Basin Inversion Along Passive Margins: Insights From 2/3-D Numerical Modelling

Abstract

Recent seismic studies showing long-wavelength, shallow angle unconformities and broad low-amplitude anticlines in rift basins demonstrate that continuous post-rift compression along passive margins is relatively common, even between episodes of far-field plate-boundary changes (Holford et. al., 2014). Understanding the cause and timing of inversions in sedimentary rift basins along passive margins is critical for hydrocarbon exploration, given their role as structural traps. The cause of inversion in many basins has generally been attributed to first-order plate boundary changes, ridge-push forces and mantle dynamics. Previous studies have suggested that the rift-push force, caused by the buoyant upwelling asthenosphere beneath a rift is sufficiently strong to match the magnitude of far-field tectonic forces during rifting and break-off (Davis and Kusznir, 2002; Huismans et. al., 2001). It is therefore possible that the interaction of far-field tectonic and buoyant forces on a rifting margin is able to produce long-term, spatially localised patterns of compression, despite constant divergent plate motion. To test this, we used a 2/3D self-consistent thermo-mechanical numerical finite element code: Underworld. Underworld is capable of modelling high-resolution lithospheric systems with complex non-linear temperature, stress, strain, strain-rate dependent visco-plastic rheologies. Radiogenic heating, partial melting, and surface processes, are also incorporated into the model. A suite of experiments using a generic model of continental lithosphere allowed us to explore a range of extension velocities, sedimentations, and rheologies. Buoyancy forces were isolated by restarting experiments at set amounts of extension with the kinematic boundary conditions removed. The experimental results show that in both two and three dimensions, sedimentary basins along the rifted margins display temporally and spatially variable patterns of extension and compression, of similar magnitude (~20 MPa compressive stress) and scale (~100 km wavelength) to that described in nature. These results indicate that buoyancy forces play an important role in contractional re-activation of passive margin and basin inversion.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015