The effect of convergence angle on the kinematic evolution of strain partitioning in transpressional brittle wedges: Insight from analog modeling and high-resolution digital image analysis.

Using analog modeling aided by digital image analysis (DPIV), we constrained the long-term kinematic evolution of strain partitioning in transpressional brittle wedges as a function of convergence angle. We ran a series of dry quartz sand experiments representing highly oblique continent-continent collision (convergence angles of 4° to 30°). The digital image analysis provided high-resolution constraints on the long-term kinematic evolution of these wedges, which could be subdivided in distinct kinematic stages, comprising (1) an initial 'distributed strain' stage and (2) an 'oblique wedge' stage before (3) the stage of strain partitioning is reached. Thus, we document the evolution of different deformation stages from a single plate tectonic boundary condition. In addition, the relationship between convergence angle, kinematic stages, and wedge geometry (including fault dips and fault hierarchy) was established. The modeling results show that smaller convergence angles lead to steeper faults. Besides, for a constant convergence angle, the proshears that evolved during the strain partitioning stage were less steep than those formed during the oblique wedge stage. The fault slip vector on individual fault segments was derived from the DPIV data set for each time increment, quantifying the magnitude and orientation of slip on fault segments during the different kinematic stages. In addition, in the 7.5° and 15° models, rotation of the slip vector by up to 40° was observed on a single proshear during the strain partitioning stage. These observations allow to some degree a validation of existing analytical models of strain partitioning, in particular the assumption of steady state. [ABSTRACT FROM AUTHOR]