Search

Salt‐bearing rifted margins comprise some of the most structurally complex and economically important sedimentary basin settings such as the South Atlantic and the Gulf of Mexico salt basins. They are also involved with some of the largest uncertainties regarding the crustal and syn‐rift basin architecture and supra‐salt tectonic evolution, as well as the link between rifted margin architecture with salt deposition and post‐rift gravity‐driven salt tectonics. We thus conduct a margin‐scale study along nearly the entire West African salt basin, from South Gabon to Namibe, combining a vast data set of 2D and 3D seismic and well data with gravimetric and magnetic data to analyse its along‐strike rift and salt tectonic structural variability. We construct regional structural and thickness maps of key salt and post‐salt intervals to depict the history of individual margin segments and to investigate (1) how rifting and rifted margin architecture influences post‐rift salt tectonics evolution, (2) how these vary through time and space and (3) what are the controls between their different salt tectonic styles. We show that rifting and rift structures controlled the salt basin geometry, thickness and base‐salt relief in different ways for the different margin segments, and drastically influenced their post‐rift salt tectonic evolution. Differences in post‐salt sediment supply and continental uplift also had a role in their salt tectonic evolution. The results also have general implications to understand the interplay between rifted margin architecture with post‐rift salt tectonics for salt‐bearing rifted margins. [ABSTRACT FROM AUTHOR]

The Iberian-Newfoundland Margins have commonly been used as analogues to describe rifted margins. The Iberian margin is well constrained thanks to the DSDP-IODP wells, seismic reflection and refraction datasets. Considerable similarities are also observed within the world-class field analogues in the Swiss Alps. The resultant so called "Iberian model" can satisfyingly be applied to several cases of margins where mantle is exhumed by detachment faulting, often associated with syn-rift sediment-starved environment (Somalia, East India). However, these features do not necessarily reflect the actual diversity of margins worldwide, and may rather correspond to an end-member model.Recent observations reveal that some margins are characterized by a continental crust that exhibits macro-ductile behavior with strong internal shear and core-complex geometries up to the final break-up which demonstrates a different kind of margin evolution. Thermomechanical numerical models suggest that this deformation is the consequence of a weak rheological behavior of the crust modeled using a thick ductile lower crust. At the foot of these weak margins, either magma-rich or magma-poor, crustal shear zones are commonly observed as the main accommodating structures for hyper-extension. They consist of large-scale low-angle normal faults in the upper crust rooting on horizontal shears in the lower crust. The deformation pattern can be either basin-ward with a migration of the deformation and associated sedimentation/volcanic activity or more diffuse and chaotic. In some cases, low-angle shear zones define an anastomosed pattern that delineates boudin-like structures inside the crust up to the basement-sediment interface. In the upper brittle crust, the maximum deformation is localized in the inter-boudin areas where lower crustal material is commonly exhumed by low-angle shear-zones (core-complexes). These observations consistently indicate an enhanced ductile behavior of crustal rocks compared to the Iberian archetypal case of margin where the brittle deformation is more expressed and normal faults couple very early in the deformation history to the mantle. This ability to couple to the mantle can also be observed in the magma-poor end member of weak margins (e.g. Gabon margin) but strongly delayed in the deformation history. We argue that a mechanically-decoupled continental crust prevents surface faults from reaching mantle rocks, delaying a proper continental rupture. This delay might be due to the fact that the upper brittle crust is the strongest layer of the continental lithosphere ("crème-brulée" rheological behavior) in the contrary to the Iberian-type margins where the upper mantle is the strongest layer of the lithosphere. Considering the tectonic and sedimentary contexts of these "wide" margins, a likely interpretation is that the thinning of the crust is triggered by a hot thermal regime (inherited or acquired).We present and discuss a set of archetypal seismic profiles and propose a simple classification of passive margins based on the magmatic input and the rheology of the continental crust during rifting. We also discuss the parameters (structural inheritage, thermal evolution, mantle fertility, sedimentary input, magmatic history...) that might drive the development of a margin toward a weak or strong pole or a magma-rich or –poor pole. [ABSTRACT FROM AUTHOR]