Calcite texture development in experimentally induced ductile shear zones

Specimens of fine grained micritic limestone were deformed in plane strain geometry in pure shear, a combination of simple and pure shear, and in simple shear. Temperatures were 400° C and 500° C, confining pressure was 100 MPa. In the experiments with a simple shear component strain is concentrated and approximately homogeneous in a 2–3 mm wide shear zone. Shear displacement is documented by marker lines and circles. Shear strain γ varies between 0.84 and 1.56. Strain is recorded by flattening of individual grains, defining a foliation normal to the axis of principal finite shortening ε ₁. No twinning is observed on a macroscopic scale. X-ray and neutron diffraction techniques were used to characterize texture before and after deformation. All specimens display strong preferred orientation as documented by 0006, 10¯14 and 11¯220 pole-figures, c axes pole-figures display three maxima in the ε₁–ε₃ plane. If the axes of the strain ellipsoids are used as a coordinate system textures in pure and simple shear are similar but there is considerable monoclinic distortion in simple shear which is attributed to the noncoaxial strain path.