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

The current status of the kinematics and strain geometry of high-strain zon e studies is briefly summarized. A general high-strain zone has a triclinic deformation path, and monoclinic shear tunes are special end member cases. Fabrics observed in natural shear zones and theoretical considerations bas ed on continuum mechanics are compatible with this conclusion. Non-steady d eformation paths remain difficult to deal with, and may ultimately rely on a realistic mechanical treatment of high-strain zones which mag; be possibl e when our knowledge of the mechanical behavior of rocks under natural defo rmation conditions is improved. An examination of the phenomenon of slip pa rtitioning in transpressional plate boundary regions shows that the bull; d eformation path in the forearc area (trench-parallel high-strain zone) is g enerally triclinic. The Alpine Fault in the South Island of New Zealand pro vides an example of a currently active triclinic shear zone. The Southern K nee Lake shear zone of Manitoba, Canada, provides an Archean example of a t riclinic shear zone. (C) 2001 Elsevier Science Ltd. All rights reserved.