Faulting of the lithosphere during extension and related rift-flank uplift: a numerical study

Abstract

In this contribution, we present a new model of passive rifting and related rift-flank uplift. The numerical model is based on a lattice spring network coupled with a viscous particle model so that we can simulate visco-elasto-plastic behaviour with dynamic fault development. In our model, we show that rift-flank uplift can be achieved best when extension in the crust is localized and the lower crust is strong so that major rift faults transect the whole crust. Uplift of rift flanks follows a smooth function whereas down-throw in the rift basin takes place in steps. The geometry of the developing faults has also an influence on the uplift; in this case, displacement along major rift faults produces higher flanks than distributed displacement on many faults. Our model also shows that the relative elastic thickness of the crust has only a minor influence on the uplift since fault depth and elastic thickness are not independent. In addition, we show with a second set of simulations and analytically that a strain misfit between the upper and lower boundaries of a stretched crust, which is created by the horizontal extension, leads to an active uplift driven by elastic forces. We compare the numerical simulations, the analytical solution and real surface data from the Albertine rift in the East African Rift System and show that our new model can reproduce realistic features. Our two-layer beam model with strain misfit can also explain why a thick crust in the simulations can have an even higher rift flank than a thin crust even though the thin crust topography has a higher curvature. We discuss the implications of our simulations for real rift systems and for the current theory of rift-flank uplift.

The End of Midcontinent Rift Magmatism and the Paleogeography of Laurentia

“…Rift flank uplift is commonly associated with fault-driven subsidence, particularly that occurring in relatively narrow rift zones (Sachau and Koehn, 2010). As a result, there is a much higher potential for unconformities to be associated with intervals of active rifting rather than the broad thermal subsidence that follows.…”

Mountain-building under extension

“…We propose the hypothesis, that the Rwenzori block is uplifted by a mechanism that is based on similar principles as the uplift mechanism for rift flanks described in Sachau and Koehn (2010) and Sachau and others (2011).…”

“…In the east of the Rwenzoris, where they are still connected to the rift shoulders, seismicity extends from the surface down to 30 km depth. Brittle faulting seems to concentrate on the main boundary faults of the horst (Koehn and others, 2008;Ring, 2008;Sachau and Koehn, 2010), which is manifest in the location of the clustering of earthquake epicenters along the proposed major faults (Koehn and others, 2010;Lindenfeld and others, 2012). Seismic activity below 16 km depth outside the rift is almost nonexistent except for the area where the Rwenzori horst is connected to the Victoria plate (Lindenfeld and others, 2012), where a few extremely deep earthquakes have been measured.…”

A new mixed-mode fracture criterion for large-scale lattice models

“…Examples are models of crustal extension, which include the brittle ductile transition or materials with strong heterogeneities. We recalculated crustal-scale experiments with a brittle elastic crust from previous publications (Sachau and Koehn, 2010, 2012, and Sachau et al, 2013, with the same results as previously published.…”