Factors controlling early stage salt tectonics at rifted continental margins and their thermal consequences

Abstract

We use 2-D thermomechanical models to investigate the early evolution of rifted margin salt tectonics in terms of the competition among margin tilt, salt flow, and sediment aggradation. Model experiments include initial geometry of the rifted margin and autochthonous salt basin, subsequent synrift and thermal subsidence, sediment and water loading, and sediment compaction. We also calculate the thermal evolution of the system to investigate the impact of the high thermal conductivity of the salt (halite). Model Set 1 demonstrates a two-phase response to salt deposition: short-term thermal equilibration between the salt and crust and longer-term relaxation in which the salt basin thermal image penetrates to a depth on the order of its width. Set 2 addresses the competition among margin tilt, salt flow, and sediment aggradation. Set 3 examines other factors, the salt basin width and depth, and the rifted margin width, which potentially affect the system evolution. Set 4 shows that sawtooth subsalt topography, representing faulted basement grabens, does not strongly impede salt flow. The model results are discussed in terms of a ternary diagram with apices representing tilt, salt flow, and sedimentation rates. Characteristic styles include the following: (1) tilt and rapid salt flow draining salt to the distal basin before the sediment aggrades, (2) an equivalent system with faster aggradation that captures draining salt as diapirs between minibasins, and (3) rapid sediment aggradation in which diapir-minibasins systems develop before the salt drains. Thermal consequences of these styles are discussed. A preliminary comparison shows that salt structures resembling these styles occur in the southwest Nova Scotian margin. Key Points Margin tilt, salt flow and sediment aggradation controls salt basins Rifted margin salt basins can perturb thermal structure of the lithosphere Salt mobility affects thermal history of rifted margin sedimentary basins ©2013. American Geophysical Union. All Rights Reserved.