Structural evolution of the central part of the Krušné hory (Erzgebirge) Mountains in the Czech Republic—evidence for changing stress regime during Variscan compression

In the central part of the Krušné hory (Erzgebirge) Mountains, the parautochthonous metasedimentary basement has been overthrust by a crustal nappe of fine- and coarse-grained orthogneisses. The thrust boundary is defined by the presence of mafic eclogites with preserved subduction-related fabric. Westward thrusting of an allochthonous unit is associated with the development of the main metamorphic foliation and lineation in non-eclogitic lithologies. Buttressing of the allochthonous body from the west is responsible for the development of late, large-scale folds with N–S trending hinges and vertical axial planes. Subsequent N–S compression leads to large-scale folding of both the parautochthonous and allochthonous units. This deformation produces km-scale antiforms with hinges plunging to the west and is associated with the development of the E–W stretching lineation as a result of complete reworking of earlier fabric in the limb zones. N–S shortening is also associated with the development of small-scale folds and brittle-ductile kink bands suggesting a decrease in temperature, and, thus, uplift of the whole studied area during this event. The last stage of deformation is characterised by the development of kink-band folds and a crenulation cleavage. These structures suggest a sub-vertical direction of principal compression, developed exclusively in those parts of the area in which the N–S compression produced steep planar fabric.