645 research outputs found
Michael Bergmann, Michael J. Murray, Michael C. Rea (éd.), Divine Evil ? The Moral Character of the God of Abraham, Oxford, Oxford University Press, 2013
No full textHunziker-Rodewald Regine. Michael Bergmann, Michael J. Murray, Michael C. Rea (éd.), Divine Evil ? The Moral Character of the God of Abraham, Oxford, Oxford University Press, 2013. In: Revue d'histoire et de philosophie religieuses, 94e année n°3, Juillet-Septembre 2014. p. 326
Michael Bergmann, Michael J. Murray, Michael C. Rea (éd.), Divine Evil ? The Moral Character of the God of Abraham, Oxford, Oxford University Press, 2013
No full textHunziker-Rodewald Regine. Michael Bergmann, Michael J. Murray, Michael C. Rea (éd.), Divine Evil ? The Moral Character of the God of Abraham, Oxford, Oxford University Press, 2013. In: Revue d'histoire et de philosophie religieuses, 94e année n°3, Juillet-Septembre 2014. p. 326
Age and degree of metamorphism and time of nappe emplacement along the southern margin of the Damara Orogen/Namibia (SW-Africa)
No full textThe structure of articular cartilage
No full texthttp://www.woodheadpublishing.com/en/book.aspx?bookID=148
Migration of Folding and Metamorphism in the Rheinische Schiefergebirge Deduced from K-Ar and Rb-Sr Age Determinations
No full textn the very low- to low-grade metamorphic Rhenohercynian Zone of the Variscides a migration of folding has been postulated which was deduced from the shifting of flysch sedimentation.
In order to get an idea of the time span which the “wave” of folding and metamorphism has needed to pass through the Rheinische Schiefergebirge, isotopic investigations by K-Ar and Rb-Sr methods were carried out. For these measurements the fine mineral fractions <2μm from pure sericite slates probably derived from acid to intermediate glass-tuffs were analyzed. Furthermore extremely fine-grained sericite- and celadonite-bearing tuffs were taken which probably belong to the Middle Devonian volcanism.
Because of the very low degree of metamorphism in the Rheinische Schiefergebirge it can be assumed, that the blocking temperatures for the K-Ar and Rb-Sr systems of white micas were not exceeded — except for the K-Ar system in the “Taunus-Pre-Devonian”. Therefore most of the age determinations are indicative of the peak of metamorphism.
A determination of the age of folding was only possible on the proved assumption that:
The metamorphism is syntectonic with respect to folding. Therefore a determination of the metamorphic ages includes the determination of the age of folding.
The samples used for the isotopic investigations were not allowed to contain old sedimentary — not recrystallized — white micas. Only rock samples containing phyllosilicate fabrics of metamorphic origin were selected.
According to the K-Ar and Rb-Sr age determinations the age of metamorphism and folding in the Rheinische Schiefergebirge decreases from about 330 Ma in the Taunus towards the north to 300 Ma at the northern border.
Three exceptions modify this evolutionary history from the south to the north:
Lower ages in the “Taunus-Pre-Devonian” rocks have to be interpreted as cooling ages because the temperatures in this area exceeded the blocking temperature for the K-Ar system of the micas during metamorphism.
Higher ages in the Lahn Syncline of about 330 to 340 Ma which belong to rocks emplaced into their present position by nappe movement from the southern margin of the Schiefergebirge. They therefore preserved the higher metamorphic ages of the southern margin.
The high K-Ar age of about 340 Ma at the northern margin of the Schiefergebirge is interpreted as an influence of the North European Caledonian orogeny.
The synmetamorphic “wave” of folding passed through the Rheinische Schiefergebirge from the northern border of the Mid-German Crystalline Rise to the present northern border in approx. 30 Ma. This would correspond to a “velocity of crustal shortening” of about 0,5 cm/year, if one assumes a mean tectonic shortening of about 50% in the Rheinische Schiefergebirge resulting from compression during deformation. These values have to be regarded as minimum values
Magma generation at the easternmost section of the Hellenic arc: Hf, Nd, Pb and Sr isotope geochemistry of Nisyros and Yali volcanoes (Greece)
No full textGeochemical and petrographical studies of lavas and ignimbrites from the Quaternary Nisyros–Yali volcanic system in the easternmost part of the Hellenic arc (Greece) reveal insight into magma generating processes. A compositional gap between 61 and 68 wt.% SiO2 is recognized that coincides with the stratigraphic distinction between pre-caldera and post-caldera volcanic units. Trace element systematics support the subdivision of Nisyros and Yali volcanic units into two distinct suites of rocks. The variation of Nd and Hf present day isotope data and the fact that they are distinct from the isotope compositions of MORB rule out an origin by pure differentiation and require assimilation of a crustal component. Lead isotope ratios of Nisyros and Yali volcanic rocks support mixing of mantle material with a lower crust equivalent. However, 87Sr/86Sr ratios of 0.7036–0.7048 are incompatible with a simple binary mixing scenario and give low depleted mantle extraction ages (<0.1 Ga), in contrast with Pb model ages of 0.3 Ga and Hf and Nd model ages of ca. 0.8 Ga. The budget of fluid-mobile elements Sr and Pb is likely to be dominated by abundant hydrous fluids characterised by mantle-like Sr isotope ratios. Late stage fluids probably were enriched in CO2, needed to explain the high Th concentrations. The occurrence of hydrated minerals (e.g., amphibole) in the first post-caldera unit with the lowermost 87Sr/86Sr ratio of 0.7036±2 can be interpreted as the result of the increased water activity in the source. The presence of two different plagioclase phenocryst generations in the first lava subsequent to the caldera-causing event is indicative for a longer storage time of this magma at a shallower level. A model capable of explaining these observations involves three evolutionary stages. First stage, assimilation of lower crustal material by a primitive magma of mantle origin (as modelled by Nd–Hf isotope systematics). This stage ended by an interruption in replenishment that led to an increase of crystallization and, hence, an increase in viscosity, suppressing eruption. During this time gap, differentiation by fractional crystallization led to enrichment of incompatible species, especially aqueous fluids, to silica depolymerisation and to a decrease in viscosity, finally enabling eruption again in the third stage
Palaeobotanical and geochronological evidence for the Alpine age of the metamorphism in the Sesia-Zone
No full textDas Alter der letzten Metamorphose der Sesia-Zone wurde lange Zeit für herzynisch oder älter gehalten. Als Argument dienten Grundgebirgseinschlüsse in den Trachyandesiten bis Andesiten der Sesia-Zone. Diese Vulkanite hielt man in Analogie zu den permischen Vulkaniten der Südalpen für permisch. In jüngster Zeit wurden in Tuffiten der Sesia-Vulkanite Pflanzenreste gefunden, die als oberkarbonisch beschrieben wurden. Diese Schlüsse standen in Diskrepanz zu strukturgeologischen Beobachtungen und zu den zahlreichen radiometrischen Altersbestimmungen in der Sesia-Zone und zwangen zur nochmaligen überprüfung der paläobotanischen Evidenzen. Die von uns gefundene Flora weist sehr moderne Züge auf und läßt sich mit Sicherheit ins Tertiär einstufen. Kein einziges paläozoisches Fossil wurde gefunden. Das durch die Pflanzenreste bestätigte tertiäre Alter der Vulkanite konnte mit radiometrischen K-Ar-Gesamtgesteinsaltern auf 29–33 m.y. präzisiert werden. Die letzte Hochdruck-Metamorphose in der Sesia-Zone fand nach K-Ar-Altersbestimmungen an Glimmern zwischen 60 und 90 m. y. statt. Vor ca. 38 m. y. wurden die alpeneinwärts liegenden Partien der Sesia-Zone von der lepontinischen Kristallisationsphase in Grünschieferfazies überprägt.For a long time the age of the last metamorphism of the Sesia-zone was considered to be Hercynian or older. Basement inclusions in basic volcanics were the main argument for this interpretation. The Trachyandesites — Andesites of the Sesia-zone were regarded as Permian, analogoues to the widespread Permian volcanics of the Southern Alps. Recently, plant remnants have been found in tuffitic interlayers of the Sesia volcanics. These fossils have been described as palaeozoic plants, in contradiction to structual observations and to the numerous radiometric data acquired in the region. To check the age of the fossils a detailed palaeobotanical study was carried out. Our samples contained a very modern flora of definitely Tertiary age. Not one palaeozoic fossil was detected. The Tertiary age found on palaeobotanical evidence proved to be between 29 and 33 m. y. on the basis of total rock K-Ar ages. The last high pressure metamorphism of the Sesia-zone occurred between 90 and 60 m. y. as has been shown by radiometric ages on micas. The external part of the zone was overprinted by the Lepontine phase of metamorphism in greenschist facies 38 m. y. ago
Sylvie Donnat; Régine Hunziker-Rodewald i Isabelle Weygand (eds.), Figurines féminines nues. Proche-Orient, Égypte, Nubie, Méditerranée orientale, Asie centrale (VIIIe millénaire av. J.-C.- Ive siècle ap. J.-C.). Actes du colloque de Strasbourg (25-26 juin 2015). Collections de l'Université de Strasbourg, Études d'archéologie et d'histoire ancienne. Éditions de Boccard, París, 2020, 360 p.ISBN: 978-2-7018-0532-0; ISSN: 1284-6325
No full textSylvie DONNAT; Régine HUNZIKER-RODEWALD i Isabelle WEYGAND (eds.), Figurines féminines nues. Proche-Orient, Égypte, Nubie, Méditerranée orientale, Asie centrale (VIIIe millénaire av. J.-C.- Ive siècle ap. J.-C.). Actes du colloque de Strasbourg (25-26 juin 2015). Paris: Éditions de Boccard, 202
Carbon Isotope stratigraphy and carbonate productivity during the Early-Middle Jurassic: examples from the Umbria-Marche-Sabina Apennines (Central Italy)
No full textAbstract: The carbon isotopic signature of carbonates depends on secular variations of organic carbon and carbonate carbon production/burial rates. A decrease in carbonate productivity makes the organic/carbonate carbon ratio unstable up to the point that even minor variations in the organic carbon reservoirs can provoke carbon isotopic shifts. The delta(13)C positive shifts of the middle Carixian (early Pliensbachian) and the early Bajocian recorded in the Umbria-Marche-Sabina domain represent a good example of this mechanism. Both sedimentology and lithostratigraphy of pelagic platform-basin carbonate systems in this area show that important changes in the source of carbonates correspond to the observed isotopic shifts. The middle Carixian event is in fact well correlatable to the drastic reduction of benthic carbonate production on rift-related intrabasinal highs, which then became pelagic carbonate platforms. The early Bajocian event is concomitant with the beginning of a long hiatus on the pelagic carbonate platforms and with a drop of the biodiversity of calcareous organisms followed by the onset of biosiliceous sedimentation in basins. (C) 2002 Elsevier Science B.V. All rights reserved
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