Evolution of rift systems and their fault networks in response to surface processes

During the formation of rifted continental margins, a rift evolves through a number of stages that produce major sedimentary basins and distinct rifted margin domains. While these domains have been classified based on the resulting structures and crustal thickness seen in geophysical data, the evolution of the fault network that produces these domains is not as well understood. Further, margin architecture may be influenced by erosion and sedimentation. Previous studies have qualitatively examined how faults respond to sedimentation during rifting, but there has not been a quantitative study on how variable surface processes efficiency affects fault network properties and the effect this has on rift evolution.

In this study we use a two-way coupling between the geodynamic code ASPECT (Kronbichler et al., 2012) and the surface processes code FastScape (Braun and Willett, 2013) to run 12 high-resolution 2D rift models that represent asymmetric, symmetric, and wide rift types (Neuharth et al., in review). For each rift type, we vary the surface process efficiency by altering the bedrock erodibility (K_f) from no surface processes to low (K_f = 10^-6 m^0.2/yr), medium (10^-5), and high efficiency (10^-4). To analyze these models, we use a novel quantitative fault analysis toolbox that extracts discrete faults from our continuum models and correlates them through space and time (https://github.com/thilowrona/fatbox). This toolbox allows us to track faults and their properties such as the number of faults, their displacement, and cumulative length, to see how they evolve through time, as well as how these properties change given different rifting types and surface processes efficiency.

Based on the evolution of fault network properties, we find that rift fault networks evolve through 5 major phases: 1) distributed deformation and coalescence, 2) fault system growth, 3) fault system decline and basinward localization, 4) rift migration, and 5) continental breakup. Each of these phases can be correlated to the rifted margin domains defined from geophysical data (e.g., proximal, necking, hyperextended, and oceanic). We find that surface processes do not have a large impact on the overall evolution of a rift, but they do affect fault network properties by enhancing strain localization, increasing fault longevity, and reducing the total length of a fault system. Through these changes, they can prolong rift phases and delay continental breakup with increasing surface process efficiency. To summarize, we find that surface processes do not change the overall evolution of rifts, but they do affect fault growth and as a result the timing of rifting.

 

Braun, J., and Willett, S.D., 2013, A very efficient O(n), implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution: Geomorphology, v. 180–181, p. 170–179, doi:10.1016/j.geomorph.2012.10.008.

Kronbichler, M., Heister, T., and Bangerth, W., 2012, High Accuracy Mantle Convection Simulation through Modern Numerical Methods.: Geophysical Journal International, v. 191, doi:doi:10.1111/j.1365-246x.2012.05609.x.

Neuharth, D., Brune, S., Wrona, T., Glerum, A., Braun, J., and Yuan, X.P., (in review at  Tectonics), Evolution of rift systems and their fault networks in response to surface processes, [preprint], doi: https://doi.org/10.31223/X5Q333