Deformation path in high-strain zones, with reference to slip partitioning in transpressional plate-boundary regions

The current status of the kinematics and strain geometry of high-strain zone studies is briefly summarized. A general high-strain zone has a triclinic deformation path, and monoclinic shear zones are special end member cases. Fabrics observed in natural shear zones and theoretical considerations based on continuum mechanics are compatible with this conclusion. Non-steady deformation paths remain difficult to deal with, and may ultimately rely on a realistic mechanical treatment of high-strain zones which may be possible when our knowledge of the mechanical behavior of rocks under natural deformation conditions is improved. An examination of the phenomenon of slip partitioning in transpressional plate boundary regions shows that the bulk deformation path in the forearc area (trench-parallel high-strain zone) is generally triclinic. The Alpine Fault in the South Island of New Zealand provides an example of a currently active triclinic shear zone. The Southern Knee Lake shear zone of Manitoba, Canada, provides an Archean example of a triclinic shear zone.