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50 P. HASALOVÁ ET AL.creep <strong>and</strong> grain boundary sliding deformation mechanisms.The types II–IV microstructures developed bygranular flow accompanied by melt-enhanced diffusion<strong>and</strong>/or melt flow. However, the amount <strong>of</strong> melt presentnever exceeded a critical threshold during the deformationto allow free rotation <strong>of</strong> biotite grains.The model <strong>of</strong> melt infiltration based on <strong>structural</strong><strong>and</strong> micro<strong>structural</strong> observation is supported by thermodynamic(Hasalova´ et al., 2008a) <strong>and</strong> geochemical<strong>modelling</strong> (Hasalova´ et al., 2008b). Although our dataseem to be consistent with such a model, there are stilla number <strong>of</strong> issues to be resolved (e.g. time-scale <strong>of</strong> theprocess, the character <strong>of</strong> the melt <strong>and</strong> the grain-scaledeformation mechanisms enabling pervasive flow <strong>of</strong>viscous melt). Nevertheless, our model has pr<strong>of</strong>oundconsequences for the petrogenesis <strong>of</strong> migmatites, therheology <strong>of</strong> anatectic regions during syn-orogenicexhumation <strong>and</strong> melt transport in the crust.ACKNOWLEDGEMENTSThis work was financially supported by the GrantAgency <strong>of</strong> the Czech Academy <strong>of</strong> Science (Grants No.IAA311140 <strong>and</strong> No. 205/04/2065) by an internalCNRS funding (CGS/EOST) <strong>and</strong> by the FrenchNational Agency (No. 06-1148784). Visits by P.Hasalova´ to ULP Strasbourg were funded by theFrench Government Foundation (BGF). We gratefullyacknowledge A. Langrova´ from the Institute <strong>of</strong>Geology at the Czech Academy <strong>of</strong> Sciences for operatingthe microprobe. We also thank the reviewersC. Rosenberg, R. Weinberg <strong>and</strong> H. Stu¨ nitz for theirconstructive comments <strong>and</strong> suggestions for improvingthis paper, <strong>and</strong> the Journal editor M. Brown for hiscareful h<strong>and</strong>ling <strong>of</strong> the manuscript. R. Powell <strong>and</strong>M. Brown are thanked for helpful discussions.REFERENCESAdams, B. L., Wright, S. I. & Kunze, K., 1993. Orientationimaging: the emergence <strong>of</strong> a new microscopy. MetallurgicalTransactions A, 24, 819–831.Arbaret, L., Fern<strong>and</strong>ez, A., Jezˇek, J., Ildefonse, B., Launeau, P.& Diot, H., 2000. 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