P travel-times from Nevada Test Site explosions and the determination of average global P travel-times

An analysis of P travel-times from the Nevada Test Site is carried out using data from 23 explosions between 1966 and 1976. Results show a scatter of travel times which may partly arise in the lower mantle. P travel-times over the distance range 25–100° are 2.0–2.5 s faster than the Jeffreys-Bullen travel times.     

Experimental investigation of the metamorphism of siliceous dolomites

For the reaction: 1 diopside+3 dolomite ?2 forsterite+4 calcite+2 CO₂ (14) the following P _total?T-brackets have been determined experimentally in the presence of a gasphase consisting of 90 mole%CO₂ and 10 mole%H₂O∶1 kb, 544°±20° C; 3kb, 638°±15° C; 5kb, 708°±10° C; 10kb, 861°±10° C. The determination was carried out with well defined synthetic minerals in the starting mixture. The MgCO₃-contents of the magnesian calcites formed by the reaction in equilibrium with dolomite agree very well with the calcite-dolomite miscibility gap, which can be recalculated from the activities and the activity coefficients of MgCO₃ as given by Gordon and Greenwood (1970). The equilibrium constant K _14b was calculated with respect to the reference pressure P ₀=1 bar using the experimentally determined \(P_{total} TX_{CO_2 }\) brackets, the activities of MgCO₃ and CaCO₃ (Gordon and Greenwood 1970; Skippen 1974) and the fugacities of CO₂ Holloway (1977) considering the correction of Flowers (1979). Results are plotted as function of the absolute reciprocal temperature in Fig. 1. For the temperature range of 530° to 750° C the following linear expression can be given for the natural logarithm of K_14b: (g) $$[ln K_{14b} ]_T^P = - \frac{{18064.43}}{{T\left( {^\circ K} \right)}} + 38.58 + \frac{{0.308(P - 1 bar)}}{{T\left( {^\circ K} \right)}}$$ where P is the total pressure in bars and T the temperature in degrees Kelvin. Combining Equation (g) with the activities of MgCO₃ and CaCO₃ gives the equilibrium fugacity \(f_{CO_2 }\) : (i) $$[ln f_{CO_2 } ]_T^P = - \frac{{11635.44}}{{T\left( {^\circ K} \right)}} + 21.09 + \frac{{0.154(P - 1 bar)}}{{T\left( {^\circ K} \right)}}$$ Equation (i) and the fugacities of CO₂ permit to calculate the equilibrium data in terms of \(P_{CO_2 }\) and T (see Fig. 3) or P _total, T and \(X_{CO_2 }\) (see Fig. 5). Combining the \(P_{total} TX_{CO_2 }\) equilibrium data of the above reaction with those of the previously investigated reaction (Metz 1976): 1 tremolite+11 dolomite ?8 forsterite+13 calcite+9 CO₂+1 H₂O yields the stability conditions of the four-mineral assemblage: diopside+calcian dolomite+forsterite +magnesian calcite and the stability conditions of the five-mineral assemblage: tremolite+calcian dolomite+forsterite +magnesian calcite+diopside both shown in Fig. 6. Since these assemblages are by no means rare in metamorphic siliceous dolomites (Trommsdorff 1972; Suzuki 1977; Puhan 1979) the data of Fig. 6 can be used to determine the pressure of metamorphism and to estimate the composition of the CO₂-H₂O fluid provided the temperature of the metamorphic event was determined using the calcite-dolomite geothermometer.     

U-Pb and Rb-Sr dating of a polymetamorphic nappe terrain: The Caledonian Jotun nappe,southern Norway

The Caledonian Jotun nappe in the Tyin area of southern Norway has been investigated using U-Pb analysis of zircon and sphene and Rb-Sr measurements of minerals and whole rocks, with special reference to the reaction of the isotope systems to various kinds of metamorphic event. The nappe consists of Precambrian basement rocks and their cover, inversely thrust over the Baltic shield and its parautochthonous, presumably lower Paleozoic sediments during the Caledonian orogeny. While the nappe basement retained its pre-Caledonian structures, the nappe cover was penetratively deformed and metamorphosed to lower greenschist facies conditions.U-Pb analyses of zircon and sphene ofnappe basement rocks point to the crystallization of a syenitic to monzonitic magma at 1694± 20m.y., the intrusion of gabbros into the syenites and monzonites at 1252_?25⁺²⁸ m.y., and the metamorphism (upper greenschist-lower amphibolite facies) and deformation (gneissification and mylonitization) of the whole complex at 909± 16m.y. Although this latest event caused strong lead loss in all zircon populations, it had no influence on the Rb-Sr system on a whole rock scale. The Caledonian movements did not disturb the U-Pb system of zircon and sphene but strongly influenced the Rb-Sr system in certain minerals and zircon and/or its inclusions (K-feldspar and brown biotite partially, green biotite completely reset).In contrast to the nappe basement, zircons from thecover rocks show pronounced lead loss during the Caledonian metamorphism/deformation — U-Pb analysis give discordia lower intercept ages of 415± 21 m.y. and 395± 6m.y. Again, however, the Rb-Sr whole-rock system has not been reset in Caledonian time. Minerals from the same rocks which provided the zircons give Rb-Sr isochron ages of 390± 11m.y. and 386 ± 20 m.y.Comparison of U-Pb and Rb-Sr results from the nappe basement demonstrates that only the analysis of U-Pb systematics in zircon and especially sphene resolved the 900-m.y. event. Rb-Sr mineral data alone yield ambiguous results.The results from the nappe cover confirm that U-Pb analyses from penetratively deformed sediments are very useful in dating a metamorphic/tectonic event in lower greenschist facies conditions.From the measured cell dimensions of the zircon populations it is concluded that lead can be completely retained in zircon during recrystallization.     

Untersuchungen über die Trübungsverhältnisse,die Durchsichtigkeit und die Wasserfarbe in schweizerischen Gewässern

Zusammenfassung Im ersten, der Festlegung der theoretischen Grundlagen der Trübung gewidmeten Kapitel wird die Sinkgeschwindigkeit kleiner Teilchen auf Grund der Gesetze der ?Schwebetheorie? vonWesenberg-Lund, W. Ostwald sowie der Stokesschen Formel diskutiert. Ein weiteres Kapitel orientiert anhand bisheriger Kenntnisse über die Erscheinungen der Lichtdurchl?ssigkeit (bzw.-absorption) und des Lichtklimas in verschiedenen Tiefen unserer Seen. Die Trübung der in einer Reihe von Flu?systemen und Seen erhobenen W?sser wurde mittels der absoluten Messung im Pulfrich-Stufenphotometer festgestellt. Sodann wurden die analysierten Proben nach steigenden Trübungswerten geordnet und unterteilt in ?Klarseen?, ?mitteltrübe? und ?trübe? Seen. Schliesslich wurde zusammen mitH. Züllig der Grad der Trübung, der Transparenz und die Seefarbe zueinander in Beziehung gebracht, wobei unterschieden wird zwischen Seen, die a) durch vorwiegend anorganische Stoffe, b) durch vorwiegendOscillatoria-armes Plankton, c) durch vorwiegendOscillatoria rubescens getrübt sind. Die in mehreren Tabellen und Abbildungen wiedergegebenen Werte der Wassertrübung spiegeln die unterschiedlichen Verh?ltnisse wider, die sich im Laufe einer ausgedehnteren Flu?strecke oder in einem See ergeben aus der Mischung des verschieden stark mit Schwebestoffen belasteten Wassers von Haupt- und Nebenfluss, sodann aus der fortschreitenden oder von Strecke zu Strecke wechselnden Sedimentation, und natürlich auch von der lokalen oder regionalen Wetterlage (Niederschl?ge und Schneeschmelze). In ausgedehnten und zum Teil über Monate hinweg durchgeführten Sedimentationsversuchen im Laboratorium wurde schliesslich der Kl?rvorgang von W?ssern verschiedener Herkunft in Funktion der Zeit untersucht. Dabei ergaben sich unterschiedliche Kurven, die ein Bild zu vermitteln verm?gen über den mittleren Durchmesser der die Trübung verursachenden sedimentierbaren, anorganischen Partikeln.     

Bifurcations in Spherical MHD Models

A series of numerical studies on the behaviour of magnetic fields and motions in a spherical body of an electrically conducting incompressible fluid have been carried out. The magnetic field was assumed to be maintained by a given electromotive force inside the body and to continue as a potential field in outer space. In view of the motion an external forcing was taken into account, and boundary conditions were considered which correspond to a stress-free surface. The stability of several steady states has been studied as well as the evolutions starting from unstable states. In this paper a configuration with a poloidal magnetic field and a differential rotation, both symmetric about the same axis, is considered. This configuration is stable only for sufficiently small Hartmann numbers but evolves, if disturbed, in the case of larger Hartmann numbers toward a non-axisymmetric state. In this case the well-known symmetrization effect of differential rotation in magnetic fields is destroyed.     

Mean bulk densities of samples of dry atmospheric aerosol particles: A summary of measured data

Mean bulk densities of various samples of dry atmospheric aerosol particles sampled at different sites and during different seasons and weather situations range between 1.8 and more than 3 gm cm³.