Crustal structure of the Main Ethiopian Rift from gravity data: 3-dimensional modeling

Mahatsente, R.; Jentzsch, G.; Jahr, T.

doi:10.1016/s0040-1951(99)00213-9

Cited by 92 publications

(93 citation statements)

References 22 publications

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“…Gravity analysis indicated the existence of a large magmatic intrusion at depth of 10 km beneath the Doguna volcano (Mahatsente et al, 1999), analogously to what was observed beneath the Wonji magmatic segments in the northern MER ( Fig. 1; Keranen et al, 2004).…”

Section: Volcano-tectonic Activitysupporting

confidence: 65%

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Minissale

Corti

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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In this study, the occurrence, chemical composition, origin and geothermal significance of thermal springs and fumaroles naturally discharging in the area located north of the Lake Abaya (western margin of the Main Ethiopian Rift, East Africa) are reviewed in relation with recent tectonics. All thermal springs showed a dominantly Na-HCO 3 composition, consistent with observations dating from at least 1972, and most of them displayed a narrow range of δD and δ 18 O isotopic compositions for water similar to regional meteoric origins. These observations suggest that water-rock interaction processes occur in all aquifers and dominate the contributions of water that actively circulate within thermal fluids, and also suggest a similar elevation of groundwater recharge throughout the study area. Most of the thermal springs are dominated by a CO 2 -rich gas phase and discharge along the active faults bordering the western edge of the Main Ethiopian Rift valley. The δ 13 C values of CO 2 and the 3 He/ 4 He isotopic ratios are consistent with the presence of mantle-derived fluids similar to what is observed in many other areas along the kinematically active African Rift, especially within Ethiopia. The application of geothermometric techniques in the liquid and the gas phases suggests the presence of a deep reservoir in which the fluids equilibrated at a maximum temperature of approximately 180°C. Additionally, the presence of fumaroles at boiling temperatures and water/mud boiling pools in several places suggests that the geothermal reservoir is positioned at a relatively shallow depth and likely located in the western side of the study area. The analysis of data collected throughout time reveals that the waters of Lake Abaya have experienced an increase in salinity of 20% paralleled contemporaneously with a decrease in pH and δ 18 O and δD of water in the last 40 years; these changes do not appear to be related to climate changeinduced increases in temperature or evaporation at the global scale.

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Section: Volcano-tectonic Activitysupporting

confidence: 65%

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Minissale

Corti

Tassi

et al. 2017

Journal of Volcanology and Geothermal Research

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“…To convert these pressures to based on gravity studies in the Main Ethiopian Rift (e.g. Mahatsente et al 1999). The calculated saturation depths are shallow: 0.2 to 1.4 km.…”

Section: Resultsmentioning

confidence: 99%

Integrated field, satellite and petrological observations of the November 2010 eruption of Erta Ale

et al. 2012

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Erta Ale volcano, Ethiopia, erupted in November 2010, emplacing new lava flows on the main crater floor, the first such eruption from the southern pit into the main crater since 1973, and the first eruption at this remote volcano in the modern satellite age. For many decades, Erta Ale has contained a persistently active lava lake which is ordinarily confined, several tens of metres below the level of the main crater, within the southern pit. We combine on-the-ground field observations with multispectral imaging from the SEV-IRI satellite to reconstruct the entire eruptive episode beginning on 11 November and ending prior to 14 December 2010. A period of quiescence occurred between 14 and 19 November. The main eruptive activity developed between 19 and 22 November, finally subsiding to pre-eruptive levels between 8 and 15 December. The estimated total volume of lava erupted is ∼0.006 km 3 . The mineralogy of the 2010 lava is plagioclase+clinopyroxene+olivine. Geochemically, the lava is slightly more mafic than previously erupted lava lining the caldera floor, but lies within the range of historical lavas from Erta Ale. SIMS analysis of olivine-hosted melt inclusions shows the Erta Ale lavas to be relatively volatile-poor, with H 2 O contents ≤1,300 ppm and CO 2 contents of ≤200 ppm. Incompatible trace and volatile element systematics of melt inclusions show, however, that the November 2010 lavas were volatile-saturated, and that degassing and crystallisation occurred concomitantly. Volatile saturation pressures are in the range 7-42 MPa, indicating shallow crystallisation. Calculated pre-eruption and melt inclusion entrapment temperatures from mineral/liquid thermometers are ∼1,150°C, consistent with previously published field measurements.

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“…The models show high P-wave velocities (6.5 km/s) beneath the axis of the rift at a depth of 12-25 km, consistent with the fi ndings of Keranen et al (2004), who found high P-wave velocities (6.5-6.8 km/s) at 7-15 km depth using tomographic inversion of the controlled-source traveltime data set. The presence of high V P /V S ratios (1.81-1.84) at 12-25 km, segmented positive Bouguer anomalies (Mahatsente, et al, 1999;Tiberi et al, 2005;Mickus et al, 2007), and coincidence with zones of surface Quaternary volcanism suggest that the higher-velocity, higher-density zones are cooled dense mafi c intrusions. The high V P /V S values, along with other geophysical evidence, suggest that magmatic processes continue to the present day.…”

Section: Crustal Tomographymentioning

confidence: 97%

“…In the following section, we present evidence to suggest that this melt source plays a vital role in the ongoing rifting process in Ethiopia. Regional long-wavelength trend from lowpass fi ltering (i.e., wavelengths more than ~80 km) of existing Ethiopian gravity data (e.g., Mahatsente et al, 1999;Tiberi et al, 2005). ( …”

Section: Bastow Et Almentioning

confidence: 99%

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

Bastow¹,

Keir²,

Daly³

2011

Volcanism and Evolution of the African Lithosphere

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The Miocene-Holocene East African Rift in Ethiopia is unique worldwide because it subaerially exposes the transition between continental rifting and seafl oor spreading within a young continental fl ood basalt province. As such, it is an ideal study locale for continental breakup processes and hotspot tectonism. Here, we review the results of a recent multidisciplinary, multi-institutional effort to understand geological processes in the region: The Ethiopia Afar Geoscientifi c Lithospheric Experiment (EAGLE). In 2001-2003, dense broadband seismological networks probed the structure of the upper mantle, while controlled-source wide-angle profi les illuminated both along-axis and across-rift crustal structure of the Main Ethiopian Rift. These seismic experiments, complemented by gravity and magnetotelluric surveys, provide important constraints on variations in rift structure, deformation mechanisms, and melt distribution prior to breakup. Quaternary magmatic zones at the surface within the rift are underlain by high-velocity, dense gabbroic intrusions that accommodate extension without marked crustal thinning. A magnetotelluric study illuminated partial melt in the Ethiopian crust, consistent with an overarching hypothesis of magmaassisted rifting. Mantle tomographic images reveal an ~500-km-wide low-velocity zone at ≥ ≥75 km depth in the upper mantle that extends from close to the eastern edge of the Main Ethiopian Rift westward beneath the uplifted and fl ood basaltcapped NW Ethiopian Plateau. The low-velocity zone does not interact simply with the Miocene-Holocene (rifting-related) base of lithosphere topography, but it also provides an abundant source of partially molten material that assists extension of the seismically and volcanically active Main Ethiopian Rift to the present day.

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Crustal structure of the Main Ethiopian Rift from gravity data: 3-dimensional modeling

Cited by 92 publications

References 22 publications

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Geothermal potential and origin of natural thermal fluids in the northern Lake Abaya area, Main Ethiopian Rift, East Africa

Integrated field, satellite and petrological observations of the November 2010 eruption of Erta Ale

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

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