Strain partitioning and interplate friction in oblique subduction zones: Constraints provided by experimental modeling

摘要

Physical modeling of oblique subduction is performed to study the mechanism of strain partitioning. The model is two-layer and includes the elasto-plastic lithosphere (the overriding and subducting plates) and the low-viscosity liquid asthenosphere. The subduction is driven by a push force from a piston and a pull force when the density contrast Delta(rho) between the subducting plate and the asthenosphere is positive. We vary both Delta rho and the interplate friction (frictional stresses). Slip partitioning is obtained only in the models with high interplate friction and only when the overriding plate contains a weak zone. This zone in the models corresponds either to locally thinned lithosphere or to cut (fault). The horizontal, trench-normal component of the interplate friction force F-fh can be comparable with the absolute value of the horizontal component of the nonhydrostatic interplate pressure force F-Ph in the subduction zone. F-fh is always negative (compression), while F-Ph can be either negative (compressional subduction regime) or positive (extensional regime). High friction, which promotes partitioning, can completely cancel the extensional (suction) force F-Ph Back are tension and strike-slip faulting appear thus as conflicting processes, although they can coexist in the same subduction zone, depending on the relative values of relevant forces. It appears that high friction can exist only in compressional subduction zones where partitioning should develop more easily. This conclusion is supported by the comparison of two oblique subduction zones, having similar geometry: the compressional southern Kurile zone (strong partitioning) and extensional southern Ryukyu zone (no lithospheric-scale partitioning). Other factors controlling the strain partitioning are the length of the oblique subduction zone, the boundary conditions at the transverse limits of the forearc sliver, and of course, the obliquity of subduction. [References: 59]