Podrobnosti záznamu

Název
    Ultrahigh-pressure grossular-rich garnetite from the Moldanubian Zone, Czech Republic
Údaj o odpovědnosti
    Stanislav Vrána, Jiří Frýda
Autor
    Frýda, Jiří
    Vrána, Stanislav
Jazyk
    anglicky
Zdrojový dokument - seriál
    European journal of mineralogy
Svazek/č.
    Vol. 15, no. 1
Strany
    p. 43-54
Rok
    2003
Poznámky
    6 obr., 2 fot., 2 tab., 2 s. bibl.
    il.
    Zkr. název ser.: Eur. J. Mineral.
Předmětová skupina
    baryum
    chemismus minerálů
    eklogit
    epidot
    granátit
    granáty
    grosulár
    metamorfóza vysokotlaká
    moldanubikum západní Moravy
    sodík
    symplektit
Geografické jméno
    ČR-Morava
    Pucov (Třebíč)
Klíčové slovo
    Czech
    Garnetite
    Grossular-rich
    Moldanubian
    Republic
    Ultrahigh-pressure
    Zone
Abstrakt (anglicky)
   grossular-rich garnetite composed of 80 vol. per cent garnet (Grs63Alm25Prp7And4) and 15 vol. per cent hercynite+anorthite symplectite after kyanite occurs as a boudin in migmatitic gneiss of the Gfohl unit in the easternmost part of the Moldanubian Zone, next to its overthrust on the Cadomian foreland in Moravia, Czech Republic. Garnet cores contain 0.10 to 0.18 wt. per cent Na2O and up to 0.5 wt. per cent TiO2. Both rutile and ilmenite are present as early inclusions in garnet. The UHP assemblage underwent partial decompression breakdown under granulite/amphibolite facies conditions, including the reaction garnet + kyanite - hercynite + anorthite (An99) and localised reaction of garnet to anorthite+aluminous augite+ferropargasite+titanite veinlets. A Ba-Al-Fe silicate loosely related to bafertisite is a minor phase tied to anorthite aggregates. The widespread preservation of Na-rich garnet indicates that Na diffusion was controlled by the limited extent of decompression reactions.
   The elevated sodium content in garnet, comparable to those of diamond-bearing UHP crustal rocks and diamondiferous eclogites, indicates imprint of sub-lithospheric high pressures, P = 4 GPa. The garnetite can be interpreted as a calc-silicate rock subducted to mantle depths and subsequently obducted with mantle peridotite and pyroxenites. This scenario is supported by published isotopic evidence on a Palaeozoic crustal component in some mantle-derived Variscan garnet pyroxenites and eclogites in the Gföhl unit. Very close similarity of garnetite composition to epidote (except Fe oxidation state and H2O content) indicates that a nearly monomineralic epidosite is the most probable parent rock
Přispěvatel
    Česká geologická služba
Kód přispěvatele
    ČGS (UNM)
Zdrojový formát
    U
Datum vložení
    15. 8. 2007
Datum importu
    8. 8. 2012