismic travel times for a spherically asymmetric Earth

Summary A general analytical model for travel times of seismic waves propagating in a radially asymmetric Earth, is suggested. It is represented by a series of irreducible spherical tensor products with bipolar spherical coefficients. The main term of the series describes the travel times in a radially symmetric Earth, the others represent corrections due to the spherical assymmetry. The method of least squares is suggested for determining the bipolar spherical coefficients from observed seismic travel times. Since the proposed theory assumes that the analytical representation is related to the reference earth, the corrections to the non-zero focal depth and non-zero sea-level height of the seismographic station must be introduced.

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Statistical Postprocessing of NWP Model Outputs Applied to Maximum and Minimum Temperature Forecasts

Statistical postprocessing of NWP model outputs is applied to maximum and minimum temperature forecasts. Two approaches to its application are effected to local short-range weather forecasts of minimum and maximum temperatures: Model Output Statistics and modified Perfect Prognosis. The modified Perfect Prognosis method is restricted to the first step of PP because of the significant difference between the horizontal resolution of the available objective analyses and the NWP model outputs. The modified Perfect Prognosis method uses actual data from the objective analysis related to the forecast period instead of the NWP forecast. The results are compared with a simple statistical prognostic model, which does not utilize the NWP model outputs, and with simple reference methods. The forecast is verified using ground station measurements from stations providing SYNOP reports. The results show that the predictive accuracy of the Model Output Statistics method is not very different from that of the modified Perfect Prognosis method, and both are significantly more accurate than the direct predictions of the NWP model. The results have confirmed that statistical postprocessing is able to make localized predictions even if lowresolution data are used.     

Seismic noise at the international gravity point in Prague-Ruzyně (Czechoslovakia)

Summary The vertical component of ground displacement was measured at the Prague - Ruzyn International Gravity Point in the frequency range of 1–300 Hz. The permanent noise, the vibrations caused by the observers during gravimetric observations and by the wind, as well as those due to normal operations at the airport, display maximum peak-to-peak amplitudes of 0.06 µm in the frequency range of 1–50 Hz; with a CG-2 gravimeter this is not detrimental to the accuracy of the observations. The taxiing of turbo-jet and jet aircraft and engine tests of aircraft generate vibrations in frequency ranges of 75–90 and 190–270 Hz. Their amplitudes, according to the results of laboratory tests published for various types of gravity meters (CG-2, GAK-PT, GVP-3, KVG), are of magnitudes which generate errors in tenths of mgl.     

Differences between Mean Sea Levels for the Pacific,Atlantic and Indian Oceans From Topex/Poseidon Altimetry

Geopotential values W of the mean equipotential surfaces representing the mean ocean topography were computed on the basis of four years (1993 - 1996) TOPEX/POSEIDON altimeter data: W = 62 636 854.10m ² s ^–2 for the Pacific (P), W = 62 636 858.20m ² s ^–2 for the Atlantic (A), W = 62 636 856.28m ²s^–2 for the Indian (I) Oceans. The corresponding mean separations between the ocean levels were obtained as follows: A – P = – 42 cm, I– P = – 22 cm, I – A = 20 cm, the rms errors came out at about 0.3 cm. No sea surface topography model was used in the solution.     

Hercynian-thrust related shear zones and deformation of the Varied Group on the contact of granulites/Southern Moldanubian,Bohemian Massif/

The three deformation phases inferred from the detailed structural analysis of the Cesky Krumlov Varied Group record the Hercynian development of the Southern Moldanubian of the Bohemian Massif. The deformation is related to the NW-SE thrusting of the large crustal units including granulites. The formation of the NS and NW-SE trending shear zones is connected with the thrust movement. The structural development begins with F₁ isoclinal fold formation, that could originate in unmetamorphosed sediments. In the final stage, they were strongly flattened and B₁ boudinage developed in the rocks. Aplite dykes and migmatitization of paragneisses occurred at the same time the rocks were metamorphosed. The D₂ deformational phase was produced by the simple shear deformation of the unit and folds of various styles around rigid inclusions and the strike-slip shear zone near the boundary of the granulite and the Varied Group were formed. The F₁ and F₂ folds are parallel with the stretching and mineral lineation indicating a NS to NW-SE direction of the thrusting. The youngest deformation is characterized by spectacular boudinage and by folding of the vertically oriented planes.

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Zusammenfassung Drei Deformationsphasen der variszischen tektonischen Entwicklung sind in der Bunten Gruppe des südlichen Moldanubikums des Böhmischen Massivs enthalten. Die Deformation ist mit der von NW nach SE orientierten überschiebung von gro\en Krusteneinheiten mit Granuliten verbunden. Die Entstehung von jüngeren N-S und NW-SE verlaufenden Scherzonen kann auf die überschiebungsbewegung bezogen werden. Die Strukturentwicklung beginnt mit F₁ isoklinalen Falten, die wahrscheinlich den nichtmetamorphisierten Sedimenten aufgeprägt wurden. Während der Abschlu\phase der Formung wurden sie stark geplättet und es entstand die B₁ Boudinage. Die Aplitgänge, Migmatitisation der Paragneisse und Metamorphose der Gesteine sind gleichzeitig. Die D₂ Deformationsphase wurde durch einfache Scherung der Einheit hervorgerufen und es entstanden Falten verschiedenen tektonischen Stils in der Umgebung starrer Einschlüsse und die Blattverschiebung an der Grenze von Granulit und Bunter Gruppe. Die F₁ und F₂ Falten liegen parallel zur Streckungslmeation und überschiebungsrichtung ab. Die jüngste Deformation ist charakterisiert durch eine spektakuläre Boudinage und Faltung der senkrecht stehenden Flächen.

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Résumé L'étude structurale détaillée de la Série Variée du Moldanubien méridional dans le Massif de Bohème a permis de distinguer trois phases de déformation dans le développement tectonique varisque. Cette déformation est liée au charriage, du Nord-Ouest vers le Sud-Est, de grandes unités crustales comportant des granulites. La genèse de zones de cisaillement plus jeunes, d'orientation N-S et NW-SE peut Être liée au mÊme processus de charriage. Le développement structural commence avec des plis isoclinaux F₁ engendrés vraisemblablement dans les sédiments non métamorphisés. Au stade final de leur formation, ils ont été très aplatis et un boudinage B₁ est apparu. L'intrusion de filons d'aplite et la migmatitisation des paragneisses sont contemporaines du métamorphisme. La deuxième déformation D₂ a été le fait d'un cisaillement simple; à ce moment se sont formés des plis de style tectonique très variés, localisés fréquemment autour d'inclusions rigides. De cette étape date également le décrochement ductile entre les granulites et la Série Variée. Les plis F₁ et F₂ sont parallèles à la linéation d'étirement (linéation minérale) qui indique la direction N-S à NW-SE du charriage. La déformation la plus jeune comporte un boudinage spectaculaire et le plissement des plans d'attitude verticale.

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