Timing and kinematics of the Variscan orogenic cycle at the Moldanubian periphery of the central Bohemian Massif

Abstract

The high-grade metamorphic complexes along the northern Moldanubian periphery of the central Bohemian Massif provide an outstanding structural record of all episodes of the collisional evolution of the Variscan Orogeny. The kinematics and timing of the orogenic processes were examined by structural and microstructural studies of middle and lower crustal rocks combined with xenotime and monazite geochronology. Four distinct tectonic events were identified. A first relict sub-horizontal fabric S1 associated with high-pressure–high-temperature metamorphism was only developed in the lower crustal rocks and was related to back-arc extension or lower crustal flow in a supra-subduction domain. This fabric was completely reworked to the subvertical foliation S2 at c. 340 Ma by major collisional thickening, leading to juxtaposition of the lower and middle crust. Thereafter, extensional collapse of the thickened orogenic system caused strong refolding to the high-temperature sub-horizontal fabric at c. 325 Ma. The region was subsequently affected by NNE–SSW-oriented horizontal shortening related to dextral shearing and the clockwise rotation of crustal blocks adjacent to the large-scale dextral shear zone (the Elbe Zone). This led to fragmentation and reorientation of the Moldanubian margin to its current position. Supplementary material: A summary of the main microstructural features related to the defined deformation phases, the results of the U–Pb laser ablation inductively coupled plasma mass spectrometry analyses of xenotime and monazite, back-scattered electron images and rare earth element compositional maps are available at https://doi.org/10.6084/m9.figshare.c.5708800.v1