MAJOR INTRACONTINENTAL STRIKE-SLIP FAULTS AND CONTRASTS IN LITHOSPHERIC STRENGTH

Most major (but not all) intracontinental strike-slip faults lie adjacent to relatively strong regions, such as oceanic lithosphere or Precambrian shields. (For our purpose, such faults are considered major if slip rates equal or exceed ~10 mm/yr.) We argue that such faults form adjacent to discontinuities in strength, because strain in a continuous medium must concentrate near such strong objects. Moreover, that concentration of strain is enhanced in deforming continua where strain rates vary with deviatoric stress raised to a power n > 1 (where viscosity is non-Newtonian), as is the case for rock-forming minerals at the low temperatures characteristic of the strong part of the lithosphere. Where deformation is spread over a wide region, however, such as in the Basin and Range Province of the western United States or in the high interior of the Tibetan Plateau, the absence of strong objects may allow deformation to be diffuse without major strike-slip faulting.