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  • 1
    ISSN: 1432-0495
    Keywords: Keywords factor analysis ; Genoa ; geochemical mapping ; mercury ; stream sediment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Systematic stream sediment investigation in a periurban area surrounding Genoa (Italy) revealed the existence of a significant mercury anomaly localized on the main (3rd rank) bed of the Bisagno river. Statistical multivariate analysis of elemental abundances points out the anthropic nature of this contamination. Because of the well-known bioaccumulation of Hg in contaminated media, attention must be focused on the risks associated with the discovered pollution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Analytica Chimica Acta 82 (1976), S. 415-420 
    ISSN: 0003-2670
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 304 (1991), S. 703-706 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Nuclear Instruments and Methods in Physics Research Section A: 296 (1990), S. 568-573 
    ISSN: 0168-9002
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    The @Journal of Chemical Thermodynamics 19 (1987), S. 809-818 
    ISSN: 0021-9614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract New data on major and trace elements geochemistry of the Assab Range (Ethiopia) basalts and enclosed mantle xenoliths are presented and discussed. Mantle ultramafics consist of spinel-peridotites and minor green spinel-pyroxenites (sometimes present as dykes within the former ones). Petrography and mineral chemistry indicate that both xenoliths families underwent a common subsolidus equilibrium crystallization at 1050°–1100° C., in the spinel-peridotite stability field. REE data on whole rock and on separated phases (cpx, opx and ol) have been obtained by RNAA. Spinel-peridotites exhibit LREE-enriched — HREE-depleted patterns with respect to chondrites. Mass balance calculations indicate that this is a characteristic feature of spinel-peridotite xenoliths which cannot be solely imputed to host basalt contamination. Xenoliths selected as representative of different depletion intensities, suffered by Assab spinel-peridotites prior to their subsolidus equilibration, show dependences from major elements composition in their REE geochemistry and wide variations in the measured REE partition values among coexisting phases. Concordancy in the REE compositions of liquids calculated utilizing the measured REE partitioning in the different xenoliths and theShaw's (1970) mass balance equation for non-modal equilibrium melting, confirms that the measured REE distribution represent equilibrium conditions. Theoretical least fusion liquids differ from the least differentiated among the enclosing basalts, both in their La/Lu ratio and in the total REE concentrations. Some similarities are observed with the composition of the pyroxenite dykes, however no firm conclusions on the comagmaticity of the two xenoliths types are reached. Trace geochemistry (REE, Ba, Sr, Cs, Rb, U, Th, Hf, Zr, Ta, Sc, Cr, Co, Ni: RNAA, INAA) on the host basalts indicates that the primary alkaline melts underwent an indipendent differentiation history by fractional crystallization at intermediate pressure conditions prior to the mantle xenoliths inclusion. Extrapolated seismic velocities for the Assab mantle xenoliths allow to ascribe them to the 7.3–7.7 VP layer, underlying the crustal layers in the Assab and Afar area, as recognized on the basis of the geophysical surveys. In light of the above evidences, an evolutive picture of the Assab association is proposed which takes into account present day knowledges on the geodynamic evolution of the Afar-Red Sea system.
    Abstract: Résumé Dans ce travail nous presentons des nouvelles données sur la géochimie des éléments majeurs et en traces dans les basaltes et dans les enclaves du manteau de la zone d'Assab (Éthiopie). Les enclaves; ultrabasiques du manteau sont constituées par des peridotites à spinelle et subordonnément par des pyroxenites à spinelle (quelquefois en forme de dykes dans les (peridotites). La pétrographie et la chimie des mineraux indiquent que les deux familles des enclaves esseurent une commune recristallization à l'équilibre aux temperatures de l'ordre de 1050°–1100° C dans le champ de stabilité de la peridotite à spinelle. Les données sur les terres rares dans la roche totale et dans les minéraux séparés ont été obtenues par RNAA. Les peridotites à spinelle montrent des patterns enrichis en terres rares légères et appauvries en terres rares lourdes par rapport à les aux condrites. Des calculs de balance de masse indiquent que cette caractéristique ne peut pas être attribuée simplément à la contamination par le basalte encaissant. Des enclaves sélectionées comme residus des differentes intensités de fusion partielle montrent des relations simples entre éléments majeurs et la géochimie des terres rares et des importantes variations des coefficients de partage des terres rares entre les differentes mineraux coexistants dans le même enclave. D'ailleurs la concordance entre les compositions en terres rares des differents liquides calculés à partir de la distribution des terres rares entre les mineraux des differents enclaves (en utilisant la loi deShaw, 1970) montre que les distributions mesurées sont representatives des conditions d'équilibre. Les liquides théoriques de fusion minime ont des valeurs differentes La/Lu et des teneurs differentes en terres rares par rapport à les laves aux encaissantes. Par contre quelque similitude peut-être envisagée avec les pyroxenites cependant les données actuelles ne permettent pas de rejoindre des conclusions sur la comagmaticitée des deux familles des enclaves. La géochimie des traces (REE, Ba, Sr, Cs, Rb, U, Th, Hf, Zr, Ta, Sc, Cr, Co, Ni: RNAA, INAA) sur les laves encaissantes montre que le magma alcalin primaire a differencié par cristallization fractionnée à des conditions de pression intermediaire avant d'encaisser les enclaves du manteau. Les vitesses seismiques déduites pour les enclaves du manteau à partir des données experimentales permettent d'identifier ces matériaux avec la couche à vitesse VP=7.3 –7.7 sous la région d'Assab et de l'Afar. Un modèle evolutif de l'association étudiée est presenté tout en considérant les conaissances actuelles de l'evolution geodinamique du sytème Afar-Mer Rouge.
    Notes: Zusammenfassung Die ultrabasischen Gesteine des Mantels der Zone Assab (Äthiopien) bestehen aus Spinell-Peridotiten und aus wenigen grünen Spinell-Pyroxeniten (manchmal sind sie in Form von Intrusivgängen in den Spinell-Peridotiten). Die Petrologie und die Mineralchemie zeigen, daß die zwei Xenolith-Familien eine gemeinsame Rekristallisation unter Gleichgewicht bei den Temperaturen 1050°–1100° C im Stabilitäts-Feld der Spinell-Peridotite hatten. Die Daten über die Seltenen Erden im Gesamtgestein und die getrennten Mineralien (cpx, opx und 01) wurden mit der RNAA-Methode erhalten. Die Spinell-Peridotite zeigen eine Anreicherung an leichten Seltenen Erden und eine Verarmung an schweren Seltenen Erden in Beziehung auf die Chondrite. Die Berechnungen der Massengleichgewichte zeigen an, daß dies eine Charakteristik von Spinell-Peridotit-Xenolithen darstellt, die nicht auf eine Verunreinigung durch die umgebenden Basalte zurückgeführt werden darf. Xenolithe aus verschiedenen Stadien der Aufschmelzung zeigen einfache Beziehungen zwischen Hauptelementen und der Geochemie der Seltenen Erden und weite Variationen der Verteilungs-Koeffizienten der Seltenen Erden unter koexistenten Phasen. Die Geochemie der Spurenelemente (REE, Ba, Sr, Cs, Rb, U, Th, Hf, Zr, Ta, Sc, Cr, Co, Ni: RNAA, INAA) in den Basalten zeigt, daß sich das primäre, alkalische Magma durch fraktionierte Kristallisation differenziert hat bevor die Peridotiteinschlüsse auftraten. Diese Beobachtungen stehen im Einklang mit der modernen Erkenntnis über die geodynamische Entwicklung der Afar-Region und des Roten Meeres.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 46 (1990), S. 160-165 
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Contributions to mineralogy and petrology 111 (1992), S. 53-60 
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract Excess Gibbs free energy surfaces generated at various pressure and temperature conditions for the C2/c pyroxene quadrilateral compositional space Mg2Si2O6−CaMgSi2O6−CaFeSi2O6−Fe2Si2O6 with a two-body static interionic potential summation (Ottonello et al. 1992) have been fitted to 4 component extensions of the Wohl and Kohler macroscopic interactions models. The mean precision (272j/mol) and the maximum observed bias (1.19 Kj/mol) are roughly similar for the two macroscopic formulations, but Wohl's extension is preferred due to its relative simplicity.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Physics and chemistry of minerals 17 (1990), S. 301-312 
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Single-crystal X-ray structure refinement of natural olivines equilibrated at high temperature under controlled oxygen fugacity (f O2) conditions, coupled with a structure-energy model were used to establish the influence of T, f O2 and bulk chemistry on intracrystalline disorder. The results are: 1) The k D (k D = [(Fe M1·Mg M2)/(Fe M2·Mg M1)]) factor describing site population on M1, M2 polyhedra increases from values lower than 1 at T below 400–600° C (depending on composition) to values higher than 1 at higher temperature. 2) The increase of k D with T is quite regular. 3) At constant temperature and pressure, k D increases with increasing fayalite content in the mixture; 4) Contrary to previous observations (Will and Nover 1979; Nover and Will 1981) varying f O2, within the stability range of the substance, has a negligible influence on intracrystalline disorder. 5) As ancillary results, the model confirms the defect scheme of Nakamura and Schmalzried (1983) for the investigated solids. Moreover, it shows that cationic vacancies are always created on M 1 site at the expense of Mg ions, while trivalent iron is always stabilized on M2 site. This explains the marked anisotropies observed in Fe-Mg interdiffusion (Buening and Busek 1973; Misener 1974; Schock et al. 1989).
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Neurological sciences 19 (1998), S. S25 
    ISSN: 1590-3478
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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