Style of deformation and tectono-sedimentary evolution of fold-and-thrust belts and foreland basins: From nature to models

Orogenic systems, including their external fold-and-thrust belts and foreland basin systems, generally evolve from the inversion and imbrication of former continental margins. Continental margins are characterized by displaying along-strike variations in the degree of inherited regional extension (i.e., from limited lithospheric stretching to full necking, leading to mantle exhumation and oceanic accretion). These differences have a fundamental impact on the pre-shortening thermal state of the lithosphere and on structural style development. Indeed, one of the key processes in fold-and-thrust belts is the reactivation and inversion of pre-existing extensional faults. Inversion tectonics is widespread during the evolution of many orogens and this process can exert a strong control on the structural and mechanical evolution of fold-and-thrust belts (Lacombe and Bellahsen, 2016). The presence of evaporitic sequences interacting during lithospheric stretching and subsequent thermal subsidence is also a key parameter in the structural styles and deformation distribution of thrust sheets involving inverted basins and salt structures. On the other hand, deformation can also be transferred ahead and downward of the shallow deformation front, leading to frontal imbrication of deep seated structures in cratonic forelands or the sub-thrust region of active fold-andthrust belts. Defining the correct structural style of fold-and-thrust belts and understanding the controlling factors are necessary steps towards predicting their long-and short-term evolution, with implications for crustal/lithospheric rheology, mountain building processes and seismic hazard, and for the correct assessment of their potential for hydrocarbon exploration (e.g., Butler and Mazzoli, 2006; Lacombe et al., 2007; Poblet and Lisle, 2011; Lacombe et al., 2016). For these reasons, fold-and-thrust belts and adjacent foreland basin systems represent outstanding places to investigate (active) deformation and surface processes and the way these processes interact to shape mountain belts. On a short-time scale, the pattern of deformation of fold-and-thrust belts provides information on crustal mechanics, the sequence of active faulting and its relation to large earthquakes; on a long-time scale, the structure and dynamics of the fold-and-thrust belt -foreland basin systems offers unique insights into the influence of structural, thermal and rheological inheritance, together with coupling between surface and deep processes. During the last ten years, significant advances have been made in the description and understanding of fold-and-thrust belts and foreland basins. Among (many) others: better definition of structures at depth (seismic imaging, 3D visualization/ geomodelling, better appraisal of geometrical uncertainties); use of analogue and numerical modelling to constrain long-term and short-term surface and deep processes; applications of thermochronology (detrital thermochronology for sediment routing and paleo-burial estimates, coupled thermochronological and 2D/3D mechanical/kinematical modelling); recognition of the influence of salt and salt tectonics; renewed conceptualization of fold-fractures relationships and new ways to unravel paleostress history.