HIGH-TEMPERATURE DEFORMATION OF A GRANITOID FROM THE ZONE OF ERBENDORF-VOHENSTRAUSS (ZEV)

Microfabrics and textures indicate that progressive mylonitization of granitoids from the vicinity of the KTB site occurred under high tempe rature and probably prograde conditions by pure shear deformation. Dif fusion-controlled deformation mechanisms and diffusional mass transfer for all rock-forming minerals were prominent processes which also con tributed to the development of compositional layering. Typical chessbo ard patterns in quartz suggest that even the latest increments of plas tic deformation took place at high temperatures within the stability f ield of high quartz. Largely constant chemical bulk-rock compositions and lack of retrogressive reactions are evidence of a dry and closed s ystem during mylonitization. Only a late post-mylonitic fluid influx i s documented by secondary fluid inclusions along healed microcracks. T aking recent geochronological data into account, different geological scenarios are most suitable: (a) intrusion of the protolith between 52 5 and 475 Ma into Cadomian basement and subsequent mylonitization in a related extensional regime; and (b) Early Variscan mylonitization in a subduction zone environment between 475 and 380 Ma.