Critical re-evaluation of differential stress estimates from calcite twins in coarse-grained limestone

Abstract

Comparison of two techniques to estimate differential stress magnitude based on calcite twinning reveals significantly different calculated values of differential stress for limestone experimentally and naturally deformed at low temperature. This inequality may be due to fundamental differences between the rock type (marble versus limestone) and deformation temperatures (above and below 200°C) for samples used in technique calibration versus samples used in testing and application. A technique that was empirically derived from marble experimentally deformed at 200–800°C yields values of differential stress that are factors of 2 to 9 times larger than maximum differential stress measured during experimental deformation of limestone at low temperature (<200°C). Differential stress estimates from naturally deformed rocks differ by factors of 4 to 20, depending on the stress estimation technique used. Calcite tends to develop thin twins when deformed at temperatures below 200°C, and thick twins when deformed at temperatures above 200°C. Because of the temperature dependence of calcite-twin morphology, and possible effects of strain, grain size, and porosity, twin-based differential stress estimates should be used cautiously and particular attention given to deformation temperature.