The texture presented in Fig. 2a favours tensile 10-12 twinning during compression along R3 axis (Z axis of the sample). That is because c axes of crystallites lie perpendicular to axis of compression and they are subjected to tension in this deformation mode.
Due to presence of six equivalent {10-12} planes in a hexagonal crystal lattice, grain can undergo twinning in six different ways: {10-12}<-1011>, {01-12}<0-111>, {-1102}<1-101>, {-1012}<10-11>, {0-112}<01-11>, {1-102}<-1101>. The choice of the variant depends on the crystal orientation and direction of the shear stress. The most common model describing the twinning behaviour of Mg alloys is use of Schmid factor (SF) for calculation of grain possible twinning variants. Although there have been reported many deviations from the Schmid law for mechanical twinning, this model seems to be the most appropriate for description of simple {10-12} twinning in Mg.