Microstructures in hornblende of a mylonitic amphibolite

Abstract: The microstructure in a dynamically recrystallized amphibolite ofa deep crustal shear zone from the Ivrea Zone, NW Italy, has been i vestigated byconventional and high resolution transmission electron microscopy. The microstructure in the amphibole phase consists of recrystallized grains, subgrains, free dislocations and various stacking faults bounded by partiaI dislocations. The Burgers vectors of the dislocations are [001], [100], 1/2 <110> and very likely <101>. Dislocations with [100] Burgers vector and [001] line direction are mainly arranged in low angle tilt boundaries lying parallel to (100) planes. Faceting of these subgrain boundaries i produced by 1/2 <110> edge dislocations dissociated on (010). The free dislocations are mainly non-dissociated [001] and[100] dislocations gliding on (100) and (010) planes, respectively. It is assumed that [001] and [100] dislocations recombined to form <101> dislocations which subsequently dissociate in (010). The stacking faults extended on (010) planes either have pyroxene or sheet silicate character. They act as obstacles for dislocation motion on the main slip system (100)[001]. High resolution imaging of the dislocation cores suggests hese areas consist of lower density material providing channelways for ast diffusion which may be responsibl