f Early Post-Rift Dynamo-Thermal Subsidence and Stratigraphic Architecture as Magma-Rich Rifted Margins Move off Plumes

Magma-rich rifting and breakup generally occur over rising mantle plumes; magma-poor rifting and breakup do not. Plumes generate up to 2km dynamic elevation at magma-rich rifts, outcompeting synrift subsidence in both active and ancient magma-rich margins, evidenced by top-rift unconformities. Magma-rich margins also show anomalously fast/large early post-rift subsidence, evidenced by thick, short-lived sag/salt sections with limited faulting. Syn-depositional thermal subsidence cannot be responsible for the rapid subsidence alone, and the paucity of faulting suggests it is not tectonic. Dissipation of dynamic topography (dynamic subsidence) is the additional parameter responsible, acting together with thermal subsidence. We depict the magma-rich central South Atlantic and Gulf of Mexico salt-bearing margins relative to former plumes, showing sag/salt deposition occurs as the margins migrate off plume flanks while rifting continues immediately over the plumes. However, the sub-sag/salt basement must first be extended/eroded during dynamic elevation to fall below its pre-uplift elevation. We propose new terms: "dynamo-thermal subsidence" creates "dynamo-thermal accommodation", the sum and combined result of dynamic plus thermal subsidence, respectively. It is fast enough to negate the need for deep, sub-sea level, subaerial depressions for accumulation of thick sag/salt sections. Differences in dynamic elevation during salt deposition also explains differences in autochthonous salt thickness.