Eocene high pressure metamorphism in the Penninic units of the Tauern Window (Eastern Alps); evidence from 40Ar-39Ar dating and petrological investigations

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Authors:Zimmermann, R.; Hammerschmidt, K.; Franz, G.
Author Affiliations:Primary:
Technical University Berlin, Department of Petrology, Berlin, Federal Republic of Germany
Federal University Institute for Mineralogy, Federal Republic of Germany
Volume Title:Contributions to Mineralogy and Petrology
Source:Contributions to Mineralogy and Petrology, 117(2), p.175-186. Publisher: Springer International, Heidelberg-New York, International. ISSN: 0010-7999
Publication Date:1994
Note:In English. 52 refs.; illus., incl. 3 tables, geol. sketch maps
Summary:The 40Ar/39Ar degassing spectra of white micas and amphiboles from three tectonic units of the central Tauern Window (Pennine basement and cover in the Eastern Alps) have been measured. White micas are classified as: 1) pre-Alpine low-Si relict micas with an age value of 292 m.y., variously disturbed by the Alpine metamorphism; 2) Alpine phengitic micas of variable composition, with an age between 32 and 36 m.y.; 3) Alpine low-Si micas with a maximum age of 27 m.y. The higher Alpine ages are attributed to a blueschist-facies event, whereas the lower age reflects the late cooling of the nappe pile. Blueschist-facies phengites from the basement (Lower Schieferhulle) and the tectonic cover (Upper Schieferhulle) crystallized at a T between the closure T (Tc) for Ar diffusion in white mica and record ages of 32 to 36 m.y. At the same time a thin, eclogite-facies unit was thrust between the Lower and Upper Schieferhulle and cooled from eclogite-facies conditions at ∼ 600°C at 20 kbar to blueschist-facies conditions at 450 or even 300°C at >> 10 kbar. Eclogite-facies phengites closed for Ar diffusion and record cooling ages, coinciding with the crystallization ages in the hanging and the footwall unit. Amphibole age spectra (actinolite, glaucophane, barroisite) are not interpretable in terms of geologically meaningful ages because of excess Ar. [P. Br.]
Subjects:Absolute age; Ar-40/Ar-39; Ar/Ar; Argon; Blueschist facies; Cenozoic; Chemical composition; Dates; Eclogite facies; Eocene; Facies; High-grade metamorphism; Isotopes; K/Ar; Metamorphism; Mica group; Muscovite; Noble gases; P-T conditions; Paleogene; Phengite; Radioactive isotopes; Sheet silicates; Silicates; Stable isotopes; Tertiary; Upper Eocene; Alps; Austria; Central Alps; Central Europe; Eastern Alps; Europe; Pennine Alps; Tauern Window
Abstract Numbers:95M/26
Record ID:1995027064
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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