Podrobnosti záznamu

    Melting in high-P region - case of Bohemian granulites
Údaj o odpovědnosti
    Petr Jakeš
    Jakeš, Petr, 1940-2005
Zdrojový dokument - seriál
    Acta Universitatis Carolinae. Geologica
    Vol. 41, no. 1
    p. 113-125
    5 obr., 1 tab., 2 s.bibl.
    Zkr. název ser.: Acta Univ. Carol., Geol.
Předmětová skupina
    chemismus hornin
    krušnohorské krystalinikum
    metamorfóza vysokotlaká
    podmínky P-T
    vrásnění variské
Geografické jméno
Klíčové slovo
Abstrakt (anglicky)
   Ga-ky granulites occur in the domains of different sizes within granulite bodies (Blanský les, Prachatice, Křišťanov, etc.) that arc parts of Moldanubian and Saxothuringian nappes. Ga-ky granulites have granoblastic textures and show high P/T equilibria (T=750-950°C, P=10-15 kb). Major elements composition of granulites is characterized by eutectic Ab-Or-Qz relations with rather high Qz contents and peraluminous nature. The trace elements abundances have granite features: high LIL contents, LREE enriched patterns, negative Eu anomaly, but low Th and U and varied Zr abundance. The contents of siderophile and transitional elements are slightly higher than corresponding contents of granites. Positive correlation of Zr with Th and U, and negative correlation of Zr with elements c.g., Rb suggests that melting or removal of zircon played major role in granulite trace element signature.
   Granulite bodies contain blocks and xenoliths of ultramafic rocks not related to metamorphic structures of granulites. Xenoliths occur in both ga-ky (unretrogressed) and ga-bi (retrogressed) rocks. Ultramafic rocks were incorporated into granulites in the solid state and their mineral equilibrium indicate origin in the mantle and consequent fast exhumation. The interval of time of protolith crystallization (i.c., 370-340 Ma) is narrow and indicates "granulite event" in the early Variscan. The event is contemporaneous with the emplacement of other "igneous rocks" that share granulite facies features (e.g., opx-cpx parageneses), have strong geochemical mantle signatures and are considered to be part of major batholiths (durbachite types) in Moldanubian terrain (Tábor, Jihlava, Weinberg, Rastenberg).
   Differences in metamorphic grade of granulites and surrounding gneisses the composition, and the presence of ultramafic xenoliths indicate that ga-ky granulites are pristine dehydration melts that may have formed at collision environment at the expense of crustal material of lower plate
    Česká geologická služba
Kód přispěvatele
    ČGS (UNM)
Zdrojový formát
Datum vložení
    14. 1. 2008
Datum importu
    8. 8. 2012