Textures in experimentally deformed olivine aggregates: The effects of added water and melt

The texture development in experimentally sheared aggregates of olivine was monitored as a function of increased water content and added melt. In dry samples, an alignment of {010} with the shear plane and 〈100〉 and 〈001〉 with the shear direction, respectively, was observed, consistent with intracrystalline glide on the (010)[100] and (010)[001] slip systems. Samples with high water content showed consistently stronger textures of the (010)[100] component for comparable shear strains indicating that water may especially ease glide on this slip system. Samples with added melt showed an increased alignment of {010} and 〈001〉 subparallel to shear plane and shear direction respectively, whereby the maxima were consistently rotated 10 to 20° against the sense of shear. This type of texture can be explained by a combination of increased glide on the (010)[001] slip system in combination with a partitioning of the strain between melt rich bands and relatively melt free regions in the sample. Physical anisotropies calculated from the textures indicate that increased water content causes enhanced anisotropy for longitudinal and transverse seismic waves. The addition of melt on the other hand may change the type of anisotropy that develops during deformation, but does not significantly change the magnitude of anisotropy compared to samples of pure olivine.