Ritske S. Huismans

Continental rifted margins can be associated with widespread and thick salt deposits, which are often formed during the final stages of rifting, prior to breakup. These salt‐bearing margins are typically characterized by pronounced post‐rift salt tectonics with variable and complex structural styles and evolution. We use a lithosphere‐scale geodynamic numerical model to investigate the role of varying post‐rift sediment fluxes and progradation rates on rifted margin salt tectonics. We focus on a single, intermediate, rifted margin type and salt basin geometry to explore scenarios with different: (i) constant and (ii) time‐varying post‐salt sediment fluxes. We demonstrate that these promote significant contrasts in the style and magnitude of salt tectonics in the proximal, transitional and distal margin domains. The differences are primarily controlled by the relationship between the rates of sediment progradation ( V prog ) and salt flow ( V s ). When V prog > V s , the salt is rapidly buried and both vertical and lateral salt flow are suppressed across the entire margin. When V prog < V s , the salt flows vertically and seaward faster than sediments prograde producing major diapirism in the proximal domain and major distal nappe advance, but only moderate overburden extension and distal diapirism. When V prog ~ V s , there is moderate proximal diapirism and distal nappe advance, but major updip extension and downdip shortening, which produces major distal diapirism. Modelling results are comparable to various natural systems and help improve our understanding of the controls and dynamics of salt tectonics along salt‐bearing rifted margins.

Rifted passive margins exhibit a large variety in the timing, distribution, and amount of magmatism. The factors controlling magmatism during rifted margin formation, remain, however, incompletely understood, partly owing to the complex rifting styles. In this study, we use 2‐Dimensional numerical models to investigate the effects of depth‐dependent wide rifting and lithospheric counterflow on magmatism during rifted margin formation. Results show that a strong crust promotes narrow margins with a sharp transition to normal thickness oceanic crust whereas a weak crust promotes depth‐dependent wide rifting, with preferential removal of mantle lithosphere, leading to formation of wide margins with over‐thickened (>18 km) igneous crust in the distal margin. Counterflow of depleted lithospheric mantle, in contrast, may delay syn‐rift magmatism, and result in exhumed a‐magmatic continental mantle at narrow margins. The combination of wide rifting and lithospheric counterflow results in magma‐poor wide margins, with in some cases a transition to excess magmatic activity at breakup. Our models provide an explanation for the contrasting magmatic productivity at narrow and wide rifted margins, such as observed in the Lofoten‐Vesterålen, Newfoundland, Kwanza Basin, and Orange Basin margins.