Abstract The kinematics of regional-scale salt flow in the northern Gulf of Mexico is analysed using: (i) a map of shelf-break contours at the termination of successive depositional episodes; (ii) the location and geometry of large-scale structures of the slope domain as imaged by seismics; and (iii) digital slope bathymetry. In the north margin, salt has flowed towards the SW since the Cretaceous with three main stages of development prior to, during and after a massive salt extrusion in the Early Miocene time. The corresponding sequence of structural development is discussed using a laboratory model. Contrary to all previous interpretations that invoked sedimentary loading as the main driving force, the analysis of regional-scale salt flow implies that the salt tectonics of the northern Gulf of Mexico is predominantly controlled by gliding above the margin dip. The SW-directed salt flow indicates that the north margin of the northern Gulf of Mexico trends NW–SE, in agreement with plate kinematic models in which the Yucatan continental block has undergone a 45–60° dextral rotation relative to its present orientation.

Abstract Along the Angolan margin, the post-rift structural framework of which is strongly influenced by salt tectonics, a number of hydrocarbon reservoirs that are located above the Aptian salt have been charged by presalt source rocks of lacustrine origin. The paper examines the deformation mechanisms that can lead to windows in the salt layer able to provide pathways for hydrocarbon migration. It is shown that extension, due to gravity driven deformation, leads to cover-basement contacts in the sealed, tilted block sub-domain that occurs in the upper part of the margin. Once created, these contacts represent “permanent windows” in the salt layer. In the neighboring rollover sub-domain, the salt layer is also strongly thinned, but more homogeneously, preventing the formation of cover-basement contacts. The analysis of seismic sections shows that in absence of direct observation (e.g. , well data) active faulting can provide extremely useful criteria to detect the presence of salt layers too thin to be seismically imaged. The possibility that basement faults cutting through the salt layer could provide “transient windows” cannot be excluded. In the Angolan margin, the supra-salt hydrocarbon reservoirs charged by pre-salt source rocks are mostly located in the sub-domain of sealed, tilted blocks. As indicated by analog modeling, this domain is the most favorable for the creation of permanent windows in the salt layer. It is therefore suggested that hydrocarbon migration from pre- to postsalt sediments is strongly dependant on the significant salt layer thinning and penetration in the sealed tilted block sub-domain.

We use a thermomechanical modeling approach to study the development of extensional gneiss domes in a thickened and thermally relaxed lithosphere. Our models consider a compositional and thermally dependent rheological lithosphere layering, with a 60-km-thick crust and Moho temperatures in the range 840–1040 °C. No discontinuity or detachment fault is assumed to preexist within the upper crust. However, to initiate localized deformation, a density anomaly is placed at the base of middle crust. Extension is applied to one model boundary at constant rates of 2.0 and 0.66 cm/yr. Models illustrate the progressive development of domes and associated strain patterns at crustal scale. Extension first localizes in the upper crust as a nearly symmetrical graben, allowing the underlying middle and lower ductile crust to rise up, initiating a dome. Dome amplification is further accommodated by convergent channel flow in the lower crust. Strain localization displays a complex pattern of shear zones at the crustal scale, first nearly symmetrical, and progressively becoming asymmetrical, giving, in particular, an upward convex detachment on one side of the dome. During extension, Moho geometry and depth vary as a function of boundary displacement rate. At the lower boundary displacement rate used in the calculations, the Moho remains rather flat and rises up at a constant rate. Results are discussed in the light of field examples and compared to previous models.

Abstract 2D deformation experiments on multilayer models of a brittle-ductile lithosphere are reviewed. The experimental method consists of simulating simplified strength profiles which incorporate brittle (frictional) and ductile (viscous) rheologies with gravity forces. A selection of models built with sand and silicone putties to represent brittle and ductile lithosphere layers, respectively, is used to illustrate the effects of variations in strength profiles on deformation patterns. Models of extension first consider lithosphere necking and the development of narrow rifts, with application to continental rifts and passive margins, and, second, lithosphere spreading with application to the development of wide rifts and core complexes. Models of compression compare sandbox-type and brittle-ductile multilayer-type experiments. Results are applied to mountain belt formation and, in particular, to the Pyrenees and the western Alps. Both extensional and compressional experiments demonstrate that the presence/absence of a sub-Moho brittle mantle and the coupling/decoupling between brittle and ductile layers play a dominant role on localized versus distributed deformation, at lithosphere scale.