Folding and fracturing of rocks adjacent to salt diapirs

This review paper examines deformation adjacent to salt stocks and walls and beneath salt sheets, with a focus on passive salt rise or emplacement and structures ranging from large-scale folds and faults to small-scale folds, fractures, and shear zones. The analysis begins with a summary of the existing literature on physical and numerical modeling and empirical subsurface and outcrop data, which offer conflicting interpretations and models. The emphasis here, however, is on exposed diapirs and sheets in a variety of salt basins. These demonstrate that near-salt deformation during passive diapirism is less common and less pronounced than is typically thought. In most cases, diapir rise and sheet emplacement do not directly shear and fracture adjacent strata. Instead, salt movement leads to drape folding of a thin roof, which in turn may cause associated fracturing, just as with folding of any origin. There can be exceptions, with the most common being regional extensional, contractional, or strike-slip deformation that is coeval with or postdates diapirism. This is especially the case if the salt becomes welded and there is ongoing weld-parallel slip or if fault damage zones formed away from diapirs subsequently become juxtaposed against the salt by ongoing slip.