Strain partitioning and localization due to detachment heterogeneities in fold-and-thrust belts of progressive arcs: results from analog modeling

Abstract

Although most arcuate orogens are deformed as progressive arcs—curvature is acquired during shortening-, they have been scarcely simulated by analog modeling. To investigate factors that control the growth of progressive curves in fold-and-thrust belts, we developed seven analog models where the backstop shape changed over time, and distinctive geometric heterogeneities were set in the detachment layer. These heterogeneities, often described in natural cases, include diapirs, thickness lateral variations (including pinch-outs) of the viscous detachment layer as well as frontal pinch-outs. Our results show that strain was partitioned between shortening structures showing radial transport directions, and both normal and oblique strike-slip faults that accommodated arc-lengthening. The location of any heterogeneity conditioned the nucleation of structures and thus, the wedge evolution and its resulting geometry. The presence of both diapirs and frontal silicone pinch-outs favored the stagnation of the deformation front, and the subsequent wedge thickening up to reach the supercritical angle. Both diapirs and thickness lateral variations of the viscous layer localized arc-parallel stretching. In addition, their configuration determined the amount and distribution of salients and recesses along the arcuate belt, diapirs and more frictional detachments favoring thicker wedges and less frontal propagation. The differential displacement between salients and recesses was accommodated by strongly partitioned transfer zones, localized by the boundaries between distinctive detachment domains. These results may be useful to investigate geometric and kinematic changes along natural progressive arcs such as the Gibraltar, Sulaiman and Zagros cases.