Petrostrukturni vztahy mezi granitoidy v oblasti Nove Pece (moldanubikum, Sumava)

Petrological and structural evolution of granitic rocks in the area was studied in connection with geological mapping of the map sheet Nová Pec 32-142. Durbachites (amphibole-biotite melasyenite) show variation in the quantitative mineralogical composition. The phenocrysts of K-feldspar carry Bt and Pl inclusions. Plagioclase composition varies from An63 to An10, biotite is compositionally homogeneous. Some amphibole (actinolite) crystals contain relics of diopside and actinolite with increased Mg content. Fine-grained biotite granitoids are characterised by rather uniform plagioclase composition (An30-An1). Biotite shows variation in Mg, Fe 2+ and AlIV proportions. Minor garnet contains Alm > 70 mol. %. Three deformation phases, corresponding to metamorphic foliations S1, S2 and S3 have been recognised in granulitic gneisses. The foliation S2 (with some relicts of S1) steeply dipping from the NE to SE is refoliated in some domains by subhorizontal foliation S3 dipping to the NNW. Fine-grained granitoids show a subsolidus deformation of variable intensity. Planar structures dip under a low angle to the NW and become indistinct towards the W. Durbachites show a strong magmatic foliation: (i) relict - subvertical, (ii) penetrative - subhorizontal with a shallow dip to the NW. Subsolidus deformation in durbachites occurs in marginal parts of the intrusions. Granite of the Plechý massif shows a weak magmatic foliation, which is discordant in relation to the regional structures. Recrystallized granulites represent the oldest unit of the area. Their superimposed deformation (D2, D3) and retrogression coincided with a polyphase emplacement of durbachites (and formation of their internal magmatic structures) and emplacement of fine-grained granitoids. The intrusion of the Plechý granite massif took place post-tectonically in relation to the deformation history of the area.