SHEATH-FOLD-LIKE STRUCTURES IN PSEUDOTACHYLYTES

Sheath-fold-like structures in pseudotachylyte samples from a gold mine in the Witwatersrand Basin (South Africa) are explained by injections of frictionally produced silicate melt within the shear zone due to the formation of high and low pressure zones. If the shear zone geometry is known, the orientation of the fold closures can be used to determine the direction and the movement sense. However, if it is not possible to establish the shear zone geometry, only the azimuth of movement can be estimated from the orientation of the sheath-fold-like folds. The flow banding in these fault rocks is indicative of laminar flow, which suggests a low Reynold's number.