Major and Trace Element Compositions of Basaltic Lavas From Western Margin of Central Main Ethiopian Rift: Enriched Asthenosphere vs. Mantle Plume Contribution

2021 ◽  
Author(s):  
Daniel Meshesha ◽  
Takele Chekol ◽  
Sileshi Negussia
Keyword(s):  
Trace Element ◽  
Mantle Plume ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Western Margin ◽  
Basaltic Lavas

scholarly journals Distinguishing Plume and Metasomatized Lithospheric Mantle Contributions to Post-Flood Basalt Volcanism on the Southeastern Ethiopian Plateau

2019 ◽  
Vol 60 (5) ◽  
pp. 1063-1094 ◽  
Author(s):  
Wendy R Nelson ◽  
Barry B Hanan ◽  
David W Graham ◽  
Steven B Shirey ◽  
Gezahegn Yirgu ◽  
...  
Keyword(s):  
Trace Element ◽  
Mantle Plume ◽  
Upper Mantle ◽  
Lithospheric Mantle ◽  
Incompatible Trace Element ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Element Ratios ◽  
Ethiopian Plateau ◽  
Mafic Lavas

Abstract Magmatism in the East African Rift System (EARS) contains a spatial and temporal record of changing contributions from the Afar mantle plume, anciently metasomatized lithosphere, the upper mantle and the continental crust. A full understanding of this record requires characterizing volcanic products both within the rift valley and on its flanks. In this study, three suites of mafic, transitional to alkaline lavas, were collected over a northeast-southwest distance of ∼150 km along the southeastern Ethiopian Plateau, adjacent to the Main Ethiopian Rift. Specifically, late Oligocene to Quaternary mafic lavas were collected from Chiro, Debre Sahil and the Bale Mountains. New major element, trace element, 40Ar/39Ar ages and isotopic results (Sr, Nd, Pb, Hf, Os, He) show spatial and temporal variation in the lavas caused by dynamical changes in the source of volcanism during the evolution of the EARS. The trace element compositions of Oligocene and Miocene Chiro lavas indicate derivation from mildly depleted and nominally anhydrous lithospheric mantle, with variable inputs from the crust. Further south, Miocene Debre Sahil and alkaline Bale Mountains lavas have enriched incompatible trace element ratios (e.g. Ba/Nb = 12–43, La/SmN = 3·1–4·9, Tb/YbN = 1·6–2·4). Additionally, their 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf and 206Pb/204Pb values trend toward a radiogenic Pb (HIMU) component. Radiogenic 187Os/188Os in these lavas correlates positively with 206Pb/204Pb and trace element indicators consistent with ancient metasomatic enrichment of their mantle source. In contrast, transitional Miocene Bale Mountains lavas have lower incompatible trace element abundances, less enriched trace element ratios (Ba/Nb ∼7, La/SmN = 2·3–2·5) and less radiogenic isotopic signatures that originate from melting garnet-bearing, anhydrous lithospheric mantle (Tb/YbN = 2·5–2·9). Pliocene and Quaternary Bale Mountains basaltic lavas are chemically and isotopically similar to Main Ethiopian Rift lavas. Trace element and isotopic indicators in both of these suites denote an amphibole-bearing source distinct from that sampled by the older Bale Mountains lavas. Isotopically, Pliocene and Quaternary Bale lavas have notably less radiogenic Sr–Nd–Pb–Hf isotopic ratios. Quaternary Bale Mountains lavas have the strongest mantle plume contribution (3He/4He = 12·1–12·5 RA), while other Bale Mountains, Debre Sahil and Chiro lavas were derived dominantly by melting of lithospheric or upper mantle sources (3He/4He = 5·1–9·1 RA). A multi-stage, regional-scale model of metasomatism and partial melting accounts for the spatial and temporal variations on the southeastern Ethiopian Plateau. Early Debre Sahil and alkaline Bale Mountains mafic lavas are melts derived from Pan-African lithosphere containing amphibole-bearing metasomes, while later transitional Bale basalts are melts of lithosphere containing anhydrous, clinopyroxene-rich veins. These ancient metasomatized domains were eventually removed through preferential melting, potentially during thermal erosion of the lithosphere or lithospheric foundering. Pliocene and Quaternary Bale Mountains lavas erupted after tectonic extension progressed throughout Ethiopia and was accompanied by increased plume influence on the volcanic products.

Mantle flow and orography: the effect of basal lithospheric shearing and lateral erosion gradients on continental rifting

2021 ◽  
Author(s):  
Pietro Sternai
Keyword(s):  
Mantle Plume ◽  
Sedimentary Basins ◽  
Windward Side ◽  
Ethiopian Rift ◽  
Mantle Flow ◽  
Stream Power ◽  
Main Ethiopian Rift ◽  
Extensional Tectonic ◽  
Continental Rifts ◽  
Lateral Erosion

<p><span>Mantle plume-lithosphere interactions modulated by surface processes across extensional tectonic settings give rise to outstanding topographies and sedimentary basins. However, the nature of these interactions and the mechanisms through which they control the evolution of continental rifts are still elusive. Basal lithospheric shearing due to plume-related mantle flow leads to extensional lithospheric rupturing and associated magmatism, rock exhumation, and topographic uplift away from the plume axis by a distance inversely proportional to the lithospheric elastic thickness. When moisturized air encounters a topographic barrier, it rises, decompresses, and saturates, leading to enhanced erosion on the windward side of the uplifted terrain. Orographic precipitation and asymmetric erosional unloading facilitate strain localization and lithospheric rupturing on the wetter and more eroded side of an extensional system. This simple model is validated against petro-thermo-mechanical numerical experiments where a rheologically stratified lithosphere above a mantle plume is subject to fluvial erosion proportional to stream power during extension. These findings are consistent with Eocene mantle upwelling and flood basalts in Ethiopia synchronous with distal initiation of lithospheric stretching in the Red Sea and Gulf of Aden as well as asymmetric topography and slip along extensional structures where orography sets an erosional gradient in the Main Ethiopian Rift (MER). I conclude that, although inherently related to the lithosphere rheology, the evolution of continental rifts is even more seriously conditioned by the mantle and surface dynamics than previously thoughts.</span></p>

scholarly journals Quaternary volcano-tectonic activity in the Soddo region, western margin of the Southern Main Ethiopian Rift

Tectonics ◽  
2013 ◽  
pp. n/a-n/a ◽  
Author(s):  
Giacomo Corti ◽  
Federico Sani ◽  
Melody Philippon ◽  
Dimitrios Sokoutis ◽  
Ernst Willingshofer ◽  
...  
Keyword(s):  
Tectonic Activity ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift ◽  
Western Margin ◽  
Quaternary Volcano

Comparing slope stability analysis using limit equilibrium and finite elements simulations of deep-seated landslides along the western margin of the Main Ethiopian Rift

2021 ◽  
Author(s):  
Tesfay Kiros Mebrahtu ◽  
Thomas Heinze ◽  
Stefan Wohnlich
Keyword(s):  
Slope Stability ◽  
Factor Of Safety ◽  
Limit Equilibrium ◽  
Limit Equilibrium Method ◽  
Strength Reduction ◽  
Ethiopian Rift ◽  
Seismic Load ◽  
Main Ethiopian Rift ◽  
Western Margin ◽  
The Stability

<p>Landslides and ground failures are among the common geo-environmental hazards in many of the tectonically active hilly and mountainous terrains of Ethiopia, such as in the western margin of the Main Ethiopian Rift in Debre Sina area. Besides the geological preconditioning, bi-modal monsoon and seismic events in the tectonically highly active region are usually suspected triggers. In order to minimize the damage caused by the slope failure events, a detailed investigation of landslide-prone areas using numerical modelling plays a crucial role. The aim of this study is to assess the stability of slopes, to understand the relevant failure mechanisms, and to evaluate and compare safety factors calculated by the different available numerical methods. The stability was assessed for slopes of complex geometry and heterogeneous material using the limit equilibrium method and the shear strength reduction method based on finite elements. Furthermore, numerical analysis was done under static and pseudo-static loading using the horizontal seismic coefficient to model their stability during a seismic event. The slope stability analysis indicates that the studied slopes are unstable, and any small scale disturbance will further reduce the factor of safety and probably causing failure. The critical strength reduction factors from the finite element method are significantly lower than the factor of safety from the limit equilibrium method in all studied scenarios, such as Bishop, Janbu Simplified, Spencer and Morgenstern-Price. The difference is especially evident for heterogeneous slopes with joints, which often are initiation points for the failure planes. The simulations show that slope stability of landslide prone hills in the study area strongly depends on the saturation conditions and the seismic load. The studied slopes are initially close to failure and increased pore-pressure or seismic load are very likely triggers.</p>

scholarly journals Mixing and Crystal Scavenging in the Main Ethiopian Rift Revealed by Trace Element Systematics in Feldspars and Glasses

2019 ◽  
Vol 20 (1) ◽  
pp. 230-259 ◽  
Author(s):  
Fiona Iddon ◽  
Charlotte Jackson ◽  
William Hutchison ◽  
Karen Fontijn ◽  
David M. Pyle ◽  
...  
Keyword(s):  
Trace Element ◽  
Ethiopian Rift ◽  
Main Ethiopian Rift
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