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Zircons in Variscan granites from the Slavonian Mountains, Croatia

The Slavonian Mountains in Croatia expose Variscan crystalline basement of the Tisia terrane. Apart from different metamorphic units, this basement comprises large bodies of Variscan granites. In the course of current attempts to constrain the formation ages of these granitic rocks by means of LA-SF-ICP-MS-based U-Pb zircon dating, a detailed study of the accessory zircon crystals was undertaken with reference to morphology, internal growth textures and crystal chemistry. Eight samples of granites from Papuk and two granite samples from Psunj were prepared for the study. The work was carried out using a combination of methods, including optical microscopy, cathodoluminescence (CL) and backscattered-electron imaging (BSE), electron microprobe and laser ICP-MS analysis. The granite samples from Psunj carry a distinctive zircon population characterized by relatively large, stubby to normal prismatic zircons with prominent {; ; 100}; ; and {; ; 101}; ; crystal faces. {; ; 211}; ; and {; ; 110}; ; faces are small or missing, as is often the case in high-temperature I-type and A-type granites [2]. Characteristic are numerous inclusions of tiny apatite needles and uranium rich inner zones, which are sometimes metamict. Zircons in the Papuk granites are short prismatic to normal prismatic, with prominent steep pyramids {; ; 211}; ; and a dominance of the {; ; 110}; ; prism. Short prismatic crystals often contain a large inherited core with bright CL signal, mantled by an oscillatory zoned outer growth shell. Zircon types are consistent with the interpretation of, according to which the granites from Papuk have an S-type origin.

zircon; Variscan; granite; Papuk; Psunj; Slavonian Mountains

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