KINEMATIC VORTICITY ANALYSIS RECONSIDERED
The Rs/Θ method provides meaningful estimates of Wm in high-strain zones developed from originally isotropic rocks that experienced strains of <20:1. At very large strain ratios the Θ angle is too low to resolve simple versus general shear deformation. The Rs/Θ method is valid for steady state and non-steady state deformations, constrictional and flattening strains, and volume changes. In mylonitic rocks with relatively low strains (<10:1), vorticity gauges that are based on the stable position of rigid clasts overestimate the simple shear component relative to the Rs/Θ and quartz c-axis methods. The porphyroclast hyperbolic distribution (PHD) method yields an estimate of the neutral kinematic vorticity number (Wn) and provides a measure of the last increments of rotational strain. PHD analysis of ultramylonitic rocks from a variety of tectonic settings reveal significant rotational strain along planes both parallel and normal to the elongation lineation. These data suggest triclinic deformation symmetries may be common.