Continental margin syn-rift salt tectonics at intermediate width margins

This paper examines interactions among syn-rift continental margin extension, evaporites, particularly rocksalt (halite), deposited in the overlying sedimentary basins, and clastic sediment loading. We present dynamically evolving 2D numerical models that combine syn-rift lithospheric extension, with salt (viscous halite, 10(18)-10(19) Pa s) and clastic (frictional-plastic) sediment deposition to investigate how salt is distributed and subsequently mobilized during syn-rift extension. Example results are shown, contrasting salt deposition in the early, mid and late syn-rift phases of a single lithospheric extension model. The lithospheric model is chosen to give depth-dependent extension and intermediate width margins with proximal grabens and a hyperextended distal region. The models exhibit diachronous migration of extension towards the rift axis and this is reflected in the faulting of overlying sediments. The models illustrate the roles of timing of salt deposition, relative to rifting and subsequent sedimentation, in defining the location and deformation of syn-rift salt, with post-salt sediment progradation in some models. Late deposition of salt leads to increased lateral extent of the original salt body and decreased variation in salt thickness. Seaward flow of salt increases with later deposition; early syn-rift salt is deposited and trapped in the grabens, whereas mid and late syn-rift salt tends to flow towards the distal margin or even over the oceanic crust. Prograding clastic post-salt sediments drive more substantial seaward movement of mid and late syn-rift salt. A numerical model of the Red Sea with evaporite deposition during the mid to late syn-rift period, preceded and followed by aggrading and prograding clastic sediment, shows reasonable agreement with observations from the central Red Sea.