The Afar Depression: transition between continental rifting and sea-floor spreading

Makris, J.; Ginzburg, A.

doi:10.1016/0040-1951(87)90186-7

Cited by 214 publications

(299 citation statements)

References 8 publications

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“…Using a crustal density of 2780 kg m −3 (Makris and Ginzburg 1987), we calculate that most melt inclusions were trapped at 5-10 km depth (consistent with seismic data for the depth of a magma body; Hamlyn et al 2014), but some may have been trapped close to the base of the crust, around 20 km depth . The magma storage region is most likely composed of a series of sills and old eruptive products, evidenced by the presence of xenocrystic material in the magmas.…”

Section: Magma Storage Depths and Plumbing System At Nabrosupporting

confidence: 63%

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

Donovan

Blundy

Oppenheimer

et al. 2017

Contrib Mineral Petrol

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The 2011 eruption of Nabro volcano, Eritrea, produced one of the largest volcanic sulphur inputs to the atmosphere since the 1991 eruption of Mt. Pinatubo, yet has received comparatively little scientific attention. Nabro forms part of an off-axis alignment, broadly perpendicular to the Afar Rift, and has a history of large-magnitude explosive silicic eruptions, as well as smaller more mafic ones. Here, we present and analyse extensive petrological data obtained from samples of trachybasaltic tephra erupted during the 2011 eruption to assess the pre-eruptive magma storage system and explain the large sulphur emission. We show that the eruption involved two texturally distinct batches of magma, one of which was more primitive and richer in sulphur than the other, which was higher in water (up to 2.5 wt%). Modelling of the degassing and crystallisation histories demonstrates that the more primitive magma rose rapidly from depth and experienced degassing crystallisation, while the other experienced isobaric cooling in the crust at around 5 km depth. Interaction between the two batches occurred shortly before the eruption. The eruption itself was likely triggered by recharge-induced destabilisation of vertically extensive mush zone under the volcano. This could potentially account for the large volume of sulphur released. Some of the melt inclusions are volatile undersaturated, and suggest that the original water content of the magma was around 1.3 wt%, which is relatively high for an intraplate setting, but consistent with seismic studies of the Afar plume. This eruption was smaller than some geological eruptions at Nabro, but provides important insights into the plumbing systems and dynamics of off-axis volcanoes in Afar.

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Section: Magma Storage Depths and Plumbing System At Nabrosupporting

confidence: 63%

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

Donovan

Blundy

Oppenheimer

et al. 2017

Contrib Mineral Petrol

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“…Uppermost mantle Pn velocities from wide-angle seismic (e.g., Berckhemer et al, 1975;Makris and Ginzburg, 1987) and local earthquake data (Stork et al, in review) are as low as 7.2 km/s beneath Afar -markedly low compared to the global mean and compared to extensional settings with similar rates of opening (Fig. 6).…”

Section: Evidence From Broadband Seismologymentioning

confidence: 96%

“…Discussion has often focussed on whether the crust is completely new oceanic crust, or whether it is stretched and thinned continental crust, heavily intruded by magma (transitional crust). Constraints on crustal structure primarily come from wide-angle seismic studies (Berckhemer et al, 1975;Maguire et al, 2006;Makris and Ginzburg, 1987;Prodehl et al, 1997), teleseismic receiver function studies (Ayele et al, 2004;Dugda et al, 2005;Hammond et al, 2011;Stuart et al, 2006), and from gravity analysis (Redfield et al, 2003;Tessema and Antoine, 2004;Tiberi et al, 2005). Results achieved using these different methods are broadly consistent (e.g., Fishwick and Bastow, 2011).…”

Section: Crustal Structurementioning

confidence: 99%

“…The structure and composition of the crust beneath Afar have been the subject of much debate during the last~35 years (e.g., Berckhemer et al, 1975;Hammond et al, 2011;Makris and Ginzburg, 1987;Mohr, 1970Mohr, , 1989. Discussion has often focussed on whether the crust is completely new oceanic crust, or whether it is stretched and thinned continental crust, heavily intruded by magma (transitional crust).…”

Section: Crustal Structurementioning

confidence: 99%

“…Study of the rift system in Ethiopia is particularly useful because it exposes Tectonophysics 607 (2013) [98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114] subaerially several stages of magmatically active rift sector development from immature continental rifting in the East African rift to incipient oceanic spreading in the Red Sea and Gulf of Aden (e.g., Hayward and Ebinger, 1996;Makris and Ginzburg, 1987;Mohr, 1967) (Fig. 1).…”

Section: Introductionmentioning

confidence: 99%

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The development of extension and magmatism in the Red Sea rift of Afar

et al. 2013

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Despite the importance of continental breakup in plate tectonics, precisely how extensional processes such as brittle faulting, ductile plate stretching, and magma intrusion evolve in space and time during the development of new ocean basins remains poorly understood. The rifting of Arabia from Africa in the Afar depression is an ideal natural laboratory to address this problem since the region exposes subaerially the tectonically active transition from continental rifting to incipient seafloor spreading. We review recent constraints on along-axis variations in rift morphology, crustal and mantle structure, the distribution and style of ongoing faulting, subsurface magmatism and surface volcanism in the Red Sea rift of Afar to understand processes ultimately responsible for the formation of magmatic rifted continental margins. Our synthesis shows that there is a fundamental change in rift morphology from central Afar northward into the Danakil depression, spatially coincident with marked thinning of the crust, an increase in the volume of young basalt flows, and subsidence of the land towards and below sea-level. The variations can be attributed to a northward increase in proportion of extension by ductile plate stretching at the expense of magma intrusion. This is likely in response to a longer history of localised heating and weakening in a narrower rift. Thus, although magma intrusion accommodates strain for a protracted period during rift development, the final stages of breakup are dominated by a phase of plate stretching with a shift from intrusive to extrusive magmatism. This late-stage pulse of decompression melting due to plate thinning may be responsible for the formation of seaward dipping reflector sequences of basalts and sediments, which are ubiquitous at magmatic rifted margins worldwide.

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Differentiating flow, melt, or fossil seismic anisotropy beneath Ethiopia

Hammond¹,

Kendall

Wookey

et al. 2014

Geochem Geophys Geosyst

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Ethiopia is a region where continental rifting gives way to oceanic spreading. Yet the role that pre-existing lithospheric structure, melt, mantle flow, or active upwellings may play in this process is debated. Measurements of seismic anisotropy are often used to attempt to understand the contribution that these mechanisms may play. In this study, we use new data in Afar, Ethiopia along with legacy data across Ethiopia, Djibouti, and Yemen to obtain estimates of mantle anisotropy using SKS-wave splitting. We show that two layers of anisotropy exist, and we directly invert for these. We show that fossil anisotropy with fast directions oriented northeast-southwest may be preserved in the lithosphere away from the rift. Beneath the Main Ethiopian Rift and parts of Afar, anisotropy due to shear segregated melt along sharp changes in lithospheric thickness dominates the shear-wave splitting signal in the mantle. Beneath Afar, away from regions with significant lithospheric topography, melt pockets associated with the crustal and uppermost mantle magma storage dominate the signal in localized regions. In general, little anisotropy is seen in the uppermost mantle beneath Afar suggesting melt retains no preferential alignment. These results show the important role melt plays in weakening the lithosphere and imply that as rifting evolves passive upwelling sustains extension. A dominant northeast-southwest anisotropic fast direction is observed in a deeper layer across all of Ethiopia. This suggests that a conduit like plume is lacking beneath Afar today, rather a broad flow from the southwest dominates flow in the upper mantle.

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The Afar Depression: transition between continental rifting and sea-floor spreading

Cited by 214 publications

References 8 publications

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

The 2011 eruption of Nabro volcano, Eritrea: perspectives on magmatic processes from melt inclusions

The development of extension and magmatism in the Red Sea rift of Afar

Differentiating flow, melt, or fossil seismic anisotropy beneath Ethiopia

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