Architecture of Continental Rifts with Special Reference to East Africa

Rosendahl, Bruce R.

doi:10.1146/annurev.ea.15.050187.002305

Cited by 752 publications

(233 citation statements)

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“…The seismically and volcanically active EARS extends several thousands of kilometres and accommodates extension between the Nubian (African) and Somalian plates (Rosendahl, 1987;Braile et al, 1995;Chorowicz, 2005). At the northern end of the EARS, the volcanically active Main Ethiopian Rift (MER) records the transition from continental rifting to seafloor spreading in the Red Sea and Gulf of Aden (Hayward and Ebinger, 1996;Ebinger and Casey, 2001;Bonini et al, 2005;Corti, 2009;Agostini et al, 2011a).…”

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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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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“…However, Lakes Malawi, Tanganyika, and Bosumtwi are positioned in topographically low areas and are underlain by comparatively impervious Proterozoic crystalline rocks; hydrological modeling studies indicate negligible ground water outflow (29)(30)(31). Lakes Malawi and Tanganyika extend along Ͼ1,500 km of the western branch of the East African Rift, across seven discrete, independently deforming structural basins (42). Our lake levels records show coincident behavior in Lakes Malawi, Tanganyika, and Bosumtwi, and accordingly those shifts are driven by regional changes in the evaporation-precipitation balance in tropical Africa, and not by tectonic activity or deformation-enhanced ground water seepage.…”

Section: (Si Text)mentioning

confidence: 99%

East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins

Scholz

Johnson

Cohen

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

399

327

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The environmental backdrop to the evolution and spread of early Homo sapiens in East Africa is known mainly from isolated outcrops and distant marine sediment cores. Here we present results from new scientific drill cores from Lake Malawi, the first long and continuous, high-fidelity records of tropical climate change from the continent itself. Our record shows periods of severe aridity between 135 and 75 thousand years (kyr) ago, when the lake's water volume was reduced by at least 95%. Surprisingly, these intervals of pronounced tropical African aridity in the early latePleistocene were much more severe than the Last Glacial Maximum (LGM), the period previously recognized as one of the most arid of the Quaternary. From these cores and from records from Lakes Tanganyika (East Africa) and Bosumtwi (West Africa), we document a major rise in water levels and a shift to more humid conditions over much of tropical Africa after Ϸ70 kyr ago. This transition to wetter, more stable conditions coincides with diminished orbital eccentricity, and a reduction in precession-dominated climatic extremes. The observed climate mode switch to decreased environmental variability is consistent with terrestrial and marine records from in and around tropical Africa, but our records provide evidence for dramatically wetter conditions after 70 kyr ago. Such climate change may have stimulated the expansion and migrations of early modern human populations.human origins ͉ Lake Malawi ͉ paleoclimate ͉ Pleistocene

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“…This diversity mirrors that of continental rifts from which rifted margins develop (Rosendahl 1987;Sengör and Burke 1978).…”

Section: Introductionmentioning

confidence: 82%

“…Some continental rifts develop by stretching and thinning of diverging continental edges with a negligible amount of pre-or syn-rift magmatism, for example, the western branch of the East African Rift (Ebinger 1989;Rosendahl 1987). In some cases continued divergence results in extreme attenuation of crustal lithologies and even exposure of mantle rocks prior to the onset of seafloor spreading (Peron-Pinvidic et al 2013).…”

Section: Volcanic Rifted Marginsmentioning

confidence: 99%

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

Karson

2016

Can. J. Earth Sci.

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Rifting near hotspots results in mantle melting to create thick mafic igneous crust at volcanic rifted margins (VRMs). This mafic crust is transitional between rifted continental crust with mafic intrusions landward and oceanic crust into which it grades seaward. Seismic velocities, crustal drilling, and exhumed margins show that the upper crust in these areas is composed of basaltic lava erupted in subaerial to submarine conditions intruded by downward increasing proportions of dikes and sparse gabbroic intrusions. The lower crust of these regions is not exposed but is inferred from seismic velocities (Vp > 6.5 km/sec) and petrological constraints to be gabbroic to ultramafic in composition. Limited access to crustal sections generated along VRMs have raised questions regarding the composition and structure of this transitional crust and how it evolves during the early stages of rifting and subsequent seafloor spreading. Active processes in Iceland provide a glimpse of subaerial spreading with the creation of a thick (40-25 km) mafic igneous crust that may be analogous to the transitional crust of VRMs. Segmented rift zones that propagate away from the Iceland hotspot, migrating transform fault zones, and rift-parallel strike-slip faults create a complex plate boundary zone in the upper, brittle crust. These structures may be decoupled from underlying lower crustal gabbroic rocks that are capable of along-axis flow that smooths-out crustal thickness variations. Similar processes may be characteristic of the early history of VRMs and volcanic hotspot ridges related to rifting and seafloor spreading proximal to hotspots. Résumé :De la distension à proximité de points chauds génère une fusion du manteau créant une épaisse croûte ignée mafique aux marges de divergence des volcans (VRM). Cette croûte mafique constitue une transition entre la croûte continentale de divergence comportant des intrusions mafiques du côté continental et la croûte océanique dans laquelle elle s'intègre vers le large. Les vitesses sismiques, les forages dans la croûte et les bordures exhumées montrent que, dans ces secteurs, la croûte supérieure est composée de lave basaltique ayant fait éruption sous des conditions subaériennes à sous-marines et elle a été pénétrée par des intrusions gabbroïques éparses et des dykes dont les proportions augmentent vers le bas. La croûte inférieure de ces régions n'affleure pas mais selon les vitesses sismiques (Vp > 6,5 km/sec) et les contraintes pétrologiques elle serait de composition gabbroïque à ultramafique. L'accès limité aux sections de la croûte générées le long des VRM a soulevé des questions quant à la composition et la structure de cette croûte de transition et de son évolution durant les premiers stades de distension et d'étalement subséquent du plancher océanique. Des processus actifs en Islande fournissent un aperçu de l'étalement subaérien avec la création d'une épaisse (40-25 km) croûte ignée mafique qui pourrait être analogue à la croûte de transition des VRM. Des zones de rift ...

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Architecture of Continental Rifts with Special Reference to East Africa

Cited by 752 publications

References 0 publications

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

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

East African megadroughts between 135 and 75 thousand years ago and bearing on early-modern human origins

Crustal accretion of thick mafic crust in Iceland: implications for volcanic rifted margins

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