High-temperature deformation of calcite single crystals by r⁺ and f⁺ slip

Optical quality calcite single crystals have been uniaxially compressed at constant strain rates and temperatures (T) in the range 3 × 10 ^-4 to 3 × 10 ^-7 s ^-1 and 550-800°C respectively. The tests were performed with the compression direction parallel to [4041], i.e. parallel to the intersection of two cleavage rhombs. At strains above 1% strain, steady state flow was observed at T ≥ 600°C. The flow stresses at these temperatures were found to be rather insensitive to strain rate, and can be empirically described by a power law creep equation with a stress exponent ranging from c. 13 at 600°C to c. 9.5 at 700-800°C. The active glide systems were identified by slip line analysis. The crystals were found to deform by e-twinning at T < 600°C, and by slip on a single r<2021> system plus a single f system in the so-called positive sense at T < 600°C. The effective slip direction on the active f-plane was of <1011> type rather than the <0221> type reported previously. The observed creep behaviour in the slip dominated regime has been compared with microphyical models. The deformation behaviour seems best explained by cross slip or glide-controlled creep models, or a combination of these.