Many mountain belts show curved structural trends in plan-view. The origins and kinematics of these bends are crucial to understanding the tectonic evolution of orogenic belts. However, because orogenic curvature occurs at many different scales, there is an ongoing debate over the formation processes of orogenic belts. Curved orogenic belts are produced by geodynamic forces capable of causing shortening and eventual extension. These geodynamic forces include: 1) slab rollback, where slab retreat and shortening occur close to the trench and extend into the overriding plate (Malinverno and Ryan, 1986; Royden et al., 1987; Lucente and Speranza, 2001; Schellart et al., 2007); 2) gravitational collapse due to potential energy differences (Platt and Vissers, 1989; Carmignani and Klingfield, 1990); 3) orogen-perpendicular compression (Jolivet et al., 1990); and 4) orogen-parallel compression (i.e., extrusion tectonics), where bending or buckling occurs perpendicular to the long axis of the orogen and extension occurs behind the orogen (Faccenna et al., 1996; Mantovani et al., 2002; Johnston and Mazzoli, 2009). It is also important to note that the geodynamics of curved belts depend strictly on their size. Regional-scale curved belts are primarily controlled by lithospheric-scale phenomena (Beck, 1998; Platt et al., 2003; Hall et al., 2004; Jolivet and Faccenna, 2000). Conversely, small-scale arcs are controlled by frictional processes occurring at crustal levels (Davis et al., 1983).

The following types of curved belts can be identified based on their kinematics: 1) oroclines (or rotational arcs), which are originally linear and subsequently bend during a deformation event; 2) primary (or non-rotational) arcs, which acquire their curvature in the initial deformation (Carey, 1955; Marshak, 1988); and 3) progressive arcs, which develop their arcuate nature as they grow (Weil and Sussman, 2004).

The extent to which paleogeography and the architecture of colliding continental margins influence the curvature of an arcuate belt (Weil and Sussman, 2004) depends on the geometry and strength of the detachment horizon, the configuration of the sedimentary basin, the presence of strike-parallel variations in lithology and sedimentary thickness, the occurrence of buttressing (Macedo and Marshak, 1999; Weil et al., 2010; Mitra, 1997; Paulsen and Marshak, 1999), the presence of crustal-scale wrench-faults or indenters, and the geometry of the lithosphere (Marshak, 1988; Marshak et al., 1992; Cunningham, 1993; Platt et al., 2003; Hall et al., 2004; Jolivet and Faccenna, 2000; Schellart and Lister 2004). Small-scale arcs formed after the collision of an orogenic wedge with one or more foreland obstacles, have been paleomagnetically investigated. Such salients usually reveal an oroclinal-type rotation pattern, as observed in the Wyoming-Idaho belt (Schwartz and Van der Voo, 1984) and the Southern Pyrenees (Sussman et al., 2004).

The use of single datasets (e.g., structural data, paleomagnetism, and seismic reflection) to classify curved orogens is not enough to adequately explain their kinematic evolution and can lead to contradictory and incomplete interpretations. Using only geologic/structural data (Martínez Catalán et al., 2002) or paleomagnetic data (Stamatakos et al., 1996; Weil, 2006) have resulted in multiple contradictory interpretations of a primary or rotational arc for several curved belts, including the Appalachians and the Variscan mountain system. Contradictory interpretations also characterize the curved Northern Apennines belt. Although some authors support its primary nature (Channell et al., 1978; Eldredge et al., 1985; Muttoni et al., 1998), others suggest either an oroclinal origin for the outer portion of the arc (Speranza et al., 1997) or a progressive arc mechanism, which acquired its definitive curved shape during the Neogene Period (Calamita and Deiana 1988; Cifelli and Mattei, 2010). As a result, the rotational nature of this fold-and-thrust belt remains controversial.

In this paper, we attempt to explain the evolution of the outer Northern Apennines within the context of the Apennine-Maghrebide orogen. The Apennine-Maghrebide orogen can be divided into two arcuate features: the Northern Apennines Arc and the Southern Apennines-Calabrian Arc. They are characterized by differences in paleogeographic domains, stratigraphic successions, structural setting, and geodynamic evolution one respect to another (Satolli and Calamita, 2008, and references therein).

Our methodology includes the integration of geologic, structural, and paleomagnetic data collected in this belt over several decades of geological research. The integration of these data supports a thick-skinned setting of the belt, strongly controlled by the structural inheritance of older faults. These older faults are responsible for the orientation of thrust faults and the overall curved geometry.