The geometry of the Apennine fold-andthrust belt has been strongly infl uenced by the original architecture of the Adria paleo margin. In the Central Apennines, pre-thrusting normal faults (pre-orogenic Permian(?)/TriassicJurassic and synorogenic Neogene) were reactivated with compressional kinematics during the Neogene-Quaternary orogenesis.We present a study on the control of preexist ing extensional faults on thrust tectonics in the Central Apennines. We describe positive inversion geometries of some salient fold-and-thrust structures (Setteporte, the Sabini Mountains, the Sibillini Mountains, Montagna dei Fiori, the Gran Sasso range, Maiella Mountain, and Casoli-Bomba) by integrating surface geological data and seismic-line interpretation. In these structures, different styles of fault reactivation depend on their orientation with respect to the subsequent compressional NE-SW-trending stress fi eld. The NW-SE-and WNW-ESEtrending pre-thrusting normal faults in the backlimbs of the anticlines were displaced and passively translated in the hangingwall blocks of the thrust planes, thus exhibiting a classical shortcut geometry (shortcut anticlines). Differently, pre-orogenic normal faults in the N-S-trending anticlines were reactivated in a transpressive deformational context, as docu mented by the mainly dip-slip and strike-slip kinematics along the thrusts and back thrusts, respectively (reacti vation anticlines).The cases studied document differences in geometry in fold-and-thrust structures related to the trend of preexisting extensional faults, showing that different reactivation geom etries linked to the same inversion event can coexist at regional scale in curved foldand-thrust belts. The proposed inversion tectonic model and the resulting geometry of the fold-and-thrust belt could possibly be applied to analogous orogenic belts.

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Terra Nova, 24, 396–406, 2012 Abstract Fault‐bend and fault‐propagation folds have unique profiles in foreland fold‐and‐thrust belts that are caused by different fault‐related folding models and controlled by the mechanical characteristic of the multilayer and/or by reactivation of normal faults in a positive inversion tectonics context. In this work, NNE–SSW‐ and NW–SE‐trending anticlines, related to the Neogene curve‐shaped Olevano‐Antrodoco‐Sibillini thrust (Northern Apennines, Italy), are investigated to reconstruct fault‐related folding mechanisms. Geological and structural analysis allows us to interpret the NNE–SSW‐trending anticlines as fault‐bend reactivation folds and the NW–SE‐trending anticlines as fault‐propagation shortcut anticlines. The coexistence of fault‐bend and fault‐propagation folding processes involving the same multi‐layered succession in different arms of a curve‐shaped thrust is explained in an inversion tectonics context. This along‐strike variation of different folding mechanisms might be recognised in similar curve‐shaped orogenic thrust‐belts controlled by structural inheritance.

Low-angle faults that juxtapose younger rocks over older ones are widely documented in fold-thrust belts, and reconstruction of tectonic style is strictly dependent on their interpretation. Various modes exist for generating hinterland-dipping low-angle faults with younger-on-older relationships. Indeed, in the Central Apennines of Italy, the hinterland-dipping younger-on-older low-angle faults, which rest on the summits of the major anticlines (i.e., summit low-angle faults), have been interpreted variously as younger-on-older thrusts within out-of-sequence thrust systems, postorogenic normal faults, gravity-driven slides, or as rotated prethrusting normal faults. In this study, we provide a new and robust structural-geological data set, corroborated with stratigraphic timing constraints and balanced geological cross sections, bringing an essential contribution to the interpretation of the hinterland-dipping younger-on-older low-angle faults as preexisting normal faults rotated within the shortcut anticlines during the Neogene thrust-related fold emplacement. A detailed geological and structural characterization carried out on four remarkable examples from the Central Apennines allowed reconstructing an inversion tectonics model. The lack or reverse reactivation of the rotated prethrusting normal faults here analyzed is consistent with fault bend and fault propagation folding models associated with break forward in-sequence thrust propagation implying more conservative estimates of shortening for the Central Apennines thrust system, compared to the previous out-of-sequence models. Taking into account the various possible causes for the development of hinterland-dipping younger-on-older low-angle faults, the structural-geological characterization presented in this study and the results achieved could be critically applied when examining similar structures in other thrust belts.

The Caledonian and Variscan orogens in northern Europe and the Alpine-age Apennine range in Italy are classic examples of thrust belts that were developed at the expense of formerly rifted, passive continental margins that subsequently experienced various degrees of post-orogenic collapse and extension. The outer zones of orogenic belts, and their adjoining foreland domains and regions, where the effects of superposed deformations are mild to very mild make it possible to recognize and separate structures produced at different times and to correctly establish their chronology and relationships. In this paper we integrate subsurface data (2D and 3D seismic reflection and well logs), mainly from the North Sea, and structural field evidence, mainly from the Apennines, with the aim of reconstructing and refining the structural evolution of these two provinces which, in spite of their different ages and present-day structural framework, share repeated pulses of alternating extension and compression. The main outcome of this investigation is that in both scenarios, during repeated episodes of inversion that are a characteristic feature of the Wilson cycle, inherited basement structures were effective in controlling stress localization along faults affecting younger sedimentary cover rocks.