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The Main Ethiopian Rift (MER) offers a complete record of the time-space evolution of a continental rift. We have characterized the brittle deformation in different rift sectors through the statistical analysis of a new database of faults obtained from the integration between satellite images and digital elevation models, and implemented with field controls. This analysis has been compared with the results of lithospheric-scale analogue models reproducing the kinematical conditions of orthogonal and oblique rifting. Integration of these approaches suggests substantial differences in fault architecture in the different rift sectors that in turn reflect an along-axis variation of the rift development and southward decrease in rift evolution. The northernmost MER sector is in a mature stage of incipient continental rupture, with deformation localised within the rift floor along discrete tectono-magmatic segments and almost inactive boundary faults. The central MER sector records a transitional stage in which migration of deformation from boundary faults to faults internal to the rift valley is in an incipient phase. The southernmost MER sector is instead in an early continental stage, with the largest part of deformation being accommodated by boundary faults and almost absent internal faults. The MER thus records along its axis the typical evolution of continental rifting, from fault-dominated rift morphology in the early stages of extension toward magma-dominated extension during break-up. The extrapolation of modelling results suggests that a variable rift obliquity contributes to the observed along-axis variations in rift architecture and evolutionary stage, being oblique rifting conditions controlling the MER evolution since its birth in the Late Miocene in relation to a constant post ca. 11 Mã N100°E Nubia-Somalia motion.

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The Main Ethiopian Rift (MER) is a narrow continental rift characterized by an along‐axis variation in rift evolution, with early stages in the south evolving to incipient breakup in the north. Although distribution and style of Quaternary volcanotectonic deformation is well known in the northern rift sector, knowledge of these characteristics is comparatively less constrained southward. In this paper we present the results of a field structural study carried out to better constrain the time‐space distribution of faulting in the central sector of the MER (central MER). The new field structural data coupled with new 14C radiometric dating of faulted rocks suggest a localization of faulting at both rift margins of the central MER, where radiometric dating of faulted material has allowed establishing a Late Pleistocene–Holocene activity of border faults. Conversely, in‐rift faulting (Wonji Fault Belt (WFB)) is subordinate highlighting a major difference with the northern sector of the MER where deformation is essentially accommodated in the axial zone. This is consistent with an along‐axis variation in rift evolution, showing the central MER less evolved than the northern rift sector. Inversion of cumulative fault slip data reveals a variation in the extension direction between the rift margins (N105°–110°E) and the rift floor (N90°–95°E), which accords well with the current Nubia‐Somalia plate kinematics. The variation in extension direction across the rift could manifest a slip partitioning between the boundary faults and in‐rift WFB faults.

[1] The Northern Apennines (NA) hinterland area is characterized by a complex Neogene-Quaternary tectonics where both crustal extension, associated with the Tyrrhenian Basin opening, and crustal shortening in the onshore area took part in the deformation. Analysis of synorogenic deposits preserved in the NNW trending Siena-Radicofani Basin (SRB), extending along a large part of the NA hinterland, documents the evolution of deformation of this sector during the last 9 Ma. Information from subsurface geology (deep seismic lines, commercial seismic lines, and deep wells), surface geology (mapping and structural analysis), and from analogue modeling was integrated and used to infer the tectono-sedimentary history of the SRB and its relation with structures in the substratum, as well as the possible implications for the evolution of the NA hinterland. The results we obtain indicate that the SRB and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation. Seismic lines across the SRB display various examples of compressional structures affecting the basin fill and the substratum, such as thrust anticlines and reverse faults. Notably, these basin-scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop-scale compressional structures. The thrust anticlines bounding the basins are often cored by Triassic evaporites (Burano Formation), suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution. In this circumstance, three series of scaled brittle-ductile physical models have been used to investigate the development of a basement cover system, with a décollement ductile layer at the base of the sedimentary cover. These models simulate the evolution of the Northern Apennines hinterland, where the basement is involved in the thrusting, and the sedimentary cover is shortened above a basal ductile layer given by the Burano Formation. Longitudinal models cross sections display similar deformation patterns to those observed in the NA hinterland, such as characteristic wavelength of both basement and cover structures, as well as detachment and fault propagation folding in the cover. Extensional tectonics is instead found to control sedimentation in the southern part of the SRB (at $8 Ma) or representing recent deformation. The older extensional event is here related to the forelandward propagation of Tyrrhenian-related extension that could reactivate suitably oriented basement thrusts.Transfer zones produced a differential propagation of extension, such that along-strike sectors of the hinterland were eventually deformed by different stress fields. Analysis of the SRB and of other adjoining basins reveals that the NA hinterland experienced alternated periods of forward and backward migration of the compression-extension transition. In our interpretation, the competition between extension and compression in the hinterland is relat...

The Rides Prerifaines (RP) of Morocco constitute the leading edge of the Rif chain. They involve a Triassic-Palaeocene succession deposited on a peneplained Palaeozoic fold belt and accumulated in basins delimited by NE-SW-trending normal fault systems. A significant hiatus separates an overlying Middle Miocene-Upper Miocene foredeep sequence. The reconstruction of the complex structural evolution of the RP during the later compressive phases that affected the Rif chain since Middle Miocene time has been the aim of this paper. We integrated field structural analyses, seismic line interpretation, and analogue modelling in order to evaluate the control exerted by the Late Triassic-Jurassic normal fault systems onto the later compressive tectonics. The maximum compression direction associated with the first compressive phase is roughly NE-SW to ENE-WSW oriented. During this phase the Mesozoic basin fill was scooped-out from the graben and the main décollement level were the Triassic evaporites. Since Pliocene times the maximum compression direction was oriented roughly N-S. During this phase the RP assumed their present structural setting. The earlier normal faults delimiting the Mesozoic graben were reactivated in a strike-slip mode also involving the Palaeozoic basement. The analogue modelling experiments demonstrated that the basement reactivation promoted salt tectonics and favoured fluid circulation.

We present an analysis of the distribution, timing, and characteristics of the volcano-tectonic activity on the western margin of the Southern Main Ethiopian Rift in the\ud Soddo area (latitudes between ~7°10'N and ~6°30'N). The margin is characterized by the presence of numerous normal faults, with limited vertical offset and often sigmoidal in shape, which accommodate a gentle transition from the rift floor to the Ethiopian plateau. New radiocarbon dating indicates post-30 ka fault activity, pointing to a significant Late Pleistocene-Holocene tectonic activity of the Soddo margin. Comparison of the fault architecture with analog models suggests that deformation has been controlled by a sub-E-W (roughly N100°E) extension direction, resulting in an oblique extension with respect to the roughly NE-SW-trending rift. This well accords with inversion of fault slip data collected on faults with Pleistocene-Holocene activity and is also in good agreement with recent GPS data from the Southern Main Ethiopian Rift. Our data support a close correlation between the recent volcanic activity and deformation in the study area, with eruptive vents located along the recent border faults; the axial tectono-magmatic activity is subordinate in the area. These findings support a transition from axial tectono-magmatic deformation in the Northern Main\ud Ethiopian Rift to marginal deformation in the Central and Southern Main Ethiopian Rift, in turn indicating an along-axis, north to south decrease in rift maturity