Pages: 151 - 160
Abstract: The Homolka granite stock (southern Bohemia, Czech Republic) is a highly evolved topaz-bearing and phosphorus-rich intrusion penetrating the Lasenice and Cimer S-type granites of the late-Variscan South-Bohemiam (Moldanubian) pluton, subvolcanic dykes of microgranite to granite porphyries are also widespread. Study of accessory zircon revealed an extensive amount of old inherited zircon in the Homolka granites. On the basis of back-scattered electron images and microprobe study, the inherited zircon of the Homolka Granite is identical to the zircon from the Lasenice and Cimer granites. This older zircon forms transparent crystals with oscillatory zoning and low Hf, Y, U and P contents. Younger zircon of the highly evolved Homolka Granite exhibits transparent crystals with oscillatory to irregular zoning and metamict grains with high Hf (up to 12.3 wt. % HfO2), often also Y, U and P. If 30 to 50 vol. % of zircon is estimated to be inherited, the calculation of zircon saturation temperature gives TS = 720–760 °C for the Cimer and 640–680 °C for the Lasenice zircon, and 610–650 °C for the Homolka zircon. The subvolcanic microgranite-porphyry dyke gave TS = 690–730 °C. These zircon data indicate that the Homolka Granite is a product of advanced fractional crystallization from a magmatic source similar to the Cimer Member of the Eisgarn Suite.
Keywords: Czech Republic, South-Bohemian (Moldanubian) pluton, Homolka Granite, zircon saturation temperature, electron microprobe, BSE, zircon typology, zirconDownload PDF document Show Text Version