Numerical analysis with FLAC is used to identify how flow and its variation associated with folding is governed by mechanical properties of the layers, imposed strain rates, and initial geometrical irregularities. An investigation of the vorticity history of likely folding paths shows that spherical porphyroblasts are expected to rotated little with respect to the axial plane of the fold, explaining the universal observation made in the last 15 years that porphyroblasts exhibit more or less constant orientation across hosting fold limbs. Tectonic overpressure is an old problem in geology. The concept is simple. The difference is referred to as tectonic overpressure , because it arises wholly from tectonic deformation.
Many geologists hold the belief that rocks are too weak to support high overpressures .
However, this statement is justifiable only in Andersonian stress environments that do not include high-strain zones. If indeed it can be demonstrated that high overpressures can be generated as well as dynamically maintained in certain tectonic environments, the conclusion has radical implications. Greenstone Belt Greenstone belts are common in the Superior province and, for reasons that are largely unclear, they are usually associated with high-strain zones. One set is NE trending and the other ESE trending. Both sets seem to be overprinted by a NNE fabric that is parallel to the northwest Superior boundary.