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Salt Tectonics in Fold and Thrusts Belts: Examples From the Zagros, Pyrenees and Kuqa Basin


Salt plays a dominant role in the structural style of fold and thrust belts. In many mountain belts, such as the Zagros and the Pyrenees, deposition of the salt predates the contractional deformation. In other cases (Zagros, Pyrenees, Kuqa basin), the salt was deposited in the foreland basin during the deformation. Distribution of the pre-convergence salt is one of the main factors controlling the regional structural grain of fold and thrust belts, determining the existence of thrust salients and reentrants as well as major changes in structural style. In addition, pre-existing salt structures, mainly developed at passive margins, control the geometry of the subsequent contractional structures. Shortening of the salt structures results into diapir reactivation, squeezing, welding and afterwards the development of folds and thrusts. Position of the former diapirs with respect the fold and thrusts structures and the linkage between them is determined by the thickness of the mechanical beam folded above the salt detachment as well as the geometry of the previous salt structures. Most of the diapirs of pre-convergence salt observed in fold and thrust belts result from the reactivation of former diapirs. However, new diapirs can also form triggered by local extensional faults coeval with thrusting (for example extensional faults formed by longitudinal stretching or by extensional collapse), or by folding and erosion of inflated salt in the footwall of the main thrusts. Reactivated older structures show a different style, with a significant development of secondary welds as well as megaflaps. Salt deposited in foreland basins mostly result into the development of salt-cored detachment folds with limited amount of diapirs triggered by syn-orogenic erosion. In some occasions pre-orogenic and syn-orogenic salt horizons are overlapped, determining some characteristic structural features. Apart from multiple detachment features, such as disharmonic fault-related folds, salt structures from the lower salt horizon may trigger salt structures of the upper salt layer, giving rise to interference patterns. Field and seismic examples illustrate all these different structures and will be complemented by images from analogue models.