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

Abstract

The deformation behavior of calcite has been of longstanding interest. Through experiments on single crystals, deformation mechanisms were established such as mechanical twinning on \({\mathbf{e}} = \{ \ifmmode\expandafter\bar\else\expandafter\=\fi{1}018\} {\left\langle {40\ifmmode\expandafter\bar\else\expandafter\=\fi{4}1} \right\rangle }\) in the positive sense and slip on \({\mathbf{r}} = \{ 10\ifmmode\expandafter\bar\else\expandafter\=\fi{1}4\} {\left\langle {20\ifmmode\expandafter\bar\else\expandafter\=\fi{2}\ifmmode\expandafter\bar\else\expandafter\=\fi{1}} \right\rangle }\) and \({\mathbf{f}} = \{ \ifmmode\expandafter\bar\else\expandafter\=\fi{1}012\} {\left\langle {0\ifmmode\expandafter\bar\else\expandafter\=\fi{2}2\ifmmode\expandafter\bar\else\expandafter\=\fi{1}} \right\rangle },\) both in the negative sense. More recently it was observed that at higher temperatures \({\mathbf{f}}\{ \ifmmode\expandafter\bar\else\expandafter\=\fi{1}012\} {\left\langle {10\ifmmode\expandafter\bar\else\expandafter\=\fi{1}1} \right\rangle }\) slip in both senses becomes active and, based on slip line analysis, it was suggested that \({\mathbf{c}}(0001){\left\langle {11\ifmmode\expandafter\bar\else\expandafter\=\fi{2}0} \right\rangle }\) 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 \((0001){\left\langle {11\ifmmode\expandafter\bar\else\expandafter\=\fi{2}0} \right\rangle }\) 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.