Along-strike variation of orogenic wedges associated with vertical axis rotations

[1] Analogue experiments with variable along-strike shortening were performed by pushing a rotating rigid backstop against constant thickness one-layer (sand) and two-layer (sand-silicone) cakes. Along-strike shortening differences were introduced by the vertical axis rotation of the backstop and caused lateral variations in the deformational style of the accretionary wedge. Deformational fronts were diachronous and oblique with respect to the backstop direction. Numerous oblique ramps developed in order to accommodate the structural differences between sectors with different amounts of shortening, individual thrust sheets rotated significantly less than the backstop, and older thrust sheets presented higher vertical axis rotations than younger ones. Analogue models show the importance of strike-slip motions during thrusting and significant vertical axis rotations in frictional and ductile basal conditions, respectively. Our modeling results are compared with natural examples from the southern Pyrenees, the Idaho-Wyoming thrust belt, and the Transverse Ranges, where external axis rotations are linked to oblique ramps, differential shortening, and thrust propagation in orogenic wedges.