SLIP PARTITIONING AND DEFORMATION LOCALIZATION IN OBLIQUELY CONVERGENT SETTINGS AS A RESULT OF FABRIC BUILDUP: AN INVESTIGATION BASED ON MICROMECHANICS

In obliquely convergent settings, the net boundary movement between bonding blocks or plates is commonly accommodated by a boundary-orthogonal pure shearing, which affects a broader zone and leads to crustal thickening, and a boundary-parallel simple shearing which remains localized in some major transcurrent zones parallel to the strike of the system. This phenomenon has been called slip partitioning, the cause of which is still poorly understood. In this presentation, a self-consistent micromechanical approach is applied to investigate the evolving strength of the convergent system as a result of fabric buildup during deformation inside the system. The approach is based on an extension of Eshelby’s inhomogeneity solution to non-Newtonian power-law viscous materials and micromechanical homogenization methods. The lithospheric scale deformation in the obliquely convergent system is represented by inclined transpression. As a result of fabric and therefore rheological anisotropy buildup during progressive deformation, the system weakens with respect to the boundary-parallel simple shearing deformation and hardens with respect to the boundary-orthogonal pure-shearing. In order to accommodate the ongoing net oblique boundary movement, the progressively hardening system due to boundary-orthogonal movement tends to spread the crustal thickening to a broader deformation zone whereas the progressively weakening system due to boundary-parallel (largely strike-slip) movement can readily be accommodated, throughout deformation, in localized zones. For steeply dipping zones undergoing oblique convergence, it is found that deformation in lower angle convergent systems, with the boundary movement direction less than 15 degree from the zone strike, can remain localized while deformation in higher angle convergent systems will show deformation partitioning.