3-D rock salt fabrics in a shear zone (Sْria Anticline, South-Pyrenees)

The internal geometry of the evaporitic horizons serves as a good indicator of their large-scale behaviour. However, the determination of the strain ellipsoid inside the deformed salt bodies can often be difficult. Moreover, the relationship between the bulk strain ellipsoid and the grain shape ellipsoid is not straightforward, and two parameters, orientation and the dimension of the grain shape ellipsoid, need evaluation. The grain shape ellipsoid is not an indicator of the dimensions of the bulk strain ellipsoid. The increase in shear strain led initially to a growth in grain volume followed by a reduction to a value near the original volume, specifically due to the long axis change. The orientation of the grain shape ellipsoid runs parallel to that of the strain ellipsoid after a certain amount of deformation. These changes were accompanied by the growth of a new tectonically oriented grain population. The rapid spatial changes in morphology contrast with the constant and strong {100} texture. The intracrystalline deformation mechanism consistent with this texture is the {110}〈110〉 slip system. Nevertheless, a mechanism such as fluid assisted grain boundary migration might have also taken place to account for the grain volume changes.