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  • 1
    Electronic Resource
    Electronic Resource
    The effects of ferromagnesian components on the paragonite-muscovite solvus: a semiquantitative analysis based on chemical data for natural paragonite-muscovite pairs (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of metamorphic geology 12 (1994), S. 0 
    Details
    ISSN: 1525-1314
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Chemical data for 139 natural paragonite-muscovite (Pg-Ms) pairs illustrate the effects of ferromagnesian components on the P-T-X topology of the Pg-Ms solvus. The pairs were selected on the basis of: reasonably accurate knowledge of the P-T conditions of formation; evidence for close approach to equilibrium at peak metamorphic conditions; exclusion of pairs in which paragonite contains more than 5 mol% margarite; and exclusion of pairs from polymetamorphic rocks that contain more than one set of cogenetic Pg-Ms pairs. Graphical analysis reveals considerable scatter in the data; nevertheless, it is evident that the muscovite limb of the solvus shifts markedly toward end-member muscovite with increasing pressure from approximately 7 kbar to 21 kbar. This shift is attributed to a pressure-induced increase of the ferromagnesian content of muscovite, which increases the size of the XII alkali site - to the effect that K is more readily accommodated than Na. The data also suggest that the paragonite limb of the solvus migrates slightly toward end-member paragonite with increasing pressure. Broadening of the Pg-Ms solvus with increasing pressure reflects increasingly nonideal Na-K mixing as the phengite content of muscovite increases. Due to the wide scatter of data for Pg-phengitic-Ms pairs, it is concluded that, at the present time, Pg-Ms solvus thermometry is only viable for quasibinary Pg-Ms pairs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1525-1314.1994.tb00059.x
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  • 2
    Electronic Resource
    Electronic Resource
    The b 0 value of the potassic white micas as a barometric indicator in low-grade metamorphism of pelitic schists (1974)
    Springer
    Contributions to mineralogy and petrology 45 (1974), S. 143-152 
    Details
    ISSN: 1432-0967
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract The b 0 of the potassic white micas was measured in 410 samples of low-grade pelitic schists from the Central Pyrenees, the Abukuma belt, Northern New Hampshire, the Eastern Alps, Otago, the Sanbagawa belt and the Central Pontic Chain. Temperature and rock bulk composition can be considered substantially constant all over the sample range, so that the differences in the b 0 values depend primarily on differences in pressure. The analytical data demonstrate that the b 0 increases for increasing pressure, and that it is practically identical in the micas from very different regions belonging to the same baric type of metamorphism. With the help of other analytical data (about 600), a b 0 scale was prepared, which makes the distinction of six different facies series possible. The writers, proposing this very rapid new method of barometric analysis, draw attention to its limitations and point out the main fields of its application.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00371166
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  • 3
    Electronic Resource
    Electronic Resource
    The petrological and geological significance of theb 0 values of potassic white micas in low-grade metamorphic rocks. An application to the Eastern Alps (1972)
    Springer
    Mineralogy and petrology 18 (1972), S. 105-113 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Résumé Dans les Alpes orientales les valeursb 0 des micas blancs potassiques des schistes épimétamorphiques d'age hercynien diffèrent nettement de celles de roches isogrades et isochimiques d'age alpin. Ges différences, qui indiquent des variations de la quantité de phengite présente en solution solide dans les micas blancs, sont référables à différences de pression. Par cette méthode on a reconnu, dans les schistes épimétamorphiques appartenant à de différentes unités tectoniques des Alpes orientales, le caractère alpinotype du métamorphisme morphisme hercynien, et d'autre part le caractère alpinotype du métamorphisme alpin; cette distinction est impossible à faire à faire à l'aide des méthodes traditionelles, à cause de l'absence de minéraux caractéristiques dans les schistes épimétamorphiques. Les résultats de cette étude ont permis d'établir que, au cours de l'analyse des complexes épimétamorphiques, les mesures deb 0 peuvent fournir des données précieuses qu'à présent il est impossible d'obtenir autrement. Ces recnées sont utiles soit pour évaluer la pression de recrystallisation, soit pour reconnaître l'age du métamorphisme.
    Notes: Summary In the Eastern Alps theb 0 values of potassic white micas of Hercynian low-grade schists differ sharply from those of Alpine isograde and isochemical rocks. These differences, which indicate variations in the phengite content present as solid solution in the white micas, are to be referred to differences in pressure. In this way it is possible to recognize, in the low-grade metamorphic rocks of different tectonic units of the Eastern Alps, the lowpressure character of the Hercynian metamorphism, and the higher-pressure character of the Alpidic thermic event; this recognition is not possible using traditional methods, owing to the lack of characteristic minerals in the lowgrade metamorphic rocks. The results of the present report allow us to state that generally, when studying low-grade metamorphic complexes, theb 0 measurements can supply valuable data which are not obtainable in any other way at the present time. These data are useful both for estimating recrystallization pressure and for recognizing the age of metamorphism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01081796
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  • 4
    Electronic Resource
    Electronic Resource
    Some thoughts on the pre-Alpine metamorphic history of the austridic basement of the Eastern Alps (1975)
    Springer
    Mineralogy and petrology 22 (1975), S. 175-199 
    Details
    ISSN: 1438-1168
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung An mehreren Stellen im altkristallinen Grundebirge der Ostalpen ist eine Gliederung der voralpidischen metamorphen Ereignisse in eine ältere Metamorphose, die einer hoch-bis mitteldruckbetonten Faziesserie (Eklogite, Disthen) angehört und eine jüngere weniger druckbetonte Metamorphose (Andalusit±Disthen±Cordierit) erkennbar. Einzelne lokale geologische Situationen erlauben eine scharfe chronologische Trennung dieser zwei Ereignisse; das Caledonische Alter (∼ 500m.y.) der älteren und das Hercynische Alter (∼ 320 m.y.) der jüngeren Metamorphose wird durch radiometrische Altersdaten demonstriert. Es gibt Hinweise, daß die Caledonische Metamorphose zu einem komplexen geologischen Ereignis mit allen Kennzeichen eines orogenen Zyklusses gehört, das im wesentlichen während des Ordoviziums stattgefunden hat. Diese genetischen Vorstellungen scheinen als mögliches Modell für die gesamten Ostalpen annehmbar.
    Notes: Summary In several places of the old crystalline basement of the Eastern Alps a classification of the pre-Alpine metamorphic effects into an older, high-to intermediate-pressure metamorphism (eclogites, kyanite) and a younger, lower-pressure one (and±ky±cord) is recognizable. Some local geological situations allow a sharp chronological distinction to be made between these two events; and the available radiometric age values demonstrate the Caledonian age (∼500 m.y.) of the older metamorphism and the Hercynian age (∼320 m.y.) of the younger one. Elements exist showing that the Caledonian metamorphism, belongs to a complex cycle of geological processes which took place substantially during the Ordivician age (?) and has all the “ingredients” of the orogenic cycles. This evolutional picture represents a possible model for the whole of the Eastern Alps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01087838
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  • 5
    Electronic Resource
    Electronic Resource
    On the age of the Vedrette di Ries (Rieserferner) massif and its geodynamic significance (1979)
    Springer
    International journal of earth sciences 68 (1979), S. 41-60 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Abstract The Rb/Sr whole rock method was used to carry out radiometric analyses on about forty samples from the Vedrette di Ries massif. The samples were arranged in five sample groups. The age of this massif was found to be Middle Oligocene, and the best-defined isochron (30±3 m. y.) was obtained with a group of nine samples from the Upper Anterselva Valley. The values of the initial Sr isotopic ratio range between 0.709 and 0.727. This fact suggests that these melts were the result of the anatexis of different crustal materials, with some contributions from components with low (87Sr/86Sr)i values. A genetic link is proposed between these Oligocene melts and the “Tauern metamorphism”.
    Abstract: Résumé Pour analyser radiométriquement environ quarante échantillons du massif de Riesenferner (Vedrette di Ries) on a employé la méthode Rb/Sr sur roche totale. Les échantillons ont été réunis en cinq groupes. Il en résulte que l'âge de ce massif remonte à l'Oligocène moyen. L'isochrone la meilleure (30±3 m.y.) a été obtenue avec un groupe de neuf échantillons provenant de la haute vallée d'Antholz (Anterselva). Les valeurs des rapports initiaux (87Sr/86Sr) se placent entre 0,709 et 0,727: Cela suggère que ces liquides ont été le résultat d'une anatexie portant sur différents matériaux de la croûte, avec contribution de composants à basses valeurs (87Sr/86Sr). On propose un lien génétique entre ces magmas de l'Oligocène et le métamorphisme des 〉Tauern〈.
    Notes: Zusammenfassung Für eine radiometrische Gesamtgesteinsanalyse von etwa vierzig Proben des Rieserferner-Massivs, hat man sich der Rb/Sr Methode bedient. Die Proben wurden in fünf Gruppen zusammengestellt. Daraus ergibt sich, daß das Alter dieses Massivs Mittel-oligozän ist. Die beste Isochrone (30±3 M. Jahre) wurde mit einer Gruppe von neun Proben, die aus dem oberen Antholzertal ergaben, erreicht. Die Werte der initialen Sr87/Sr86-Isotopenverhältnisse sind zwischen 0,709 und 0,727. Das regt zum Denken an, daß diese Schmelze das Ergebnis von Anatexis von verschiedenen Krustengesteinen mit der Hilfe von Komponenten mit niedrigen Werten (87Sr/86Sr); waren. Zwischen diesen Oligozänschmelzen und der Tauernmetamorphose wird eine genetische Bindung vorgeschlagen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01821121
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  • 6
    Electronic Resource
    Electronic Resource
    Outline of the Somalian basement (1981)
    Springer
    International journal of earth sciences 70 (1981), S. 882-896 
    Details
    ISSN: 1437-3262
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Description / Table of Contents: Zusammenfassung Eine Folge von Ereignissen, die sich in den zwei Basement-Regionen Somalias erkennen lie\en, wird auf der Basis neuer GelÄnde- und petrographischer Daten und früherer publizierter und nicht publizierter Berichte umrissen. Das Basement von Somalia entwickelte sich wÄhrend des Panafrikanischen Ereignisses. Viel Detailarbeit ist jedoch noch zu leisten, bis die Geschichte des Basements in das detailliertere Bild Panafrikas, wie es aus den Nachbarregionen gewonnen wurde, integriert werden kann.
    Abstract: Résumé Dans les deux régions de la Somalie ou le socle affleure, on a reconnu une succession d'événements sur la base de nouvelles données géologiques et pétrographiques et de travaux pré-existants, publiés et non publiés. L'évolution du socle de la Somalie se déroula pendant l'événement Pan-Africain. Toutefois, beaucoup de travail doit Être encore fait avant que l'histoire du socle somalien puisse Être intégrée dans un cadre Pan-Africain plus détaillé, tel qu'on le connait dans les régions voisines.
    Notes: Abstract A sequence of events which has been recognized in the two basement regions of Somalia is outlined on the basis of new field and petrographic data and pre-existing published and unpublished reports. The evolution of the Somalian basement took place during the Pan-African event, However, much detailed work is necessary before the history of the basement can be integrated into the more detailed Pan-African picture recognized in the neighbouring regions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01820169
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