Contents lists available at ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg Structural evolution of salt-influenced fold-and-thrust belts: A synthesis and new insights from basins containing isolated salt diapirs Oliver B. Duffy a,∗ , Tim P. Dooley a , Michael R. Hudec a , Martin P.A. Jackson a , Naiara Fernandez a , Christopher A-L. Jackson b , Juan I. Soto c a Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX, 78713-8924, USA b Basins Research Group (BRG), Department of Earth Science & Engineering, Imperial College, Prince Consort Road, London, SW7 2BP, United Kingdom c Departamento de Geodinamica and Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Universidad de Granada, Campus Fuentenueva, 18071, Granada, Spain ARTICLE INFO Keywords: Salt tectonics Shortening Fold-and-thrust belts Diapirs Minibasins Zagros Gulf of Mexico ABSTRACT Lateral shortening is expressed in unique ways in salt basins, especially if pre-shortening diapirs are present. We present an overview of previously-published and new physical models and present new 3-D conceptual models that capture the evolution of shortening structures in salt provinces dominated by precursor isolated diapirs (termed isolated-diapir provinces). In such provinces, isolated diapirs form only a minor volumetric component of a sedimentary basin, however, due to the relative weakness of rock salt and their ability to localize strain, during shortening they have a disproportionately large influence on structural development. We find three key mechanical principles govern the processes and structural styles developed during short- ening of isolated-diapir provinces. First, salt diapirs shorten before surrounding sedimentary rocks due to their relative weakness, and so form salients in the thrust front during early shortening. Second, diapirs tend to nucleate folds and faults, which radiate out from the diapirs. Third, as diapir walls converge, the roof must shorten. Extrusive salt sheets are expelled through thin roofs, but thicker roofs resist piercement and so tend to undergo complex folding and faulting. As a result of these principles, the first-order controls on the structural styles expressed across a shortened isolated-diapir province are the configuration the diapir array prior to shortening, the connectivity of these diapirs prior to shortening, total strain magnitude, and diapir roof thickness. Second-order controls include the initial cross-sectional and map-view geometry of diapirs, diapir size, and diapir orientation with respect to the shortening direction. 1. Introduction The geometry and kinematics of fold-and-thrust belts are generally well understood as a result of their spectacular exposure in mountain ranges around the world (e.g., Bally et al., 1966; Dahlstrom, 1969; Boyer and Elliott, 1982). A relatively poorly-understood aspect of these systems involves fold-and-thrust belts that detach on, and are influ- enced by mobile salt. In these settings 3-D shortening styles can be particularly complex and diverse due to: i) salt being much weaker than local sedimentary rocks, creating a strength anisotropy during short- ening; and ii) the ability of salt to flow and thus be heterogeneously distributed prior to the onset of shortening (e.g. Davis and Engelder, 1985; Letouzey et al., 1995). Thus, the configuration of salt prior to shortening exerts a major control on salt-detached structural styles, with three styles standing out. In the first and simplest case, bedded salt is undeformed, forming a continuous gently-dipping layer prior to shortening. In this situation, where shortening occurs with no precursor salt structures present, the salt simply acts as a décollement, ‘lubricating’ predominantly linear fold-and-thrust belts above that show extremely low taper angles (e.g. Davis and Engelder, 1985; Letouzey et al., 1995; Morley et al., 2011) (Fig. 1a). Common structural styles observed in such settings are salt- bearing thrusts, box folds, and long-wavelength, broad anticlines se- parated by narrow, sharp synclines (Fig. 1a). In general, there is little along-strike variability in structural style, aside from those developed due to along-strike variations in the depositional thickness of the salt (e.g. Davis and Engelder, 1985). Contractional provinces in which salt acts primarily as a detachment include the Valley and Ridge Province of the Appalachians (e.g. Frey, 1973), the Betics and Rif (e.g., Flinch and Soto, 2017), the Pyrenees (e.g., Canérot et al., 2005; Roca et al., 2011; https://doi.org/10.1016/j.jsg.2018.06.024 Received 30 April 2018; Received in revised form 28 June 2018; Accepted 29 June 2018 ∗ Corresponding author. E-mail address: oliver.duffy@beg.utexas.edu (O.B. Duffy). Journal of Structural Geology 114 (2018) 206–221 Available online 02 July 2018 0191-8141/ © 2018 Published by Elsevier Ltd. T