DETERMINING DEVIATORIC STRESS TENSORS FROM CALCITE TWINS - APPLICATIONS TO MONOPHASED SYNTHETIC AND NATURAL POLYCRYSTALS

Theoretically, calcite twins analysis makes possible the full determination of the deviatoric stress tensor responsible for the formation of the twin lamellae, that is, the orientations of the principal stress axes and the three differential stress values (σi–σj) may be calculated, assuming conditions of constant resolved shear stress for twinning. Inverse method using nonlinear regression and robust estimation is proposed. Applications to monophased synthetic polycrystals that are generated numerically by solving the direct problem and to a natural sample from the Quercy (southwest of France) have given good results. Comparison with the first method proposed by Turner (1953), modified by Nissen (1964) for principal stress orientations and by Jamison and Spang (1976) for differential stress values, clearly emphasizes the considerable interest of this new method. Copyright 1990 by the American Geophysical Union.