Pleistocene mass-flow deposits of basaltic hyaloclastite on a shallow submarine shelf,South Iceland

A Pleistocene subaqueous, volcanic sequence in South Iceland consists of flows of basaltic hyaloclastite and lava with interbedded sedimentary diamictite units. Emplacement occurred on a distal submarine shelf in drowned valleys along the southern coast of Iceland. The higher sea level was caused by eustatic sea-level change, probably towards the end of a glaciation. This sequence, nearly 700 m thick, rests unconformably on eroded flatlying lavas and sedimentary rocks of likely Tertiary age. A Standard Depositional Unit, describing the flows of hyaloclastite, starts with compact columnar-jointed basalt overlain by cubejointed basalt, and/or pillow lava. This in turn is overlain by thick unstructured hyaloclastite containing aligned basalt lobes, and bedded hyaloclastite at the top. A similar lithofacies succession is valid for proximal to distal locations. The flows were produced by repeated voluminous extrusions of basaltic lava from subaquatic fissures on the Eastern Rift Zone of Iceland. The fissures are assumed to lie in the same general area as the 1783 Laki fissure which produced 12 km³ of basaltic lava. Due to very high extrusion rates, the effective water/melt ratio was low, preventing optimal fragmentation of the melt. The result was a heterogeneous mass of hyaloclastite and fluid melt which moved en masse downslope with the melt at the bottom of the flow and increasingly vesicular hyaloclastite fragments above. The upper and distal parts of the flow moved as low-concentration turbulent suspensions that deposited bedded hyaloclastite.     

Predicting ground-motion variations at the Turkey-flat test site,California

Results of a single group participating in an international experiment are analyzed. The experiment served to verify computational predictions of the ground-motion variations due to near-surface geological effects at a site established for that purpose by the California Department of Conservation. Based on an acceleration record at a rock location, and geotechnical model of medium, records at the other locations of a nearby sedimentary deposit were predicted. A 2-D finite-difference sensitivity analysis suggested that the lateral wave-propagation effects are negligibly small, and locally 1-D computations are sufficient for the present site. Those computations are compared with observations not available to the authors during the blind prediction. Peak accelerations, peak velocities and RMS accelerations were predicted with errors less than 159%, 114% and 62%, respectively. Maxima of the response spectra were fitted within a factor of 2. The predicted and observed Husid's plots (i.e., the normalized cumulative plots of the acceleration squared) have the correlation coefficients 0.98. The detected misfits do not show any simple relation to the instrument location, component, frequency, or time.     

Transfer factors of contamination between the German Bight and its tributary waters derived from measured tritium and Cs-137 activity concentrations

Summary Evaluation of the results of radioactivity monitoring in the southern North Sea between 1977 and 1987 has shown that in the water of the German Bight three areas stand out due to their different ratios between salinity and concentration of dissolved Cs-137 and tritium. While salinity steadily increases with greater distance from the coast, the Cs-137 concentration above 34 PSU (Practical Salinity Unit) increases sharply and shows how far water from the western and central North Sea, contaminated by nuclear reprocessing in Sellafield (Irish Sea), reaches into the German Bight. In the 34 to 32.5 PSU range, the influence can be seen of water contaminated by tritium originating in the rivers Rhein, Maas and Schelde, precipitation and the nuclear reprocessing plant at La Hague (Channel). Below 32.5 PSU, the influence of the influx from the rivers Elbe, Weser and Ems becomes apparent. These rivers are less contaminated with tritium.Assuming that Cs-137 and tritium, like the salinity of sea water, behave conservatively and that the decay-time of these two isotopes is long compared with the time-scale of water exchange in the southern North Sea, the concentration values measured are used to calculate the structure of the water masses in the three areas of the German Bight mentioned above using the mixing principle. Evaporation is taken into account. Results show that beyond 34 PSU, about half the sea water originates in the western central North Sea while the other half comes from the Channel. Below 34 PSU, the first mentioned share amounts only to a few per cent. Results also show that fresh water from the Rhein delta and precipitation, increasing with a decrease in salinity from 34 to 32.5 PSU, accounts for a maximum of 5% each. The fresh water influx into the German Bight via the rivers Elbe, Weser and Ems amounts to app. 11% when the PSU value reaches 29. The calculated portions are the mean values for the observation period. The number of measurements available makes it impossible to distinguish more exactly between the temporal and spatial variability of the amounts of the individual components.The quantity of each calculated portion of sea water also represents the transfer factor of concentration between the nuclide concentration in the source (e. g. the Rhein) and the concentration in the German Bight. In addition, these factors are used to calculate the transfer factors of discharge using the annual drainage rates of the sources. Thus a radioactive discharge rate of 10¹⁵ Bq per year into the Rhein would produce a mean activity concentration of 0.34 Bq/l in the German Bight (at a salinity of 33.5 PSU). To verify the calculated transfer factors, tritium concentrations in the German Bight are derived from existing environmental tritium data and the results are compared with the values actually measured.

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Transferkaktoren zwischen der Deutschen Bucht und ihren Zuflüssen abgeleitet aus der Tritium- und Cs-137-Aktivitätskonzentration in den beteiligten Gewässern

Zusammenfassung Eine zusammenhängende Auswertung der Meßergebnisse der Radioaktivitätsüberwachung in der südlichen Nordsee über den Zeitraum 1977 bis 1987 hat gezeigt, daß im Wasser der Deutschen Bucht deutlich drei durch den Salzgehalt des Meerwassers und die Konzentration der gelösten Radionuklide charakterisierte Bereiche zu unterscheiden sind.Während der Salzgehalt mit wachsender Entfernung von der Küste stetig zunimmt, steigt die Cs-137-Konzentration oberhalb 34 PSU (Practical Salinity Unit) sprunghaft an und signalisiert die Grenze, bis zu der das durch die Kernbrennstoff-Wiederaufarbeitung in Sellafield (Irische See) kontaminierte Meerwasser der westlichen und mittleren Nordsee in die Deutsche Bucht vordringt. Im Bereich 34 bis 32,5 PSU ist das von Westen zugeführte, stärker Tritium-kontaminierte Wasser aus Rhein, Maas, Schelde und atmosphärischem Niederschlag zu erkennen, an das sich unterhalb 32,5 PSU der geringer mit Tritum kontaminierte Zufluß aus Elbe, Weser und Ems anschließt.Davon ausgehend, daß sich Cs-137 und Tritium wie der Salzgehalt im Meerwasser konservativ verhalten und daß weiterhin die Halbwertzeit des radioaktiven Zerfalls dieser beiden Nuklide lang ist gegenüber den Wasseraustauschzeiten im betrachteten Meeresgebiet, wurden die in der südlichen Nordsee gemessenen sowie aus der Literatur für den Süßwasserbereich entnommenen Konzentrationswerte dazu genutzt, um rechnerisch mit Hilfe des Mischungsgesetzes den Wassermassenaufbau in den drei genannten Salinitätsbereichen in der Deutschen Bucht quantitativ zu bestimmen. Es zeigte sich, daß oberhalb von 34 PSU das Meerwasser aus etwa gleichen Teilen aus der westlichen/mittleren Nordsee und dem Kanal stammt, während unterhalb dieser Salzgehaltsgrenze nur noch mit wenigen Prozentanteilen Wasser aus der mittleren Nordsee zu finden ist. Ferner ergab sich, daß das aus dem Rheinmündungsbiet bzw, aus dem atmosphärischen Niederschlag stammende Süßwasser — mit sinkendem Salzgehalt steigend — bei 32,5 PSU einen maximalen Anteil von jeweils 5% an Meerwasser hat. Der direkte Süßwasserzufluß aus Elbe, Weser und Ems beträgt in die Deutsche Bucht bei 29 PSU ca. 11%.Die berechneten Anteile sind Mittelwerte über den gesamten Beobachtungszeitraum; die Anzahl der Messungen läßt eine genauere Unterscheidung in zeitliche und räumliche Variabilität der Zusammensetzung nicht zu.Die Größe des jeweils bestimmten Anteils am Meerwasser stellt gleichzeitig den Transferfaktor der Konzentration zwischen der Nuklidkonzentration im Ursprungsgewässer (z. B. dem Rhein) und der sich daraus einstellenden Konzentration in der Deutschen Bucht dar. Ferner wurden die Transferfaktoren der Konzentration in Verbindung mit aus der Literatur entnommenen Größen der jährlichen Abflußmengen der Ursprungsgewässer genutzt, um auch die Transferfaktoren der jährlichen Einbringung zu ermitteln. So ergibt die jährliche Einbringung von 10¹⁵ Bq eines Nuklides z. B. in den Rhein bei 33,5 PSU in der Deutschen Bucht eine mittlere Konzentration von 0,34 Bq/l.Als Anwendungsbeispiel und zur Überprüfung der Richtigkeit der Transferfaktoren wird die Auswertung des Tritiumauslasses bei La Hague auf die Deutsche Bucht berechnet und mit den gemessenen Werten verglichen.

     

Lead isotope and Pb-Pb model age determinations of ores from Central Europe and their metallogenetic interpretation

The paper presents lead isotope data from 211 samples from Phanerozoic lead-bearing ore occurrences in Central Europe, particularly from the Southern part of the former German Democratic Republic. The data are interpreted in terms of Amov's dynamic model of continuous lead isotope evolution. The relationships between thoro-genic and urano-genic model ages and the source of lead in different regional units are discussed. We observed differences in lead isotope evolution in the Hercynian internides and externides. Within the Moldanubian and Saxothuringian zones we distinguish five main lead-bearing ore associations: (1) Cambrian, stratiform base metal (Hermsdorf-Waldsassen; ²⁰⁶Pb/ ²⁰⁴Pb=17.50–17.70), (2) Devonian, vein type Sb-bearing, metamorphogene (neumühle-Hartmannsdorf; 17.80–18.00), (3) Upper Carboniferous-Permian, polymetallic, including tin, vein type (Kutna hora-Freiberg-Altenberg; 18.00–18.20), (4) Triassic (-Jurassic), Pb–Ba, vein type (Stibro-Halsbrücke; 18.20–18.60), (5) Cenozoic, polymetallic, vein type, riftogene (Roztoky-Banska tiavnica; 18.80–19.10). Pb isotope characteristics from ores of the Montagne Noire and the Brioude-Massiac district correspond to this subdivision. Ore associations from the Rheno-Hercynian zone display higher ²⁰⁷Pb/²⁰⁴Pb ratios which can be explained by more evolved and less metamorphosed source rocks. Mineralizations of the eastern Harz (Straßberg-Neudorf) belong to the Permian association, those from the western Harz (Clausthal-Bad Grund) to the Triassic-Jurassic. Because of Pb isotope agreement the stratabound Rammelsberg and the vein bound Ramsbeck-I mineralization are presumed to be isogenetic. Pb isotope identity of distinct mineralizations in the basement zone (Halsbrücke-Bad Grund) and in the Triassic sediments (Gorny Slask-Mechernich-Bleiglanzbänke) suggests a strong genetic coherence. Pb isotope conformity between the Upper Carboniferous-Permian-Triassic ore associations and Hercynian postkinematic granitoids, and lamprophyric rocks, also favours a close relationship. Pb isotope and other data indicate crustal sources. As the age of the ore associations decreases, crustal influences generally increase, apart from the Roztoky mineralization.     

Littoral '92

Reports

Littoral '92     

Periodic Hartree-Fock study of minerals: Tetracoordinated silica polymorphs

Periodic Hartree-Fock STO-3G calculations have been performed on several tetracoordinated silica polymorphs: low and high quartz, low and idealized high cristobalite and prototype tridymite. The optimized structural parameters are in overall good agreement with experimental data. In the particular case of -quartz, the SiO₄ tetrahedra are found to be irregular. The optimized values of the two different SiO bond lengths are respectively 1.608 Å and 1.613 Å. The potential energy versus tilt angle curves suggest a picture of the high temperature phases in terms of delocalized oxygen atoms which is consistent with a disordered structure. Finally, the bonding in silica polymorphs is discussed from electron density maps and Mulliken population analysis.     

A layered basic intrusion,deformed and metamorphosed in granulite faciès of the Sri Lanka basement

A layered basic intrusion has been found in the Central Granulite Belt of the Sri Lanka continental basement. It intruded parallel to bedding, before all or early during deformation of neighbouring metasediments. Deformation, affecting metasediments and the intrusion alike, includes flattening to c. 1/20 of the original thickness and NNW-stretching to c. 20 times the original length. The intrusion is now 170–300 m thick. Most of the deformation was acquired under granulite facies metamorphism. The intrusion was then folded, still at high T, by a large F₄-synform with an axis parallel to str₁ and a steep axial plane. A steep axial plane cleavage and minor folds are related to this big fold. Stretching continued along its axis. Late during formation of this fold a granite intruded, mainly following S₄ cleavage planes. The intrusion shows a homogeneous gabbroic series at the bottom, followed upwards by a differentiated and layered series. A thin sequence of ultramafic rocks occurs near the middle. This indicates multiple melt-injection. More homogeneous partly biotite-bearing amphibolites form the top of the succession. Magmatic layering is well preserved, but no magmatic minerals or grain fabrics have escaped deformation or metamorphism. Static annealing under granulite facies conditions outlasted all deformation and was accompanied and followed by the beginning of cooling. Hornblende-Plagioclase coronas formed round garnets at this stage. Geochemical work, carried out by STOSCH (1991) on our samples, confirms the cumulate nature of the rocks.

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Zusammenfassung Eine geschichtete Basische Intrusion wurde im Central Granulite Belt der tiefen, kontinentalen Kruste Sri Lankas entdeckt. Sie intrudierte parallel zur Schichtung in benachbarte Sedimente, vor aller oder sehr früh in deren Deformation. Die Deformation, die Sedimente und die Intrusion in gleicher Weise betraf, führte zu Plättung auf das ca. 1/20 der Ausgangsdicke und zu NNW-Streckung auf das ca. 20fache der Ausgangslänge. Heute ist die Intrusion 170–300 m dick. Der Hauptteil der Deformation wurde unter Granulit-Fazies-Bedingungen erworben. Noch bei hoher T wurde die Intrusion durch eine große F₄-Falte gefaltet. Deren Achse liegt parallel der Streckungsrichtung, stri, ihre Achsenebene ist steil. Eine steile, Achsenebenen-parallele S₄-Schieferung und kleinere Falten entstanden mit ihr. Während der Bildung dieser Falte hielt die Streckung parallel ihrer Achse an. Spät während ihrer Bildung intrudierte ein Granit. Er folgt im wesentlichen S₄. Die Intrusion beginnt unten mit einer homogenen, gabbroiden Serie. Nach oben folgt eine differenzierte, geschichtete. Ein dünnes Paket ultramafischer Lagen erscheint nahe der Mitte. Es weist auf multiple Schmelz-Zufuhr hin. Homogenere Amphibolite, teils mit Biotit, bilden den obersten Teil. Magmatischer Lagenbau ist gut erhalten, lokal mit Gradierung. Magmatische Minerale oder Korngefüge haben Deformation und Metamorphose nicht überlebt. Statische Temperung unter Granulit-Fazies-Bedingungen überdauerte alle Deformation. Sie beginnt und dauert an bei bereits sinkender T. Hornblende-Plagioklas-Koronas bilden sich in diesem statischen Endstadium. STOSCH (1991) untersuchte unsere Proben von der Intrusion geochemisch. Er bestätigte die Kumulatnatur der Gesteine.

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Résumé Une intrusion basique litée a été découverte dans la ceinture centrale granulitique du socle continental du Sri Lanka. L'intrusion s'est effectuée parallèlement à la stratification, avant la déformation des métasédiments encaissants ou tout au début de celleci. La déformation, qui affecte à la fois les métasédiments et l'intrusion, comporte un aplatissement jusqu'à ± 1/20 de l'épaisseur d'origine, et un allongement de ± 20 fois en direction NNW. L'intrusion présente actuellement une épaisseur de 170 à 300 m. La plus grande part de la déformation a été acquise dans les conditions du faciès des granulites. L'intrusion a ensuite été plissée, toujours à haute T, en un large synforme F₄ dont l'axe est parallèle à l'allongement stri et dont le plan axial est vertical. Ce grand pli est accompagné d'une schistosité S₄ plan-axiale redressée et de plis secondaires. L'allongement s'est poursuivi parallèlement à son axe. A la fin de la formation de ce pli, un granite s'est intrudé, qui suit en gros S₄. L'intrusion comporte à sa base une série gabbroïque homogène, suivie vers le haut par une série litée et différenciée. Elle contient, vers son milieu, une intercalation mince de roches ultramafiques. Ceci implique des injections répétées de magma. Le sommet est formé d'amphibolites homogènes partiellement biotitiques. Le litage magmatique est bien conservé, mais aucun minéral ou fabrique magmatique n'a échappé à la déformation et au métamorphisme. Un recuit statique dans les conditions granulitiques a suivi la déformation; il a été accompagné et suivi par le début du refroidissement. A ce stade, des couronnes à hornblende-plagioclase se sont formées autour des grenats. Une étude géochimique, effectuée en 1991 par Stosch sur nos échantillons confirme le caractère de cumulat des roches.

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- . , . , , 1/20 20- NNW . 170–300 . . F₄, str₁, . , S₄, . . . S₄. , , . . , , . coxpa . , .. . , . . . . STOSCH (1991) .

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List of abbreviations ss sedimentary bedding - s₁ first cleavage, plane of first flattening - str₁ Direction of first stretching; although L is usually used for lineations of different kind, including stretching, we use this term to point out that extension is proved in each case - F₂ second folds = first folds folding s₁ - s₂ second cleavage or plane of flattening - F₃ third folds - s₃ third cleavage or plane of flattening - F₄ fourth folds, folding s_1,2,3 and F_1,2,3 - s₄ fourth cleavage or plane of flattening - str₄ direction of fourth stretching - F_5,6 fifth and sixth folds - gf(m) granulite facies (metamorphism) - af(m) amphibolite facies (metamorphism) - KNa-f KNa-feldspar - pg plagioclase - f feldspar - opx orthopyroxene - cpx clinopyroxene - px pyroxene - hb hornblende - bi biotite - cc calcite - do dolomite - qz quartz - mt magnetite     

On the systematic errors of the determinations of the absolute orientation of the meridian marks

The classical method of determination of the absolute azimuth (or Bessel's parameter n) can secure sufficiently precision for RA from observations of stars at high geographical latitudes during polar night only.     

Excitation class of nebulae—An evolution criterion?

A principally new, quantitative system of the classification of the spectra of planetary nebulae is proposed. Spectral class of excitation class of the nebulap is determined according to the relative intensities of emission lines (N ₁+N ₂) [OIII]/4686 HeII and (N ₁+N ₂) [OIII]/H (Table I, Figure 1). The excitation classes are obtained for 142 planetary nebulae of all classes—low (p=1–3), middle (p=4–8), and high (p=9–12⁺) (Tables II, III, and IV). An empirical relationship between excitation classp and mean radius of nebulae is discovered (Figure 2). This relationship as well as excitation classp, as an independend parameter, admit an evolutionary interpretation. It is shown that after reaching the highest class of excitationp=12⁺ the nebulae decrease their class of excitation with the further increases of sizes. The diagram of this relationship has two nearly-symmetric branches — rising and descending with the apogee onp=12⁺ (Figure 2).     

The far UV spectrum of the O4I(n)f star ζ Puppis

A detailed list of line identifications of the far UV spectrum of the O4I(n)f star Puppis (HD 66811) in the wavelength range 1168–1984 Å recorded on 16 April, 1981 with the International Ultraviolet Explorer (IUE) is presented. The detailed analysis of the radial velocities measured in the same wavelength range is also presented.