Geometry and kinematics of fault-propagation folds with variable interlimb angle Majed Jabbour a , Damien Dhont a, * , Yves Hervouët a , Jean-Paul Deroin b a Université de Pau et des Pays de l’Adour, UMR 5150: Laboratoire desFluides Complexes et leurs Réservoirs, CNRS-UMR-TOTAL, Avenue de l’Université, BP 1155, 64000 Pau, France b Université de Reims Champagne-Ardenne, UFR Sciences Exactes et Naturelles, Département des Sciences de la Terre, GEGENAA, EA 3795, 2 esplanade Roland Garros, 51100 Reims, France article info Article history: Received 22 March 2011 Received in revised form 30 April 2012 Accepted 2 May 2012 Available online 13 June 2012 Keywords: Fault-propagation fold Variable interlimb angle Modelling Kinematics Folding abstract Several conceptual approaches have been proposed to account for the development of fault-propagation folds whose geometry and kinematics depend on the amount of displacement along a basal decollement level, the ramp angle and the slip to propagation ratio. Among these, the variable interlimb angle model of Mitra (1990) is able to explain open and close natural folds but its application is limited because the fold geometry and bed thickness evolution rely on imposed parameters that cannot be measured directly. Here, we use the ramp and the interlimb angles as input data to develop a forward fold model that accounts for thickness variations in the forelimb. The relationship between the fold amplitude and fold wavelength is subsequently applied to construct balanced geological cross-sections from surface parameters only and to propose a kinematic restoration of the folding through time. The model can catter for a wide variety of folds, reconstruct the deep architecture of anticlines and deduce the kinematic evolution of the folding with time. We consider three natural examples to validate the variable interlimb angle model. Along-strike thickness variation in the forelimb of the Turner Valley anticline in the Alberta foothills of Canada precisely corresponds to the theoretical values proposed by our model. Reconstruc- tion at depth of the Alima anticline in the southern Tunisian Atlas implies that the decollement level is localised in the Triassic-Liassic series, as highlighted by seismic imaging. The kinematic reconstruction of the Ucero anticline in the Spanish Castilian mountains is also in agreement with the fold geometry derived from two cross-sections. The variable interlimb angle model predicts that the fault-propagation fold can be symmetric, normal asymmetric (with a greater dip value in the forelimb than in the back- limb), or reverse asymmetric (with greater dip in the backlimb) depending on the shortening amount. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Fault-propagation folds are common features in foreland basins and fold-and-thrust belts (e.g., Suppe, 1983, 1985; Jamison, 1987; Suppe and Medwedeff, 1984, 1990; Mitra, 1990; Mercier, 1992; Philippe, 1994; Outtani et al., 1995; Martin and Mercier, 1996; Mercier et al., 1997; Erslev, 1991; Hardy and Ford, 1997; Allmendinger, 1998; Cristallini and Allmendinger, 2002; Tavani et al., 2006; Torres Carbonell et al., 2008). Fault-propagation folds commonly develop above an upward propagating thrust ramp as a consequence of the horizontal displacement of the sedimentary pile above a decollement level. The shape of the fault-propagation fold therefore depends directly on both the amount of displace- ment along the basal decollement level, the dip angle of the ramp and the slip to propagation ratio (e.g., Suppe, 1983, 1985; Suppe and Medwedeff, 1984, 1990; Mitra, 1990; Mercier et al., 1997). The self-similar and the time-variant models represent the two main quantitative kinematic approaches used for the geometric evolution of the fault-propagation folds associated with a flat decollement (Fig. 1). The self-similar models assume no forelimb rotation during the folding, implying that the fold geometry remains constant while the anticline is growing above the ramp (Suppe, 1983, 1985; Suppe and Medwedeff, 1984, 1990; Chester and Chester, 1990; Mercier et al., 1997)(Fig. 1a). Such models have been applied to describe the distribution of the deformation during the folding (Storti and Salvini, 1996; Hedlund, 1997; McConnell et al., 1997; Salvini and Storti, 2001; Masini et al., in press) and to reconstruct the shape of anticlines from field measurements and/or seismic profiles (e.g., Mount et al., 1990; Al Saffar, 1993a, b; Outtani et al., 1995; Mercier et al., 1995; Labrousse, 1998; Labrousse and Hervouët, 1999; Ahmadi, 2006; Ahmadi et al., 2006; Jabbour et al., 2007). The time-variant kinematic models consider that the fold tightens in relation with the rotation of its forelimb with * Corresponding author. Now at: TOTAL, Avenue Larribau, 64000 Pau, France. Tel.: þ33 0 5 59 83 5103. E-mail address: damien.dhont@total.com (D. Dhont). Contents lists available at SciVerse ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg 0191-8141/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsg.2012.05.002 Journal of Structural Geology 42 (2012) 212e226