Basal slip and texture development in calcite: new results from torsion experiments

The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation mechanisms were established such as mechanical twinning on e = {(1) over bar 018} [40 (1) over bar1] in the positive sense and slip on r = {10 (1) over bar4} [20 (2) over bar(1) over bar] and f {(1) over bar 012} [0 (2) over bar2 (1) over bar] both in the negative sense. More recently it was observed that at higher temperatures f{(1) over bar 012} [10 (1) over bar1] slip in both senses becomes active and, based on slip line analysis, it was suggested that c(0001) [11 (2) over bar0] slip may occur. So far there had been no direct evidence for basal slip, which is the dominant system in dolomite. With new torsion experiments on calcite single crystals at 900 K and transmission electron microscopy, this study identifies (0001) [11 (2) over bar0] slip unambiguously by direct imaging of dislocations and diffraction contrast analysis. Including this slip system in polycrystal plasticity simulations, enigmatic texture patterns observed in compression and torsion of calcite rocks at high temperature can now be explained, resolving a long-standing puzzle.