The development of fabric and anisotropy in mantle peridotites in natural shear zones of the New Caledonia ophiolite is being studied using a combination of electron backscatter diffraction and high-field anisotropy of magnetic susceptibility techniques to determine lattice preferred orientation. Electron backscatter diffraction provides an accurate measurement of lattice preferred orientation and yields information on slip systems and deformation temperatures. High-field anisotropy of magnetic susceptibility is a new method that provides the orientation of the fabric main axes and the degree of anisotropy by isolating the magnetic contribution of silicates. The high-field anisotropy of magnetic susceptibility method is considerably faster than electron backscatter diffraction and, therefore, allows mapping of deformation gradients at a higher resolution. The project is quantitatively establishing the degree of correlation between high-field magnetic anisotropy and mineral fabric anisotropy determined using electron backscatter diffraction and other well-established methods such as the universal stage technique. If successful, the new method will permit more rapid study of mantle fabrics over a large area, thus aiding interpretation of seismic anisotropy data from the mantle.
