VARISCAN DEFORMATION, MICROSTRUCTURAL ZONATION AND EXTENSIONAL EXHUMATION OF THE MORAVIAN CADOMIAN BASEMENT

The Cadomian Dyje Batholith, in the foot-wall of the Variscan Moravian nappe pile, has been involved in Variscan ductile deformation. The Ca domian Brunovistulian rocks were obliquely underthrusted during Carbon iferous dextral transpression. Strain intensity is inversely proportio nal to the distance from the contact of the Variscan thrust front. The microstructures of deformed granodiorites and quartz-diorites show a characteristic zonality marked by relatively high temperature flow in the west (550-580 degrees C) characterized by dynamic recrystallizatio n of feldspars and grain boundary migration recrystallization of quart z. The size of quartz grains decreases with decreasing strain towards the east. At the easternmost part of the autochthonous Dyje massif, fr acturing of feldspar and subgrain rotation recrystallization of quartz predominate. Flow stress estimates calculated from recrystallized qua rtz grain size show a regional increase of stress intensity from the h ighly strained margin towards the less deformed core of the Dyje massi f. This microstructural zonation is oblique with respect to the major thrust boundary and corresponds roughly to metamorphic isogrades. The microstructural zonation reflects underthrusting of the Brunovistulian domain below the Moldanubian nappe. The main ductile tectonic event D I is followed by a retrogressive brittle-ductile and brittle deformati on D-2. D-2 results in the development of shear zones and faults super imposed on the D-1 mylonite fabric. D-2 is related to extension obliqu e to the D-1 fabric, associated with detachment and the westward movem ent of the Moravian nappes. (C) Elsevier, Paris.