Quantitative structural analyses and numerical modelling of ...

126 J. FRANĚK ET AL.development of the irregular to amoeboid domains(e.g. Fig. 9a,b) of fine-grained regularly distributedK-feldspar and plagioclase matrix.Lower crustal ascent and strength evolution of felsicgranulitesThe onset of the D2 deformation is marked by highlynon-cylindrical folding of the S1 anisotropy prior tothe S2 cleavage development (Figs 4a,b & 16, blockdiagram 3). The formation of a typical Variscan felsicgranulite fine-grained microstructure with highlyelongated quartz ribbons is the main result of the D2deformation (Figs 5e & 9e) that is contemporaneouswith the development of the granular Type I microstructure.Petrological modelling and mineral zoning,particularly the decrease of the grossular componentin garnet, suggest that between the perthite growthand the end of the D2 there was significant decompressionof 0.8 GPa at slightly decreasing temperatureover a time span of several million years (Figs 8& 16). That means the S2 microstructure developedat slightly lower temperature compared with the S1and under continuously decreasing pressure as indicatedby a number of decompression microstructuressuch as plagioclase rims around kyanite and garnet(Figs 5e & 6h). This conclusion agrees with theobservations of spinel–plagioclase and garnet coronasdeveloped around kyanite, which form characteristicdecompression microstructures in S2 (Sˇtípska´ et al.,2010). The common denominator of these coronas isthat they are elongated parallel to S2 foliation(Fig. 6h) and therefore developed at the end of theD2 deformation.The small interstitial quartz grains, discontinuousalbite films at plagioclase or K-feldspar boundariesand cuspate feldspar grain shapes (Fig. 9d) are consistentwith the presence of syn-deformational intergranularpartial melt in the granulitic S2 matrix, aconclusion previously suggested by Franeˇk et al.(2006) and supported also by dykes of felsic granulitecrosscutting mafic boudins embedded in S2. Tajčmanova´et al. (2006, 2007) inferred a low content ofpartial melt (