The volcano–pluton interface; The Longonot (Kenya) and Kûngnât (Greenland) peralkaline complexes

MacDonald, Raymond J.; Bagiński, Bogusław; Upton, B. G. J.

doi:10.1016/j.lithos.2014.03.009

Cited by 13 publications

(9 citation statements)

References 57 publications

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“…Deformation data alone do not allow us to investigate these possibilities, nor do they unambiguously differentiate between whether the fluid is gas, aqueous fluid, magma, or a combination of these. However, most peralkaline volcanoes are considered to have a volatile‐rich cap at around 5–6 km depth [e.g., Leat et al ., ; Mattia et al ., ; Biggs et al ., ; Neave et al ., ; Macdonald et al ., ]. This zone is consistent with our modeled source depth (Figure c) and our interpretation is that magmatic fluid injection or intrusions into this cap provide the source mechanism for uplift at Aluto (Figure ).…”

Section: Causes Of Unrestmentioning

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

100

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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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Section: Causes Of Unrestmentioning

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

100

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“…Rooney et al, 2012), whereas, we have focused on smaller volume, post-caldera eruptive episodes. Variations in the incompatible trace element compositions at Aluto since ~60 ka can be explained by crystal fractionation in a compositionally zoned cap of a shallow magmatic reservoir (Macdonald et al, 2014;Hutchison et al, 2016b). Larger volume caldera forming eruptions are likely to be sourced from a larger chamber over a greater depth interval, polybaric models are therefore more relevant to these larger eruptions.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Constraining magma storage conditions at a restless volcano in the Main Ethiopian Rift using phase equilibria models

Gleeson

Stock

Pyle

et al. 2017

Journal of Volcanology and Geothermal Research

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The Main Ethiopian Rift hosts a number of peralkaline volcanic centres, with many showing signs of recent unrest. Due, in part, to the low number of historical eruptions recorded in the region, volcanism in the Main Ethiopian Rift remains understudied relative to other volcanic settings and conditions of magma storage remain almost entirely unknown. Aluto is one of these restless caldera systems and identifying magma storage conditions is vital for evaluating the risks posed by recent periods of unrest. In this study, we ran ~150 fractional crystallisation models, using the Rhyolite-MELTS thermodynamic software, within the range P = 50-300 MPa, starting H 2 O = 0.5-3 wt% and fO 2 = QFM-2-QFM+1. This represents a realistic range of potential magma storage conditions at Aluto. We assessed the fractionation trends produced using two different starting compositions, which represent different estimates of the parental melt feeding the system. The predicted liquid lines of descent produced by these models are compared with Aluto whole-rock data from the literature, and are presented along with new observations of the natural phase assemblage and erupted mineral compositions to provide information on the magma storage conditions.

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“…Volcanism across Kenya, for example, varied spatially and temporally, leading to a diverse suite of weakly (olivine basalts, trachytes, trachyphonolites and alkali rhyolites) to strongly (nephelinites, basanites, alkali basalts, tephrites and phonolites) alkaline volcanics (e.g. Williams, ; McDougall & Brown, ) with mixed basalt, trachyte, rhyolite and commendite lavas associated with individual Quaternary volcanoes (Baker et al ., , ; Macdonald, ; Macdonald et al ., ). These contrasting lithologies are characterized by different trace element suites that influence lake sediment geochemistry.…”

Section: Discussionmentioning

confidence: 97%

Spatial and temporal geochemical variability in lacustrine sedimentation in the East African Rift System: Evidence from the Kenya Rift and regional analyses

2018

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Many previous studies on lacustrine basins in the East African Rift System have directed their attention to climatic controls on contemporary sedimentation or climate change as part of palaeoenvironmental reconstruction. In contrast, this research focuses on the impact of tectonism and volcanism on rift deposition and develops models that help to explain their roles and relative importance. The study focuses on the spatial and temporal variability in bulk sediment geochemistry from a diverse range of modern and ancient rift sediments through an analysis of 519 samples and 50 major and trace elements. The basins examined variously include, or have contained, wetlands and/or shallow to deep, fresh to hypersaline lakes. Substantial spatial variability is documented for Holocene to modern deposits in lakes Turkana, Baringo, Bogoria, Magadi and Malawi. Mio‐Pleistocene sediments in the Central Kenya Rift and Quaternary deposits of the southern Kenya Rift illustrate temporal variability. Tectonic and volcanic controls on geochemical variability are explained in terms of: (i) primary controlling factors (faulting, subsidence, uplift, volcanism, magma evolution and antecedent lithologies and landscapes); (ii) secondary controls (bedrock types, rift shoulder and axis elevations, accommodation space, meteoric and hydrothermal fluids and mantle CO2); and (iii) response factors (catchment area size, orographic rains, rain shadows, vegetation densities, erosion and weathering rates, and spring/runoff ratios). The models developed have, in turn, important implications for palaeoenvironmental interpretation in other depositional basins.

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The volcano–pluton interface; The Longonot (Kenya) and Kûngnât (Greenland) peralkaline complexes

Cited by 13 publications

References 57 publications

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

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

Constraining magma storage conditions at a restless volcano in the Main Ethiopian Rift using phase equilibria models

Spatial and temporal geochemical variability in lacustrine sedimentation in the East African Rift System: Evidence from the Kenya Rift and regional analyses

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