| Abstract: | Naturally deformed clinoamphiboles from the Selbu-Tydal and Forsbäck-Tärnaby areas of the Scandinavian Caledonides exhibit a well defined subgrain microstructure. From a transmission electron microscopy study (TEM), the subgrain boundaries are shown to consist of arrays of positive and negative screw dislocations with Burgers vector
. Locally expanded loops are present having long screw segments. The subgrain boundaries are parallel to rational crystallographic planes of the type (hk0). The density of isolated dislocations within the subgrains is low. In addition planar defect structures parallel to (010) and bounded by screw dislocations with
are observed. Based on metamorphic criteria the P−T values at the time of the amphibole growth have been estimated at 450°–600°C and 4–6 kbar, and these represent maximum conditions for the deformation. The present results indicate that slip on (hk0) 001] is an operative deformation mechanism in naturally deformed clinoamphiboles. |
