"Evolution of flow, architecture and rheology of an orogenic accretionary wedge (Orlica Snieznik Dome - Sudete)"

Evolution of flow, framework and rheology of an orogenic accretionnary prism is assessed with a multi-method geological investigation. The Orlica-Śnieżnik Dome in the Sudetes is situated in front of a rigid indenter. Its structure is explained by an influx of felsic continental crust from the subducted passive margin until 50-60 km depth in a crustal scale accretionnary wedge. The incipient root is composed of lower crustal felsic material partially melted with smaller pieces of basic rocks. Structurally above it lies an intermediate level of weakly deformed augen orthogneiss and metasediments of the middle crust. This rheologicaly heterogeneous layered infrastructure due to burial flow is subsequently reworked in front of the rigid buttress, developing major two-scale wave-length crustal upright folds. It permits vertical material transfers between different crustal levels throughout the infrastructure that is responsible for the growing dome. It is achieved by the detachment of the suprastructure and localized ductile thinning on the top of the exhumed infrastructure. Topography is adjusted by infill of adjacent syn-orogenic basins. This study highlights the shared evolution of the different crustal levels, in particular during influx and burial along the subducting plate. Here, the deformation in orthogneisses bearing eclogites is very localized and allows to passively transport large pieces of weakly deformed orthogneiss into the apex of the corner. This localization is explained by a switch in the mode of recrystallisation from dislocation creep to grain boundary sliding diffusion creep which is chemically enhanced by high nucleation of interstitial phases in monomineralic aggregates. This evolution that appears in a prograde gradient until eclogitic facies in mylonitic orthogneisses leads to drastic reaction weakening and strain localization. This switch in mode of deformation is also observed in the anticline cored by migmatites in front of the butress during exhumation. It permits the weakening of the rocks that is necessary to explain flow in the whole felsic corner.