Record details

Title
    A vestige of very high-pressure (ca 28 kbar) metamorphism in the Variscan Bohemian Massif, Czech Republic
Statement of responsibility
    Jana Kotková, Simon L. Harley, Milan Fišera
Author
    Fišera, Milan, 1937-
    Harley, Simon L.
    Kotková, Jana, 1963-
Language
    anglicky
Source title - serial
    European journal of mineralogy
Vol./nr.
    Vol. 9, no. 5
Pages
    p. 1017-1033
Year
    1997
Notes
    6 obr., 2 fot., 2 tab., 4 s.bibl.
    Zkr. název ser.: Eur. J. Mineral.
Subject group
    granátit
    granáty
    metamorfóza vysokotlaká
    moldanubikum jižních a jihovýchodních Čech
    ortopyroxeny
    podmínky P-T
    reakční obruba
    symplektit
    vrásnění variské
Geographical name
    ČR-Čechy
    Vítkov (Strakonice)
Keyword
    28
    Bohemian
    Ca
    Czech
    High-pressure
    Kbar
    Massif
    Metamorphism
    Republic
    Variscan
    Very
    Vestige
Abstract (in english)
   A unique Mg-Al rich rock from the Podolsko Complex of the South Bohemian Moldanubicum contains a relic assemblage of pyrope-rich garnet+low-Al orthopyroxene+quartz that implies very high-presure (VHP) conditions of metamorphism. Garnet-orthopyroxene thermobarometry yields relatively precise P-T estimates of 26+-3 kbar and 830+-30°C using the Harley (1984a) thermometer and Harley (1984b) barometer, or 28+-3kbar using the Harley & Green (1982) thermobarometer. These pressures are consistent with the absence of coesite relics or palisade quartz after coesite, which places an upper pressure limit of about 29 kbar at the estimated temperature. This VHP assemblage is extensively overprinted by symplectites and coronas. Orthopyroxene (XMg=0.74-0.78,5-7 wtAl2O3) and plagioclase (An45) form layered coronas between quartz and garnet.
   Garnet is now further replaced by fingerprint and filamentous symplectites involving sapphirine (XMg=0.80-0.81), orthopyroxene (XMg=0.72-0.76, 6-9 wtAl2O3), cordierite (XMg=0.90), and locally spinel. Highly resorbed garnet is zoned to much lower XMg (0.62-0.55) within 50-100 um of these symplectites, which formed at granulite-facies, pressure-temperature conditions of 8+-1.5 kbar and 800-900 C. Despite its demonstrably continental crustal origin the investigated Mg-Al-rich rock documents an initial phase of VHP metamorphism at pressures exceeding any estimates obtained so far for the crustal eclogites present in the Moldanubian Zone of the Bohemian massif, which are generally nearer 20 kbar
Contributor
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
    U
Entered date
    21. 2. 2008
Import date
    8. 8. 2012