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519929 
Journal Article 
Typology, chemistry and origin of zircon from alkali basalts of SE Saxony (Germany) 
Seifert, W; Rhede, D; Tietz, O 
2008 
1 
Neues Jahrbuch fuer Mineralogie. Abhandlungen
ISSN: 0077-7757 
E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG 
STUTTGART 
184 
3 
299-313 
English 
WOS:000254777700006 
To clarify the origin of zircon from Tertiary alkali basalts from SE Saxony (Germany), electron-microprobe analysis was combined with detailed studies of crystal morphology and inclusion types. Morphological and chemical typology of representative crystals from the Seufzergrundel placer (Elbe zone) essentially distinguish two zircon types crystallized in an alkaline environment: (I) a mostly drop-like, rounded, honey-coloured, gem-quality zircon relatively poor in trace elements, and a (II) mostly nontransparent, red brown to grey zircon rich in trace elements and with chaotic zoning pattern. A further zircon type, rich in trace elements and distinctly zoned is assumed to be of calc-alkaline granite origin. Inclusions of SO3-rich apatite and magnesiokatophoritic amphibole in zircon indicate an alkaline, probably syenitic or nepheline-syenitic source for the two main types of zircon. Thorite and uraninite included in zircon are interpreted as exsolutions from metastable zircon-thorite solid solutions. Chemical Th-U-total Pb age determinations of these exsolutions by electron microprobe interpreted as "exsolution age" confirm a Tertiary age (16 8 to 39 +/- 4 Ma). The "Ti-in-zircon" thermometry results in = 800 +/- 50 degrees C for zircon from an alkaline source. In comparison with the zircon from the Seufzergrundel placer, first analytical results of zircon from basalt- and phonolite-related occurrences of the Upper Lusatia (Oberlausitz) show similar features, but a greater variability in minor and trace element contents. We argue that the majority of zircon studied is genetically connected with the Tertiary, rift-related, alkaline magmatism, the centre of which is the Eger (Ohre) Graben in North Bohemia. 
zircon; typology; mineral chemistry; inclusion; geothermometry; chemical age determination; alkali basalt; Tertiary; Saxony; trace-element composition; upper-mantle; igneous zircon; megacrysts; age; cathodoluminescence; microprobe; minerals; province; genesis