Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia

Rampey, Michael L.; Oppenheimer, Clive; Pyle, David M.; Yirgu, Gezahegn

doi:10.1016/j.jafrearsci.2014.04.009

Cited by 10 publications

(8 citation statements)

References 30 publications

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“…In contrast, there are few data available for Kone volcano. Cole (1969) and Rampey et al (2010) provide descriptions of major map units; however, previous petrographic and geochemical investigations have largely been limited to a Plinian eruptive deposit known as the Gubisa formation ( Figure 1d; Rampey et al, 2014), with some limited data also available on basalts that infill the caldera structure (Furman, 2007;Rooney et al, 2007;Rooney, Hanan, 2012).…”

Section: 1029/2018gc007836mentioning

confidence: 99%

“…The Kone central volcanic complex comprises the older ~95 km 2 caldera (Birenti), and the younger, 22 km 2 Kone caldera with a small embayment of 2 km 2 known as the Korke caldera (Rampey et al, , ; Figure d). Both structures are thought to have formed during a multieruption event, with the later Kone and Korke calderas developing during a series of three to four sub‐Plinian and Plinian eruptions (Rampey et al, , ). The Gubisa formation is associated with the formation of the Kone caldera (Figure d); deposits are up to 60 m thick with a minimum volume of 3.2 km 3 (Rampey et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

“…Both structures are thought to have formed during a multieruption event, with the later Kone and Korke calderas developing during a series of three to four sub‐Plinian and Plinian eruptions (Rampey et al, , ). The Gubisa formation is associated with the formation of the Kone caldera (Figure d); deposits are up to 60 m thick with a minimum volume of 3.2 km 3 (Rampey et al, ). Deposits associated with caldera‐forming events are well preserved and dominate surface exposure at the Kone volcanic complex.…”

Section: Geological Settingmentioning

confidence: 99%

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

Iddon

Jackson

Hutchison

et al. 2019

Geochem Geophys Geosyst

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For many magmatic systems, crystal compositions preserve a complex and protracted history, which may be largely decoupled from their carrier melts. The crystal cargo may hold clues to the physical distribution of melt and crystals in a magma reservoir and how magmas are assembled prior to eruptions. Here we present a geochemical study of a suite of samples from three peralkaline volcanoes in the Main Ethiopian Rift. While whole‐rock data show strong fractional crystallization signatures, the trace element systematics of feldspars, and their relationship to their host glasses, reveals complexity. Alkali feldspars, particularly those erupted during caldera‐forming episodes, have variable Ba concentrations, extending to high values that are not in equilibrium with the carrier liquids. Some of the feldspars are antecrysts, which we suggest are scavenged from a crystal‐rich mush. The antecrysts crystallized from a Ba‐enriched (more primitive) melt, before later entrainment into a Ba‐depleted residual liquid. Crystal‐melt segregation can occur on fast timescales in these magma reservoirs, owing to the low‐viscosity nature of peralkaline liquids. The separation of enough residual melt to feed a crystal‐poor postcaldera rhyolitic eruption may take as little as months to tens of years (much shorter than typical repose periods of 300–400 years). Our observations are consistent with these magmatic systems spending significant portions of their life cycle dominated by crystalline mushes containing ephemeral, small (< 1 km3) segregations of melt. This interpretation helps to reconcile observations of high crustal electrical resistivity beneath Aluto, despite seismicity and ground deformation consistent with a magma body.

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Section: 1029/2018gc007836mentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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

Iddon

Jackson

Hutchison

et al. 2019

Geochem Geophys Geosyst

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“…12) lacks a detailed time frame for the initiation of faulting, volcanic edifice development, and caldera formation. Further work from both surface geology and deep wells will be needed to build a detailed chronostratigraphy, and link caldera formation with the eruptive deposits (e.g., Rampey et al, 2014). Elliptical calderas appear to be a ubiquitous feature of the MER and continental rift systems in general (Acocella et al, 2003;Bosworth et al, 2003;Geyer and Marti, 2008), and whether these elongations are related to regional stress or preexisting structures remains uncertain.…”

Section: Conclusion and Future Opportunitiesmentioning

confidence: 99%

Structural controls on fluid pathways in an active rift system: A case study of the Aluto volcanic complex

et al. 2015

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In volcanically and seismically active rift systems, preexisting faults may control the rise and eruption of magma, and direct the flow of hydrothermal fluids and gas in the subsurface. Using high-resolution airborne imagery, field observations, and CO 2 degassing data on Aluto, a typical young silicic volcano in the Main Ethiopian Rift, we explore how preexisting tectonic and volcanic structures control fluid pathways and spatial patterns of volcanism, hydrothermal alteration and degassing. A new light detection and ranging (lidar) digital elevation model and evidence from deep geothermal wells show that the Aluto volcanic complex is dissected by rift-related extensional faults with throws of 50-100 m. Mapping of volcanic vent distributions reveals a structural control by either rift-aligned faults or an elliptical caldera ring fracture. Soil-gas CO 2 degassing surveys show elevated fluxes (>>100 g m -2 d -1 ) along major faults and volcanic structures, but significant variations in CO 2 flux along the fault zones reflect differences in near-surface permeability caused by changes in topography and surface lithology. The CO 2 emission from an active geothermal area adjacent to the major fault scarp of Aluto amounted to ~60 t d -1 ; we estimate the total CO 2 emission from Aluto to be 250-500 t d -1 . Preexisting vol canic and tectonic structures have played a key role in the development of the Aluto volcanic complex and continue to facilitate the expulsion of gases and geothermal fluids. This case study emphasizes the importance of structural mapping on active rift volcanoes to understand the geothermal field as well as potential volcanic hazards.

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“…The East African Rift System (EARS) hosts a number of large (>10 km diameter) silicic caldera systems [ Mohr et al ., ; Acocella et al ., ; Rampey et al ., , ; Robertson et al ., ]. Unlike similar‐sized volcanoes in developed nations, none of the EARS calderas are permanently monitored and in almost all cases knowledge of the frequency and magnitude of past eruptions is extremely limited [ Brown et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Causes of unrest at silicic calderas in the East African Rift: New constraints from InSAR and soil‐gas chemistry at Aluto volcano, Ethiopia

Hutchison

Biggs

Mather

et al. 2016

Geochem Geophys Geosyst

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Restless silicic calderas present major geological hazards, and yet many also host significant untapped geothermal resources. In East Africa, this poses a major challenge, although the calderas are largely unmonitored their geothermal resources could provide substantial economic benefits to the region. Understanding what causes unrest at these volcanoes is vital for weighing up the opportunities against the potential risks. Here we bring together new field and remote sensing observations to evaluate causes of ground deformation at Aluto, a restless silicic volcano located in the Main Ethiopian Rift (MER). Interferometric Synthetic Aperture Radar (InSAR) data reveal the temporal and spatial characteristics of a ground deformation episode that took place between 2008 and 2010. Deformation time series reveal pulses of accelerating uplift that transition to gradual long-term subsidence, and analytical models support inflation source depths of 5 km. Gases escaping along the major fault zone of Aluto show high CO 2 flux, and a clear magmatic carbon signature (CO 2 -d 13 C of 24.2& to 24.5&). This provides compelling evidence that the magmatic and hydrothermal reservoirs of the complex are physically connected. We suggest that a coupled magmatic-hydrothermal system can explain the uplift-subsidence signals. We hypothesize that magmatic fluid injection and/or intrusion in the cap of the magmatic reservoir drives edifice-wide inflation while subsequent deflation is related to magmatic degassing and depressurization of the hydrothermal system. These new constraints on the plumbing of Aluto yield important insights into the behavior of rift volcanic systems and will be crucial for interpreting future patterns of unrest.

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Physical volcanology of the Gubisa Formation, Kone Volcanic Complex, Ethiopia

Cited by 10 publications

References 30 publications

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

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

Structural controls on fluid pathways in an active rift system: A case study of the Aluto volcanic complex

Causes of unrest at silicic calderas in the East African Rift: New constraints from InSAR and soil‐gas chemistry at Aluto volcano, Ethiopia

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