Podrobnosti záznamu

    Accessory titanite: an important carrier of zirconium in lamprophyres
Údaj o odpovědnosti
    Wolfgang Seifert, Wolfgang Kramer
    Kramer, Wolfgang
    Seifert, Wolfgang
Zdrojový dokument - seriál
    Vol. 71, no. 1
    p. 81-98
    4 obr., 3 tab., 2 s. bibl.
    Zkr. název ser.: Lithos
Předmětová skupina
    chemismus minerálů
    kenozoické vulkanity Českého masivu
    mísení magmat
    zonálnost krystalu
Geografické jméno
    Chlum (Česká Lípa)
    Leština (Ústí nad Labem)
    Tachovský vrch (Česká Lípa)
    Valkeřice (Děčín)
Klíčové slovo
Abstrakt (anglicky)
   he chemical composition of minerals from a suite of Variscan lamprophyres (kersantite, minette, spessartite and vogesite) from the Saxothuringian Zone of the Variscan orogen, Germany, were investigated by electron microprobe. These lamprophyres usually contain small grains (<50 'mikro'm) of Zr-bearing titanite as the only primary mineral containing traceable zirconium. A latestage residual alkaline melt within the lamprophyric magma is considered to have crystallized the Zr-rich titanite. The titanite typically has euhedral Zr-rich cores, mantled by Zr-poor overgrowths. This compositional change is explained by rapid decrease of temperature during magma uprise and emplacement. Relatively high Zr contents and compositional and textural heterogeneities (e.g. syenitic schlieren, veins and globules) within the lamprophyric host rocks are evidence of magma mixing.
   Incorporation of Zr into titanite apparently takes place as a coupled substitution (Ti4 + + Al3 +<=Zr4 + + Fe3 +) rather than as a simple 1:1 replacement of Ti by Zr. A ZrO2 content of about 6 wt.per cent (equivalent to "proportionall" 0.10 atoms per formula unit Zr) is implied as the upper concentration limit in titanite. Locally occurring higher values are attributed to tiny inclusions of secondary Zr phases. In carbonate-rich portions of lamprophyres, titanite is transformed into an unindentified TiO2 phase. High-(Al,F) titanite (XA1 up to 0.54), restricted in occurrence to the contact between tonalite porphyry and kersantite, formed under the conditions of high fluorine activity connected with the rhyolitic magmatism. The results show that the Zr budget of lamprophyres, and possibly of other mafic igneous rocks lacking zircon, is strongly governed by titanite.
   Element distribution patterns in titanite are a key to the better understanding of magmatic evolution and petrogenesis of lamprophyres
    Česká geologická služba
Kód přispěvatele
    ČGS (UNM)
Zdrojový formát
Datum vložení
    5. 2. 2009
Datum importu
    8. 8. 2012