Power radiated by a VLF loop antenna in the ionospheric plasma

Summary The radiation power a VLF loop antenna with an arbitrary orientation of the loop's plane relative to the direction of the external magnetic field is calculated and its portion, transferred to the electromagnetic part of the excited spectrum, is determined.

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am umaa m uu am c nu umau nmu uma n m¶rt; a¶rt;um¶rt; n u n¶rt;a ma am mu uu, u¶rt;a ma¶rt;um am am cnma ¶rt;a au.

     

Zircon dating of North Bohemian granulites, Czech Republic: further evidence for the Lower Carboniferous high-pressure event in the Bohemian Massif

U-Pb zircon and rutile multigrain ages and ²⁰⁷Pb/²⁰⁶Pb zircon evaporation ages are reported from high-pressure felsic and metapelitic granulites from northern Bohemia, Czech Republic. The granulites, in contrast to those from other occurrences in the Bohemian Massif, do not show evidence of successive HT/MPLP overprints. Multigrain size fractions of nearly spherical, multifaceted, metamorphic zircons from three samples are slightly discordant and yield a U-Pb Concordia intercept age of 348 ± 10 Ma, whereas single zircon evaporation of two samples resulted in ²⁰⁷Pb/²⁰⁶Pb ages of 339 ± 1.5 and 339 ± 1.4 Ma, respectively. A rutile fraction from one sample has a U-Pb Concordia intercept age of 346 ± 14 Ma. All ages are identical, within error, and a mean age of 342 ± 5 Ma was adopted to reflect the peak of HP metamorphism. Because rutile has a lower closing temperature for the U-Pb isotopic system than zircon, the results and the P-T data imply rapid uplift and cooling after peak metamorphism. The above age is identical to ages for high-grade metamorphism reported from the southern Bohemian Massif and the Granulite Massif in Saxony. It can be speculated that all these granulites were part of the same lower crustal unit in early Carboniferous, being separated later due to crustal stacking and subsequent late Variscan orogenic collapse.     

The chemistry of the minerals of the pyrope dunite from borehole T-7 near Staré (Bohemia)

Summary The chemical compositions of the primary minerals (olivine, orthopyroxene, clinopyroxene and pyrope) of dunites from borehole T-7 near Staré in the eské stedohoí Mountains (Bohemia) as well as those of the minerals forming coronas around violet pyrope in these rocks (i. e. pyrope, clinopyroxene, Cr-rich spinel, and—in the rims—orthopyroxene) were determined by electronmicroprobe analysis. The chemical relationships between the bulk composition of dunite and lherzolite and that of their constituent minerals are discussed on the basis of analyses from the literature and the new ones. In comparison to lherzolite, dunite and all its minerals contain more magnesium and chromium, but less iron, aluminum and titanium.ThePT conditions of the formation of the symplectites of the coronas around pyrope are considered not to be very different from those of the minerals of the dunite matrix.

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Der Chemismus der Minerale des Pyrop-Dunites aus der Bohrung T-7 bei Staré (Böhmen)

Zusammenfassung Die chemische Zusammensetzung der Primärminerale (Olivin, Orthopyroxen, Klinopyroxen und Pyrop) der Dunite aus der Bohrung T-7 bei Staré im Böhmischen Mittelgebirge (Böhmen) und diejenige der Minerale der Reaktionssäume um violetten Pyrop in diesen Gesteinen (nämlich Pyrop, Klinopyroxen, Cr-reicher Spinell und-an den Säumen — Orthopyroxen) wurde mit Elektronenmikrosonde-Analysen bestimmt. Aufgrund der Analysen aus der Literatur und der neuen werden die Zusammenhänge zwischen den Gesamtchemismen der Dunite und Lherzolithe mit demjenigen ihrer Minerale diskutiert. Im Vergleich zum Lherzolith enthalten der Dunit und alle seine Minerale relativ mehr Magnesium und Chrom, aber weniger Eisen, Aluminium und Titan.Es wird angenommen, daß diePT-Bildungsbedingungen der Symplektite in den Reaktionssäumen um Pyrop nicht sehr verschieden von denen der Minerale der Dunit-Matrix waren.

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With 6 Figures     

The Chemical Background of Eutrophication in the Skalka-Reservoir

Through a power plant an inflow of considerably heated and very eutrophic water gets into the polymikt reservoir (volume h 15.1 · 10⁶m³, 341 ha, MQ6 m³/s). Phosphorus is the limiting nutrient with a relatively high share from agricultural utilization. The spring maximum of phytoplankton is due to chlorophytes and diatoms, and the summer maximum is caused by cyanophyceae (up to 300 colonies/ml). It could be successfully controlled by copper sulphate. This treatment did not produce any negative effects in the free water (0.05 … 0.1 mg/l Cu²⁺) or in the sediment with a storage of about 1 t Cu per year. The construction of preimpoundment reservoirs, however, must be recommended for a lasting solution.     

Eokambrische Tillite der Železné hory,Ostböhmen

Zusammenfassung Es wird zuerst eine kurze übersicht des Algonkiums Mittelböhmens und der elezné hory (Eisengebirge, Ostböhmen) gegeben. Dem Algonkium des nördlichen Teiles der elezné hory lagert schwach diskordant eine epizonal-metamorphe eokambrische Serie auf. Sie besteht aus serizitischen Siltschiefern, normalen und konglomeratischen Grauwacken, arkosenartigen Sandsteinen, dünn gestreiften Schiefern vom warwitischen Typus, mächtigen Konglomeraten und Vulkaniten (spilitischen Porphyriten und Mandelsteinen, Tuffen und Quarzkeratophyren). Die zwei Streifen von Konglomeraten sind petrographisch ausführlicher beschrieben.Der Charakter der Sedimentgesteine, insbesondere der Konglomerate, weist auf einen raschen Ablagerungsproze\ während der starken und schnellen Denudation nach einer vorangehenden Faltungs- und Emergenzphase und unter einem kühlen Klima hin. Lithologische Eigentümlichkeiten der Konglomerate, undeutliche bis fehlende Schichtung, schlechte Sortierung, wenig abgerundetes, oft eckiges Material, unregelmä\ige Einlagerungen von Arkosegrauwacken mit zerstreuten grö\eren Geröllen, ausgezogene Flasern graphitischer Schiefer, an Frostkeile erinnernde Ausfüllungen vertikaler Klüfte, Zerdrückung einiger Gerölle sowie auffällig frische Feldspäte haben uns seinerzeit (F.Fiala, J.Svoboda 1955) zur Auffassung dieser Konglomerate als Tillite geführt. Glaziale Kritzung und Schleifung an Geschieben und auf dem Liegenden der Konglomerate wurde aber nicht festgestellt.Die behandelte eokambrische Serie haben F.Fiala und J.Svoboda 1955 als Subkambrium bezeichnet und angeführt, da\ das Böhmische Massiv nach der älteren (eisengebirgischen, H.Stille 1946) Phase der assyntischen Faltung durch eine Vereisung betroffen wurde, und da\ die subkambrischen (eokambrischen) Sedimente der elezné hory Tillite, bzw. glazimarine bis glazilakustrine warwitische Sedimente darstellen.

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Summary The Algonkian of central Bohemia and especially of the elezné hory Mts. (East Bohemia) is briefly characterized. In the northern spur of the elezné hory the Algonkian is unconformably overlain by a slightly epimetamorphosed series of Eocambrian sedimentary rocks and volcanites. The series consists of silty sericite schists, ordinary and conglomeratic greywackes, arkosic sandstones, thinly banded slates of varvitic type, conglomerates and volcanites, i. e. spilitic porphyrites and amygdaloids, tuffs and quartz keratophyres. The petrography of the two bands of conglomerates is given.The character of the sediments, especially of conglomerates, furnishes evidence of a rapid sedimentation during a strong and sudden denudation which occurred after the preceding phase of folding and emersion and under a cold climate. Lithological peculiarities of the conglomerates, the indistinct to lacking bedding, badly sorted, slightly rounded and often angular clastic material, irregular intercalations of arkosic greywackes with scarcely scattered boulders, stretched streaks of black graphitic slates, infilling of vertical cracks recalling ice-wedges, crushing of some pebbles as well as striking freshness of feldspars led F.Fiala and J.Svoboda 1955 to designate the conglomerates in question as tillites. Nevertheless, glacial striae and polishing have not be found.F.Fiala and J.Svoboda 1955 have designated the Eocambrian series under consideration as Subcambrian assuming that, after the earlier phase of Assyntian folding, the Bohemian Massif was probably affected by glaciation and that the Subcambrian (Eocambrian) sedimentary rocks of the elezné hory Mts. represent tillites, i. e. glaciomarine to glaciolacustrine varvitic sediments.

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Résumé Une vue d'ensemble de l'Algonkien de la BohÊme centrale et des elezné hory (BohÊme de l'Est) est donnée. Dans la partie nord des elezné hory une série éocambrienne des roches sédimentaires et volcaniques épi-métamorphisées est unconformablement superposée à l'Algonkien. Elle est constituée par des schistes silteux à séricite, des grauwackes ordinaires et conglomératiques, des grès arkosiques, des schistes finement laminés rappelant des types varvitiques, des conglomérats et des volcanites (des porphyrites spilitiques, des porphyrites à amygdales, des tuffs et des kératophyres quartzifères). Les caractéristiques pétrographiques des deux bandes des conglomérats sont présentées.Le caractère des sédiments, surtout des conglomérats, témoigne d'une sédimentation très active pendant la dénudation rapide suivant après une phase de plissement et d'émersion et sous un climat froid. C'est que le caractère lithologique spécial des conglomérats, leur stratification indistincte ou absente, assortiment imparfait, matériel élastique un peu roulé et souvent angulaire, les intercalations irrégulières des grauwackes à galets épars, les lambeaux étirés des schistes graphitiques, les remplissages des fentes rappelant coins de glace, le morcellement des galets et la fraÎcheur frappante des feldspaths ont amené F.Fiala et J.Svoboda (1955) à considérer ces roches comme tillites. Mais on n'a pas réussi à rencontrer des stries et des polissages glaciaires. F.Fiala et J.Svoboda (1955) ont désigné cette série pour subcambrienne en supposant qu'après la phase plus ancienne du plissement assyntien le Massif de la BohÊme a été affecté par glaciation et que les sédiments subcambriens (= éocambriens) des elezné hory correspondent aux tillites ou aux sédiments varvitiques d'origine glaciomarine jusque glacio-lacustrine.

     

Cs137 gamma-ray absorption in eclogites

Summary The coefficient of the gamma-ray absorption _Cs ¹³⁷ investigated in eclogites of the Bohemian Massif varies with fresh samples from0.2477 cm ^–1 to 0.2804 cm ^–1 . Symplectite is the main factor decreasing the value of down to0.242 cm ^–1 . On the contrary, the coefficient increases with the increasing content of clinopyroxene and especially of garnet. The linear dependence of the coefficient on the density may be expressed by the equation =0.0682+0.028.     

Emplacement depths and radiometric ages of Paleozoic plutons of the Neukirchen–Kdyn massif: differential uplift and exhumation of Cadomian basement due to Carboniferous orogenic collapse (Bohemian Massif)

The igneous complex of Neukirchen–Kdyn is located in the southwestern part of the Teplá–Barrandian unit (TBU) in the Bohemian Massif. The TBU forms the most extensive surface exposure of Cadomian basement in central Europe. Cambrian plutons show significant changes in composition, emplacement depth, isotopic cooling ages, and tectonometamorphic overprint from NE to SW. In the NE, the V epadly granodiorite and the Smr ovice diorite intruded at shallow crustal levels (<ca. 7 km depth) as was indicated by geobarometric data. K–Ar age data yield 547±7 and 549±7 for hornblende and 495±6 Ma for biotite of the Smr ovice diorite, suggesting that this pluton has remained at shallow crustal levels (T<ca. 350 °C) since its Cambrian emplacement. A similar history is indicated for the V epadly granodiorite and the Stod granite. In the SW, intermediate to mafic plutons of the Neukirchen–Kdyn massif (V eruby and Neukirchen gabbro, Hoher–Bogen metagabbro), which yield Cambrian ages, either intruded or were metamorphosed at considerably deeper structural levels (>20 km). The Teufelsberg ( ert v kámen) diorite, on the other hand, forms an unusual intrusion dated at 359±2 Ma (concordant U–Pb zircon age). K–Ar dating of biotite of the Teufelsberg diorite yields 342±4 Ma. These ages, together with published cooling ages of hornblende and mica in adjacent plutons, are compatible with widespread medium to high-grade metamorphism and strong deformation fabrics, suggesting a strong Variscan impact under elevated temperatures at deeper structural levels. The plutons of the Neukirchen area are cut by the steeply NE dipping Hoher–Bogen shear zone (HBSZ), which forms the boundary with the adjacent Moldanubian unit. The HBSZ is characterized by top-to-the-NE normal movements, which were particularly active during the Lower Carboniferous. A geodynamic model is presented that explains the lateral gradients in Cambrian pluton composition and emplacement depth by differential uplift and exhumation, the latter being probably related to long-lasting movements along the HBSZ as a consequence of Lower Carboniferous orogenic collapse.     

Humic Acids in the Inflows to the Fláje Reservoir after Deforestation of its Watershed

Today only 35% of the catchment area are covered by forests after deforestation, as compared with the original 70%. In connection with that, the concentration of humic matter has decreased from the original 8 mg/1 to 4 mg/1. The analysis of these changes is facilitated by the linear regressions of a high significance which exist between the COD-Mn and humic acid concentration and the colour. Parallel to deforestation, also the nitrate concentration increased, which, however, can be explained by higher nitrogen concentrations in precipitation.     

Transfer impedance of a probe in a drifting plasma

au un¶rt;a umu ¶rt;a na nu nauuu ¶rt;a uam mmu amm na aa. amau aa auum m mnam u mu ¶rt;a, m unam ¶rt; ¶rt;uamuu u na.     

U-Pb zircon and Sm-Nd model ages of high-grade Moldanubian metasediments,Bohemian Massif,Czechoslovakia

We report single grain U-Pb ion-microprobe as well as conventional bulk size fraction ages for zircons from 3 metasediment samples of the Moldanubian Complex, Bohemian Massif, one of the largest crystalline complexes of the Hercynian foldbelt in Europe. These are complemented by whole-rock Sm-Nd model ages. The metasediments are of upper amphibolite to granulite grade and come from the Bory Massif in Moravia, NW of Brno (sample AA-1) and from the Varied Group (AA-2) and Monotonous Group (AA-3) in the Ceske Budejovice region of SW Bohemia.Ion-microprobe data for detrital zircons yielded ²⁰⁷Pb/ ²⁰⁶Pb ages between ca. 1750 Ma and 2680 Ma and reflect chronologically heterogeneous source terrains. One grain in sample AA-1 of the Bory granulite massif may be as old as 2684±14 Ma, and this constitutes the oldest reported zircon age for the Hercynian belt of central Europe. The single grain data are much less discordant than previously published conventional U-Pb analyses from bulk zircon samples and suggest a significant early Proterozoic crust-formation event between 2 and 2.2 Ga ago. The size fraction data are compatible with the single grain ages and give a fairly precise definition of the Hercynian event between 347 and 367 Ma ago while their upper Concordia intercept ages between 1700 and 2050 Ma represent the mean of the respective grain populations and are probably geohronologically meaningless. The Nd whole-rock model ages between 1.7 and 3.0 Ga confirm mid-Proterozoic to Archaean source terrains for the dated metasediments.