Abstract
AbstractExtension of the continental lithosphere can lead to the formation of rifted margins with contrasting tectonic and geomorphologic characteristics. Many of these characteristics depend on the manner extension spatially distributed. Here we investigate the feedback between tectonics and the transfer of material at the surface resulting from erosion, transport, and sedimentation and discuss how they influence the rifting process. We use large‐scale (1,200×600 km), high‐resolution (1 km) numerical experiments coupling a 2‐D upper‐mantle‐scale thermo‐mechanical model with a planform 2‐D surface processes model. We test the sensitivity of the coupled models to varying crust‐lithospheric rheology and erosional efficiency. We confirm that the development and long‐term support of topography is dependent on the strength of the coupling between the crust and the mantle lithosphere. Strong coupling promotes high topography as the integrated strength of the lithosphere is sufficient to support the additional stress. Weak coupling results in the stress being relaxed via viscous flow in the middle/lower crust and leads to more subdued topography. Erosion and transport of sediment modulates this behavior but has only minor effect on the overall structure of the rift. High erosion efficiency counters the development of high topography and creates complex landscape morphologies while low erosion efficiency allows for longer standing high topography and results in more simple landscape morphologies. The transfer of mass between the continent and the basin alters the stress field at the onshore‐offshore transition and facilitates the development of faults, increasing their offsets and keeping them active over a longer period.
Highlights
The extension and subsequent breakup of the continental lithosphere is responsible for the formation of a wide range of rifted passive margins, with contrasting tectonic and geomorphological characteristics, ranging from the high-elevation cases characterized by sharp sub-aerial topography and prominent escarpments, to margins with low elevations with more subdued topography (e.g., Gallagher & Brown, 1997; Gilchrist & Summerfield, 1990) (Figure 1)
We investigate the feedback between tectonics and the transfer of material at the surface in the context of passive margin formation using 2-D thermo-mechanical models coupled to a state-of-the-art 2-D surface processes model
We present a series of forward numerical models coupling a large-scale two-dimensional thermomechanical model to a plane-view 2-D surface processes model
Summary
The extension and subsequent breakup of the continental lithosphere is responsible for the formation of a wide range of rifted passive margins, with contrasting tectonic and geomorphological characteristics, ranging from the high-elevation cases (south-eastern South Africa, Red Sea rift) characterized by sharp sub-aerial topography and prominent escarpments, to margins with low elevations (southern Australia, eastern Africa) with more subdued topography (e.g., Gallagher & Brown, 1997; Gilchrist & Summerfield, 1990) (Figure 1). A variety of mechanisms have been proposed to explain the existence of high-elevation topography onshore, including depth-dependent extension (e.g., Huismans & Beaumont, 2011, 2014), lateral heat flow (Steckler, 1981), induced asthenospheric convection (e.g., Huismans et al, 2001), plastic necking and flexural response to unloading (e.g., Braun & Beaumont, 1989), or magmatic underplating (e.g., McKenzie, 1984) These mechanisms can be invoked to explain a wide range of topographic wavelengths depending on the strength of the middle and lower crust which control the coupling between upper and lower parts of the lithosphere. It raises important questions on how the redistribution of mass by surface processes may affect the evolution of rifting
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