Texture development of polycrystalline anhydrite experimentally deformed in torsion

Abstract

A polycrystalline aggregate of anhydrite was deformed in torsion to a maximum shear strain of 8.1 at 700°C and a maximum shear strain rate of 5×10^–3 s^–1. The crystallographic preferred orientation (CPO or texture) was investigated as a function of shear strain/shear strain rate in a radial profile from the centre to the edge of the sample. A deformation texture developed at shear strains of 1.5–2 (corresponding to shear strain rates of 1 to 1.3×10^–3 s^–1) and reached a stable position relative to the kinematic frame at a shear strain of 3.7 (2.3×10^–3 s^–1). Further shear strain only led to a small increase in texture strength but no change in the orientation relative to the kinematic frame. The CPO is very similar to naturally observed textures and can be explained by the activity of the {001}<010> and {012}<121> slip systems. Although independent mechanical data indicate that a change of mechanism from dislocation- to diffusion-controlled creep occurred at a shear strain of approximately 1.5, the texture does not weaken, but rather increases, in strength with higher shear strains.