Pyroxene chemistry and evolution of alkali basaltic rocks from Burgenland and Styria,Austria

Summary The mineral chemistry of several Pliocene alkali basaltic rocks from Burgenland and Styria (Eastern Austria) have been investigated in order to determine the evolution path of the basalt magmas prior to eruption. With their wide range of substitutions, clinopyroxenes provide the best records of the evolution history of rocks. Pyroxene phenocrysts of the investigated basalts show both concentric and sector zoning. The investigation of sector zoned crystals shows, that not only Ti, Al and Fe contents are different in different sectors but there can be significant differences also in their Cr content. This fact apparently suggests that the distribution of Cr between clinopyroxene and melt could be influenced by crystallization kinetics.The depth of crystallization and differentiation of the basalts can be estimated from Ti and Al contents of clinopyroxene phenocrysts. From a combination of data on clinopyroxene composition, compatible trace element contents and mg-values of the rocks, it is concluded, that the alkali basalts of Pauliberg and Steinberg underwent slight olivine and clinopyroxene fractionation in shallow magma chambers prior to eruption, while the nephelinite of Stradnerkogel evolved mainly through clinopyroxene fractionation under high pressure conditions, probably in the upper mantle.

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Chemie der Pyroxene und Entwicklung von Alkalibasalten aus dem Burgenland und der Steiermark, Österreich

Zusammenfassung Einige pliozäne alkalibasaltische Gesteine aus dem Burgenland und der Steiermark wurden mineral-chemisch untersucht, um Aufschluß über ihre Evolution vor der Eruption zu erhalten. Klinopyroxene mit ihren vielfältigen Subtitutionsmöglichkeiten erlauben am besten eine Abschätzung der Evolution der Basalte. Pyroxen-Einsprenglinge der Basalte zeigen sowohl konzentrischen als auch sektoralen Zonarbau. Die von uns untersuchten Einsprenglinge zeigen in den verschiedenen Sektoren nicht nur unterschiedliche Gehalte an Ti, Al und Fe, sondern vielfach auch unterschiedliche Cr-Gehalte. Dies macht es wahrscheinlich, daß die Verteilung von Cr zwischen Klinopyroxen und Schmelze von der Kristallisations-Kinetik beeinflußt wird.Die Tiefe in der die Basalte kristallisierten und differenzierten kann von den Ti- und Al-Gehalten der Klinopyroxen- Einsprenglinge abgeschätzt werden. Die Zusammensetzung der Klinopyroxene im Verein mit den Gehalten an kompatiblen Spurenelementen und denmg-Werten der Gesteine erlauben den Schluß, daß die Alkalibasalte von Pauliberg und Steinberg vor ihrer Eruption eine geringfügige Olivinund Klinopyroxen-Fraktionierung in einer seichten Magmakammer erlebten. Der Nephelinit vorn Stradnerkogel hingegen erfuhr hauptsächlich eine Klinopyroxen Fraktionierung unter Hochdruck-Bedingungen, möglicherweise im oberen Erdmantel.

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With 8 Figures     

Geochemistry of newly discovered quaternary Shiribeshi Volcano,Northeast Japan Sea

Summary Shiribeshi Seamount is located to the east of the Okushiri Ridge, in the northeast Japan Sea. Whole rock K-Ar age of olivine-augite andesite dredged from the Seamount was determined to be 0.9 ± 0.2 Ma (Tsuchiya et al., 1989), indicating that Shiribeshi Seamount is a Quaternary volcano in the back-arc region off the junction of the Northeast Japan and Kurile arcs. Shiribeshi volcano is composed of basalt to rhyolite, which show a typical island arc calc-alkaline nature on the basis of petrographical characteristics of 95 samples dredged from four sites. Abundances of incompatible elements including K, Rb, Sr, Nb, P, Ti, Y and Zr in 16 representative rocks are discussed, together with those in the Quaternary volcanic rocks from the NE Japan and Kurile arcs in terms of compositional variation across the arcs. The estimated composition of the primary magma of Shiribeshi volcano is characterized by higher incompatible element contents and a higher Zr/Y ratio than primary magmas in the volcanic front side. Based on HFS element concentrations the degree of partial melting for three primary magmas of Oshima-Oshima, Shiribeshi and Rishiri volcanoes in the northeast Japan Sea may decrease gradually with increasing distance from the volcanic front. However, LIL element contents, especially K and Rb are lower in the primary magma of Rishiri volcano located far from the volcanic front than in the remaining two primary magmas, which would imply that LIL/HFS ratios (or degree of contribution of LIL elements originating from the subducted oceanic crust) become minimal at Rishiri volcano. One basalt and three andesites from Shiribeshi volcano have the restricted range of low⁸⁷Sr/⁸⁶Sr ratios of 0.70297–0.70300, which indicates that the magma source for Shiribeshi volcano may be slightly more enriched in Sr isotopic compositions than theN-type MORB source.

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Geochemie des neuentdeckten quartären submarinen Vulkans Shiribeshi im Nordöstlichen Japanischen Meer

Zusammenfassung Der Shiribeshi Seamount liegt östlich des Okushiri Rückens im nordöstlichen Japanischen Meer. Gesamtgesteins K-Ar Alter von Olivin-Augit-Andesiten von diesem Seamount ergeben Werte von 0,9 ± 0,2 Ma (Tsuchiya et al., 1989), und weisen darauf hin, daß Shiribeshi ein quartärer Vulkan im back-arc Bereich nahe dem Kreuzungspunkt des nordostjapanischen und des Kurilen-Inselbogens ist. Er besteht aus Gesteinen, deren Zusammensetzung von Basalt bis Rhyolit reicht. Petrographische Daten von 25 Proben, die von vier submarinen Lokationen durch Dredging aufgesammelt wurden, weisen auf eine typische kalk-alkalische Inselbogenzusammensetzung hin. Die Verbreitung von inkompatiblen Elementen, die unter anderem K, Rb, Sr, Nb, P, Ti, Y und Zr umfassen, in 16 representativen Proben wird zusammen mit denen von quartären vulkanischen Gesteinen aus dem nordöstlichen Japanischen und den Kurilen-Inselbogen diskutiert; dabei wird Variationen der Zusammensetzung über die Bögen hinweg besondere Beachtung geschenkt. Die so ermittelte Zusammensetzung des primären Magmas des Shiribeshi Vulkans wird durch höhere inkompatible Elementgehalte und höhere Zr/Y Verhältnisse charakterisiert, wenn man sie mit primären Magmen an der vulkanischen Stirn des Inselbogens vergleicht. HFS Element-Konzentrationen lassen erkennen, daß der Grad teilweiser Aufschmelzung für drei primäre Magmen von Oshima-Oshima, Shiribeshi und Rishiri im nordöstlichen Japanischen Meer graduell mit zunehmender Entfernung von der vulkanischen Stirm abnimmt. Die Gehalte an LIL Elementen und besonders an K und Rb sind in dem primären Magma des Rishiri Vulkans, der weit von der vulkanischen Front entfernt liegt, höher als in den zwei anderen primären Magmen. Dies weist darauf hin, daß LIL/HFS Verhältnisse (oder der Beitrag von LIL Elementen, die aus subduzierter ozeanischer Kruste stammen) am Rishiri Vulkan ein Minimum erreichen. Ein Basalt und drei Andesite von Shiribeshi zeigen⁸⁷Sr/⁸⁶Sr Verhältnisse von 0,70297 bis 0,70300; dies läßt erkennen, daß die Quelle des Magmas für Shiribeshi etwas mehr an⁸⁷Sr angereichert war, als dieN-Typ Quelle.

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With 7 Figures     

Desertification,famine, and the 1988 rainfall —

The 1988 good rainy season in the Sudan raised the hopes that desertification/land degradation and shortage of food so markedly observed in Western Sudan have been elevated. This was particularly so as large quantities of grains were produced in the mechanized rain-fed agricultural schemes in the clay plains of Eastern Sudan. But the field work carried by the author in the Umm Ruwaba district of Kordofan region in July/August 1989 shows that, although there has been some improvement in the crop production situation, desertification/land degradation and shortage of food produced locally are still prevailing in the district. The people are still living below the poverty line, but they are able to cope because of remittances from members of the families working abroad and because of donations of food by some world organizations.     

Stress-strain fields at the tunnelling face—Three-dimensional analysis for two-dimensional technical approach

Summary For tunnelling in rock, the original stress field in the ground is changed considerably before a first lining is participating in stabilizing the opening. Depending on this stress release at the tunnel face, only a small portion of the primary stresses is acting on the lining. Only a three-dimensional approach is able to determine the stresses and the deformations of the ground and the lining realistically. The paper presents some results of elastic three-dimensional finite-element-analyses in consecutive steps of the sectional excavation of circular and non-circular tunnels. From these results an equivalent two-dimensional approach is derived for technical applications, given in diagrams.     

A method for constructing toxic waste site histories from old airphotos of coastal regions

Archive aerial photos have been used to create a skeletal history for several toxic waste sites currently under investigation in the United States. Because many of the sites are very small in area, and the majority of the historical aerial photography is not large scale, specialized methods have, through experience, been developed to do this work. The result of the work is a series of standard format film stereograms and a detailed report. The report includes several unique methods for presenting the airphoto findings.     

Granulometric and mineral composition of the loess-paleosol formation in Moldova

The granulometric composition and sorting of loesses and interbedded soils are studied for stratigraphic subdivision and correlation of the loess-paleosol sequence in Moldova. Distinctive features of loess and paleosol horizons of different age are identified and general characteristics of the mineral composition are described that together with other lithological characteristics, including the visual ones, improve reliability of stratigraphic operations.     

7th World Congress on water resources Rabat,Morocco, 13–18 May, 1991

Submitted to United Nations Environment Programme Nairobi, Kenya by International Water Resources Association.     

Density and pressure change in an occluding cyclone

Summary On October 20, 1974, an occluding cyclone, which did not intensify any more crossed central Europe. Considerable pressure tendencies reflecting the displacement of the storm were observed during its passage. Although horizontal density advection contributed least to density and thus pressure changes, it was still of decisive importance for both. The other larger contributors, whose net effect was usually opposed to the effect of horizontal advection, nearly cancelled each other. Thus there was a fair correlation between horizontal advection and density tendency, and the actual density and pressure changes frequently turned out smaller than if caused by advection alone.It has been shown that in the lowest 3 km usually. For the mass divergence this inequality was observed in the frontal zones where horizontal advection was considerable. In particular, warm air advection reduced the effect of horizontal velocity convergence near the warm front. Thus, vertical mass divergence became predominant and caused a density decline. Cold air advection accompanying the cold front was responsible for horizontal divergence to be overcompensated by vertical mass convergence which induced rising density.With 11 Figures     

The effect of moist layer location on the stability of trapped gravity waves in an almost saturated atmosphere

Summary The stability characteristics of trapped gravity waves, generated by an isothermal bounded tanh (z) velocity profile in the presence of a saturated finite layer, are studied. The saturated layer is introduced at different levels above the inlection point and the variations of moisture content, layer thickness and distance from the origin are examined. The growthyrates and phase speeds of the unstable modes are obtained by solving numerically the equations of motion in the linear, inviscid, Boussinesq limit, via the technique of Lalas and Einaudi (1976).It is shown that the presence of the saturated layer can significantly affect the stability characteristics of the waves. inereases in moisture, layer thickness and distance of the layer from the inflection point are found to amplify the wave response because the saturated layer behaves as a top boundtry to the shear flow. The presence of such effective boundaries is found to stabilize short wavelengths and destabilize longer wavelengths. Finally, an application of the results to a rainband case produces values of the wave parameters in good agreement with the observed ones.With II Figures