Granulites, partial melting and the rheology of the lower crust

This Special Issue of the Journal of Metamorphic Geology comprises seven invited papers from the Granulites and Granulites 2009 conference held in Hrubá Skála Chateau, Czech Republic, during the period 13–15 July 2009, and convened by Karel Schulmann (University of Strasbourg), Michael Brown (University of Maryland), Richard White (University of Mainz), Ondrej Lexa (Charles University, Prague) and Patrick O Brien (University of Potsdam). The purpose of the conference was to review and discuss recent advances in understanding crustal processes at P–T conditions characteristic of the granulite facies, including high-pressure and ultra high temperature granulites, with particular reference to the rheology of the crust and orogenic processes at these conditions. The conference was preceded by a 3-day short course on modelling of deformation microstructures using the Elle software and on the quantification of metamorphic microstructures using the Poly Lx software. The short course was given by Paul Bons from the University of Tübingen and Ondrej Lexa from Charles University, Prague during the period 9–12 July 2009. The short course was followed by a 3-day field excursion to examine granulites of the Saxony granulite massif, the Erzgebirge and the Egger complex, and to visit the South Bohemian granulite massifs, with a special focus on the Blansky Les granulite – the largest felsic granulite massif in Europe. The pre-conference field excursion was led by Patrick O Brien from the University of Potsdam, Jiri Konopasek, Jan Franek and Vojtech Janousek from the Czech Geological Survey, and Karel Schulmann from the University of Strasbourg. The conference was followed by a 3-day field excursion to the Austrian St. Leonhard granulite massif and the Drosendorf window, and the Gföhl unit and the associated Varied and Monotonous group rocks, at the eastern margin of the Bohemian massif, where structures related to channel flow and extrusion of orogenic lower crust at the head of the channel were examined. Ondrej Lexa and Martin Racek from Charles University, Prague, and Karel Schulmann from the University of Strasbourg led this postconference excursion. Following the second field excursion, Roger Powell from the University of Melbourne, Tim Holland from the University of Cambridge and Richard White from the University of Mainz led a short course on Calculating Metamorphic Mineral Equilibria held at Charles University, Prague, during the period 20–23 July 2009. The papers in this Special Issue exemplify the multidisciplinary nature of the study of granulites. The first four papers concern the mechanical behaviour of convergent continental margins, with a particular emphasis on the rheological role of granulites and partially molten crust in the evolution of collisional orogens and on the mechanisms of exhumation of orogenic lower crust. The last three papers concern new advances in the petrological study of granulites, specifically the development of the characteristic microstructure of felsic granulites of the eastern sector of the European Variscides, the development of postpeak mineral assemblages in microstructures such as coronae and symplectic intergrowths, and the calculation of phase diagrams to investigate the growth and dissolution of zircon in relation to the evolution of rock-forming mineral assemblages.