Re‐orientation of the extension direction and pure extensional faulting at oblique rift margins: comparison between the Main Ethiopian Rift and laboratory experiments

Corti, Giacomo; Philippon, Mélody; Sani, Federico; Keir, Derek; Kidane, Tesfaye

doi:10.1111/ter.12049

Cited by 91 publications

(89 citation statements)

References 38 publications

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“…Thus, faults of two trends interacted within an oblique strain field relative to the divergence directions of the Nubian-and Somalian plates, finally resulting in rhomb-shaped tectonic patterns with both, dip-slip and strike-slip displacement. Minor counter-clockwise block rotations are required to accommodate the difference in slip direction along the different fault systems (Corti et al, 2013). This is supported by our palaeomagnetic data.…”

Section: Discussionsupporting

confidence: 68%

“…Kidane et al (2009) presented paleomagnetic results from a later rift stage in distinct regions within the MER, linking together volcanic segments of Quaternary age, which yielded about 7°counter-clockwise block rotations along vertical axis. This is consistent with a transtensional deformation process during Quaternary times in the Fentale region (Corti et al, 2013) and is also of relevance for the tectonics in our study area. Erosion and non-deposition affected some areas within the Ethiopian Rift in Quaternary times, which constitutes an important factor in the MGF´s stratigraphic record.…”

Section: ______________supporting

confidence: 72%

“…Galili (N 9,77°, E 040,55°) area is located in a central sector of the northernmost Main Ethiopian Rift (MER), that propagated north-eastwards into the southern Afar depression during Miocene to Pleistocene times (Hayward and Ebinger, 1996). Thereby, strain patterns changed their directions, and newly generated internal rift fault systems (Wonji faults) replaced marginal rift fault systems (Corti et al, 2013). Thus, Quaternary rift basins and magmatic segments ( Fig.…”

Section: Introductionmentioning

confidence: 99%

“…Ring, 2014;Corti et al, 2013), and especially as an area of early hominid evolution (e.g. Haile-Selassie et al, 2015;Kimbel and Delezene, 2009;Kullmer et al, 2008;Macchiarelli et al, 2004;Weber et al, 2001;White et al, 1993White et al, , 2006White et al, , 2009.…”

Section: Introductionmentioning

confidence: 99%

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Paleomagnetic constraints on stratigraphy and rift-related tectonics of Pliocene and Early Pleistocene volcano-sedimentary strata: the Mt. Galili hominid research area, Southern Afar Depression, Ethiopia

Popp¹,

Scholger²

2018

AJES

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Our paleomagnetic investigations in the Northern Main Ethiopian Rift concentrated on ascertaining characteristic remanence directions of volcanic and sedimentary layers embodied within the Mt.Galili Formation (MGF). Magnetic stratigraphy was applied mainly to support anthropological studies on early hominid evolution. The new paleomagnetic results provided implications for stratigraphic age determinations of the MGF, and they also support arguments for rift-related tectonics as block rotation and tilting relative to the stable African crust since the Pliocene.Based on 497 paleomagnetic samples, we applied magnetic stratigraphy on magmatic and sedimentary rocks to determine the 39age of the MGF and correlated the results with published Ar/ Ar age data on tuff and ignimbrite layers which range from ca. 5.4 Ma to ca. 2.3 Ma, consistent with biostratigraphic age constraints. Nine magnetic polarity intervals of the Gilbert zone were identified within the lower four members of the MGF covering a time span from 5.37 to 3.58 Ma. The upper two members of the MGF comprised three polarity intervals assigned to the upper Gauss and lower Matuyama polarity zones. In combination with an 39Ar/ Ar age of 2.35 Ma, located in the middle of the section, we infer that ca. 0.5 Ma and four polarity intervals are missing between the MGF's lower and upper members. We attribute this significant depositional gap to uplift of the region due to the intrusion of basalt magma, associated with deposition of the Upper Shabeley Laag Member.Extensional rift tectonic processes were intimately affiliated with magmatic activity and generation of rapidly changing sedimentary environments of the MGF`s deposits, but the bulk of the observed tectonic features resulted from post-depositional tectonic overprint, when the re-orientated Wonji Fault System affected the Mt.Galili area in the Quaternary period, thereby creating new internal rift (in older rift) structures. Tectonic movements of MGF`s strata were deduced from our analysed characteristic remanent magnetisation (ChRM) directions compared with Pliocene reference data. The investigation revealed almost unchanged orientation of the ChRM-directions for the marginal internal rift zone in the East of the Mt.Galili area, but moderate counterclockwise rotation for the central internal rift zone in the West. The North of the Mt.Galili area suffered moderate clockwise rotation, probably due to the Mt.Galili area`s regional position, adjoining a transfer zone between the Quaternary Angele and Addo-Do magmatic segments.

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Section: Discussionsupporting

confidence: 68%

Section: ______________supporting

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Paleomagnetic constraints on stratigraphy and rift-related tectonics of Pliocene and Early Pleistocene volcano-sedimentary strata: the Mt. Galili hominid research area, Southern Afar Depression, Ethiopia

Popp¹,

Scholger²

2018

AJES

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“…Throughout the MER, strain distribution has been documented by geodetic, geophysical and geological observations (Boccaletti et al, 1998;Bilham et al, 1999;Ebinger and Casey, 2001;Wolfenden et al, 2004;Keir et al, 2006;Corti et al, 2013), with extension primarily localised to a NNE trending,~30-km-wide rift axis known as the Wonji Fault Belt (WFB) (Mohr, 1967) (Fig. 1).…”

Section: Study Areamentioning

confidence: 99%

Spatial relationship between earthquakes and volcanic vents in the central-northern Main Ethiopian Rift

Mazzarini

Keir

Isola

2013

Journal of Volcanology and Geothermal Research

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During the breakup of continents extension is commonly accommodated by connected networks of fluid filled fractures (dykes) and by faults. Despite the importance of these two extension mechanisms their spatial relationship in three dimensions is poorly understood primarily because it is difficult to quantify the subsurface distribution of faulting and intrusion. In order to address this problem, we conduct a quantitative analysis of the spatial distribution and clustering of earthquakes and volcanic vents in the Main Ethiopian Rift in East Africa in order to understand how extension by faulting and intrusion is distributed throughout the volcanic rift. We use fractal analysis of earthquake epicentres in order to infer the 2D characteristics of the subsurface fault network, and directly test our model results against the 3D distribution of earthquake hypocentres. Our results show that fractal analysis of these features is a reliable means to characterise the 3D properties of the fault network. In addition, the strong similarity between the properties of the fault network derived from earthquakes and properties of the magma-filled fracture network derived from fractal analysis of volcanic vents strongly suggests that these are genetically linked. We then explore their spatial link using computation of earthquake and vent density, which shows that the zone of seismicity is generally around 20-30-km-wide, while the zone of vents is narrower and centred within the zone of seismicity. This spatial relationship suggests that the faults, which form rift axial grabens, are induced above a narrower and central zone of diking. We also demonstrate significant along-rift variation in degree of magmatism and faulting with regions of increased degree of diking inferred from a higher cone density characterised by reduced degree of faulting.

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Evolution, distribution, and characteristics of rifting in southern Ethiopia

et al. 2014

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Southern Ethiopia is a key region to understand the evolution of the East African rift system, since it is the area of interaction between the main Ethiopian rift (MER) and the Kenyan rift. However, geological data constraining rift evolution in this remote area are still relatively sparse. In this study the timing, distribution, and style of rifting in southern Ethiopia are constrained by new structural, geochronological, and geomorphological data. The border faults in the area are roughly parallel to preexisting basement fabrics and are progressively more oblique with respect to the regional Nubia-Somalia motion proceeding southward. Kinematic indicators along these faults are mainly dip slip, pointing to a progressive rotation of the computed direction of extension toward the south. Radiocarbon data indicate post 30 ka faulting at both western and eastern margins of the MER with limited axial deformation. Similarly, geomorphological data suggest recent fault activity along the western margins of the basins composing the Gofa Province and in the Chew Bahir basin. This supports that interaction between the MER and the Kenyan rift in southern Ethiopia occurs in a 200 km wide zone of ongoing deformation. Fault-related exhumation at~10-12 Ma in the Gofa Province, as constrained by new apatite fission track data, occurred later than the~20 Ma basement exhumation of the Chew Bahir basin, thus pointing to a northward propagation of the Kenyan rift-related extension in the area.

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Re‐orientation of the extension direction and pure extensional faulting at oblique rift margins: comparison between the Main Ethiopian Rift and laboratory experiments

Cited by 91 publications

References 38 publications

Paleomagnetic constraints on stratigraphy and rift-related tectonics of Pliocene and Early Pleistocene volcano-sedimentary strata: the Mt. Galili hominid research area, Southern Afar Depression, Ethiopia

Paleomagnetic constraints on stratigraphy and rift-related tectonics of Pliocene and Early Pleistocene volcano-sedimentary strata: the Mt. Galili hominid research area, Southern Afar Depression, Ethiopia

Spatial relationship between earthquakes and volcanic vents in the central-northern Main Ethiopian Rift

Evolution, distribution, and characteristics of rifting in southern Ethiopia

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