Abstract

The differential rotation about a vertical axis across a southeast-vergent recumbent fold and thrust fault within a single nappe from the eastern Subbetic zone of southern Spain has been determined using paleomagnetism. The upper limb has rotated clockwise by 68° ±22° relative to the lower limb. Mapping of the structure indicates that the syncline is an isoclinal fold in the northeast and an open fold in the southwest. The differential vertical-axis rotation across this structure appears to have been accommodated by a pro- gressive increase in along-strike horizontal shortening, reaching 8.5 km at 3.7 km from the pivot point. This differential shortening and the rotation are probably the result of increased drag on the underlying thrust close to the pivot point compared to the farthest extent of the structure. The lateral boundary of the rotating sheet is a sinistral strike-slip fault, which is consistent with the rotational geometry. Pinning is probably enhanced by lateral heterogeneities within the stratigraphy. This result ties rotational deformation to early-middle Miocene folding and thrusting, rather than to late Miocene- Holocene strike-slip deformation. Rotation by pinning of thrust sheets may prove to be an important aspect of deformation in many fold and thrust belts.

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