Dyke swarm of highly evolved felsitic alkali-feldspar granite porphyry near Milevsko, Central Bohemian Pluton


Authors: Vrána S

Published in: Bulletin of Geosciences, volume 74, issue 1; pages: 67 - 74;

Keywords: felsitic granite porphyry, highly differentiated rocks, Central Bohemian Pluton,

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Dyke swarm of late-Variscan felsitic alkali-feldspar granite porphyry around Milevsko, south-central Bohemia, is associated with the Milevsko circular structure (D= 8 and 4.5 km) expressed in surface morphology. Micro-spherulitic and granoblastic structures indicate devitrification of originally glassy rocks. The felsitic porphyries belong to some of the chemically most evolved rocks in the Bohemian Massif. Non-chondritic Zr/Hf and Y/Ho ratios suggest that the rocks solidified from a transitional melt/aquaeous fluid system or from melts highly charched with fluids. The Milevsko dyke swarm and its structural setting is similar to the Pelhrimov dyke swarm and structure (D=9.6 km) located 60 km to the east and interpreted as erosional section of an explosive volcano-tectonic structure.