Podrobnosti záznamu

Název
    Intracrystal microtextures in alkali feldspars from fluid deficient felsic granulites: A chemical and TEM study
Autor
    Abart, Rainer
    Habler, Gerlinde
    Rhede, Dieter
    Tajčmanová, Lucie
    Wirth, Richard
Jazyk
    anglicky
Typ dokumentu
    článek v periodiku
Zdrojový dokument - seriál
    Contributions to Mineralogy and Petrology
Svazek/č.
    Roč. 164, č. 4
Strany
    15
Rok
    2012
Výraz tezauru
    feldspars, perthite, spinodal decomposition, nucleation, granulites, TEM
Klíčové slovo
    Alkali
    Chemical
    Deficient
    Feldspars
    Felsic
    Fluid
    Granulites
    Intracrystal
    Microtextures
    Study
Abstrakt (anglicky)
   Samples of essentially "dry" high-pressure felsic granulites from the Bohemian Massif (Variscan belt of Central Europe) contain up to 2 mm large perthitic alkali feldspars with several generations of plagioclase precipitates in an orthoclase-rich host. The first generation takes the form of lenses homogeneous in size whereas the size of a second generation of very thin albite-rich precipitates is more variable with comparatively high aspect ratios. In the vicinity of large kyanite, garnet or quartz inclusions, the first generation of plagioclase precipitates is significantly less abundant, the microstructure is coarser than in the remainder of the perthitic grain, and the host is a tweed orthoclase. The first generation of precipitates formed at around 850°C during the high pressure stage (16-18 kbar) of metamorphism. Primary exsolution was followed by primary coarsening of the plagioclase precipitates which still took place at high-temperatures (850-700 °C). The coarsening was pronou
   nced due to the access of fluids in the outer portions of the perthitic alkali feldspar and in more internal regions around large inclusions. The second generation of albite-rich precipitates was formed at around 570 °C. TEM investigations revealed that the interfaces between the second generation plagioclase lamellae and the orthoclase-rich host are coherent or semi coherent. During late evolutionary stages of the perthite, albite linings were formed at phase boundaries and the perthitic microstructure was partially replaced by irregularly shaped precipitates of pure albite with incoherent interfaces. The albitization occurred below 400°C and was linked to fluid infiltration in the course of deuteric alteration. Based on size distribution analysis, it is inferred that the precipitates of the first generation were most probably formed by spinodal decomposition whereas the precipitates of the second generation rather were formed by nucleation and growth.
Přispěvatel
    Česká geologická služba
Kód přispěvatele
    ČGS (RIV)
Zdrojový formát
    R
Datum importu
    15. 10. 2014