Slip systems in calcite single crystals deformed at 300–800°C

Abstract

In an attempt to resolve questions recently raised regarding the principal high‐temperature slip systems in calcite, optical quality single crystals have been uniaxially compressed at 300–800°C and at a constant strain rate of ∼ 3×10−5 s−1. In addition, a single strain rate cycling test was performed at 650°C. The tests were all carried out with the compression direction parallel to , which lies at ∼30° to the c axis and makes angles of 52° and 23° with the poles to two rhombohedral (r) planes. Axial strains of 5–16% were achieved in the tests. The stress‐strain curves obtained showed three‐stage hardening behavior, while the strain rate cycling data showed flow stresses to be rather insensitive to strain rate with empirical power law fits yielding a conventional stress exponent of 22–30 at strains ≥ 5%. The active glide systems were identified by slip line analysis. Slip on r in the so‐called negative sense was found to be an important deformation mechanism across the entire range of temperatures investigated, while slip on a single f system in the negative sense became important at 650°C and above. The active f slip direction was of type, confirming the existence of a new set of f slip systems, namely, f , as opposed to the generally accepted f systems. In addition, clear evidence was found for significant slip on the basal (c) plane at temperatures above 600°C, probably in the 〈a〉 direction. By comparison with earlier data on crystals from the same batch, no evidence was found for significant strength asymmetry on the r and f slip systems in the positive and negative senses. Notably, the presently observed f and c sup systems have not been taken into account in previous modelling studies of plasticity and texture (i.e., crystallographic preferred orientation) development in calcite rocks, and r slip is usually taken as stronger in the positive than negative sense. Our results therefore imply a need for renewed modelling work on calcite, particularly regarding texture development at relatively high temperatures.