Curvilinear fault-bend folding: geometrical, kinematical and deformational implications.

Fault-bend folding is a common folding mechanism in thrust and fold belts worldwide. The widely used kink-band geometric model of fault-bend folding (Suppe, 1983) necessitates complex ramp segmentations to reproduce the rounded shape of many natural thrust related anticlines. Curvilinear hinge sectors provide a geometric and kinematic alternative solution to kink bands for modelling curved-hinge folds. We developed an analytical solution for modelling fault-bend folding using circular hinge sectors, named curvilinear fault-bend folding. The velocity field of this kinematic solution is different from that associated to the classical, kink-style model. Our solution predicts the development of curvilinear anticlines above staircase fault geometries and the occurrence of diachronous limb rotation in the forelimb (Step I) and in the crest (Step I). Different kinematic evolution of curvilinear fault-bend folding with respect to the classical kink-style model, implies different growth strata pattern and different expected deformation distribution. In particular, the development of rotational syngrowth wedges on both the forelimb and the crest of curvilinear fault-bend anticline is predicted, while it is neglected in the kink-style model (e.g. Suppe et al., 1992). Comparison between expected deformation pattern in the two model, when an homogeneous mechanical stratigraphy is assumed, show how deformation intensity in curvilinear fault-bend folding is lower than that expected in the kink-style model, and it is dependent on both the layer parallel and layer orthogonal position, whereas in the kink-style model it is dependent only on the layer-parallel position.ReferencesSuppe, J., 1983. Geometry and kinematics of fault-bend folding. American Journal of Sciences. 283, 684-721.Suppe, J., Chou, G.T., Hook, S.C., 1992. Rates of folding and faulting determined from growth strata. In: McClay, K.R. (Ed.), Thrust Tectonics. Chapman abd Hall, London, pp. 105-121.