Control of Pre‐rift Lithospheric Structure on the Architecture and Evolution of Continental Rifts: Insights From the Main Ethiopian Rift, East Africa

Abstract

We investigate the along‐axis variations in architecture, segmentation, and evolution of the Main Ethiopian Rift (MER), East Africa, and relate these characteristics to the regional geology, lithospheric structure, and surface processes. We first illustrate significant along‐axis variations in basin architecture through analysis of simplified geological cross sections in different rift sectors. We then integrate this information with a new analysis of Ethiopian topography and hydrography to illustrate how rift architecture (basin symmetry/asymmetry) is reflected in the margin topography and has been likely amplified by a positive feedback between tectonics (flexural uplift) and surface processes (fluvial erosion and unloading). This analysis shows that ~70% of the 500 km long MER is asymmetric, with most of the asymmetric rift sectors being characterized by a master fault system on the eastern margin. We finally relate rift architecture and segmentation to the regional geology and geophysical constraints on the lithosphere. We provide strong evidence that rift architecture is controlled by the contrasting nature of the lithosphere beneath the homogeneous, strong Somalian Plateau and the weaker, more heterogeneous Ethiopian Plateau, differences originating from the presence of pre‐rift zones of weakness on the Ethiopian Plateau and likely amplified by surface processes. The data provided by this integrated analysis suggest that asymmetric rifts may directly progress to focused axial tectonic‐magmatic activity, without transitioning into a symmetric rifting stage. These observations have important implications for the asymmetry of continental rifts and conjugate passive margins worldwide.

Perspectives on Continental Rifting Processes From Spatiotemporal Patterns of Faulting and Magmatism in the Rio Grande Rift, USA

“…Our estimated exhumation magnitudes and rates determined from thermal history modeling along with the localized patterns seen in Cenozoic magmatism further emphasizes the physiographic differences that exist between the southern, central, and northern RGR. Although a detailed exploration of crustal inheritance and regional preexisting structure is beyond the scope of this work, we propose that crustal and lithospheric properties (i.e., thickness and potentially age and rheology) control rift accommodation and play a role in the orientation of faulting and magmatism along the RGR, as seen in continental rifts elsewhere (Figure ; e.g., Brun, ; Corti, ; Fletcher et al, ; Corti et al, ; Corti et al, ). Therefore, we suggest that differences in rift accommodation mechanisms (i.e., faulting vs. magmatism) are likely controlled by deep‐seated lithospheric‐scale properties and architecture, rather than progressive stages of rift development (e.g., Corti, ).…”

Reconnaissance Basement Geology and Tectonics of South Zealandia

“…We suggest that the asymmetry in seafloor and Moho depth (both deepest on the south side of the trough Grobys et al, ), might also be suggestive of lithospheric control via the contrast between strong Median Batholith to the south and weak accretionary wedge to the north (cf. Bot et al, ; Corti et al, ) effectively guiding the rifting along the north edge of the batholith. The oblique orientation of this path (Figure ) is also mechanically favored (e.g., Heine & Brune, ).…”

The Geomorphology, Structure, and Lava Flow Dynamics of Peralkaline Rift Volcanoes From High‐Resolution Digital Elevation Models

“…Along‐axis variations in rifting stage may affect caldera architecture and the extent to which cross‐cutting structures influence their formation. The influence of such preexisting structures is likely larger in early stages of rifting than late stages (e.g., Corti, Molin, et al, ). This is arguably supported by the simpler geometry of Fentale's caldera in the northern MER (late stage rifting) compared to the geometry of Corbetti in the southern MER (earlier stage).…”