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

This work is a contribution to the Natural Environment Research Council (NERC) funded RiftVolc project (NE/L013932/1, Rift volcanism: past, present, and future). W.H., T.A.M., and D.M.P. are supported by and contribute to the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes, and Tectonics (COMET). W.H. M.J.S. were supported by a NERC studentships NE/J5000045/1 and NE/K500811/01 respectively.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 H2O = 0.5–3 wt% and fO2 = 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. Using a new, quantitative statistical approach to compare empirical data and thermodynamic model-outputs, we find that the compositions of evolved peralkaline rhyolites from Aluto are best reproduced by isobaric fractional crystallisation from a rift-related basaltic composition, without the need for significant crustal assimilation. Around 90% protracted fractional crystallisation is required to produce these compositions. This indicates that the magmatic system is likely to exist as a highly crystalline mush. The best agreement between models and natural samples is at low pressures (150 MPa), low initial H2O concentrations (0.5 wt%) and relatively high oxygen fugacity (QFM). The depth of magma storage derived from these results (~ 5.6 ± 1 km) agrees well with the source depths modelled from measured ground deformation at Aluto in 2008. Data from other peralkaline volcanic centres in the Main Ethiopian Rift, such as Boset and Gedemsa, and at other locations globally (e.g. Pantelleria, Italy) suggest that these storage conditions are a common feature of many peralkaline volcanic centres. Our data is consistent with the formation of a Daly Gap at Aluto due to compositional stratification of the magma reservoir beneath the caldera, and the non-linear relationship between temperature and SiO2 concentration during magmatic differentiation.PostprintPeer reviewe

Melting during late-stage rifting in Afar is hot and deep

Investigations of a variety of continental rifts and margins worldwide have revealed that a considerable volume of melt can intrude into the crust during continental breakup, modifying its composition and thermal structure. However, it is unclear whether the cause of voluminous melt production at volcanic rifts is primarily increased mantle temperature or plate thinning. Also disputed is the extent to which plate stretching or thinning is uniform or varies with depth with the entire continental lithospheric mantle potentially being removed before plate rupture. Here we show that the extensive magmatism during rifting along the southern Red Sea rift in Afar, a unique region of sub-aerial transition from continental to oceanic rifting, is driven by deep melting of hotter-than-normal asthenosphere. Petrogenetic modelling shows that melts are predominantly generated at depths greater than 80 kilometres, implying the existence of a thick upper thermo-mechanical boundary layer in a rift system approaching the point of plate rupture. Numerical modelling of rift development shows that when breakup occurs at the slow extension rates observed in Afar, the survival of a thick plate is an inevitable consequence of conductive cooling of the lithosphere, even when the underlying asthenosphere is hot. Sustained magmatic activity during rifting in Afar thus requires persistently high mantle temperatures, which would allow melting at high pressure beneath the thick plate. If extensive plate thinning does occur during breakup it must do so abruptly at a late stage, immediately before the formation of the new ocean basin

Long-term consequences of the misuse of ivermectin data

Ivermectin is an oral anti-infective medicine that is integral to neglected tropical disease programmes. It is safe and effective for the treatment and control of lymphatic filariasis, scabies, and onchocerciasis, sometimes as part of a mass drug administration, as recognised in the WHO road map for neglected tropical diseases 2021–30. The WHO essential medicines list provides recommendations for minimum medicine needs for a basic health-care system, which includes ivermectin as an anthelmintic, antifilarial, and antiectoparasitic treatment. There has been a groundswell of opinion across several countries that ivermectin might be useful in reducing the symptoms of and mortality due to COVID-19, with many citing meta-analyses that infer positive effects; however, these conclusions appear to be unreliable

Event trees and epistemic uncertainty in long‐term volcanic hazard assessment of Rift Volcanoes: the example of Aluto (Central Ethiopia)

Aluto is a peralkaline rhyolitic caldera located in a highly populated area in central Ethiopia. Its postcaldera eruptive activity has mainly consisted of self‐similar, pumice‐cone‐building eruptions of varying size and vent location. These eruptions are explosive, generating hazardous phenomena that could impact proximal to distal areas from the vent. Volcanic hazard assessments in Ethiopia and the East African Rift are still limited in number. In this study, we develop an event tree model for Aluto volcano. The event tree is doubly useful: It facilitates the design of a conceptual model for the volcano and provides a framework to quantify volcanic hazard. We combine volcanological data from past and recent research at Aluto, and from a tool to objectively derive analog volcanoes (VOLCANS), to parameterize the event tree, including estimates of the substantial epistemic uncertainty. Results indicate that the probability of a silicic eruption in the next 50 years is highly uncertain, ranging from 2% to 35%. This epistemic uncertainty has a critical influence on event‐tree estimates for other volcanic events, like the probability of occurrence of pyroclastic density currents (PDCs) in the next 50 years. The 90% credible interval for the latter is 5–16%, considering only the epistemic uncertainty in conditional eruption size and PDC occurrence, but 2–23% when adding the epistemic uncertainty in the probability of eruption in 50 years. Despite some anticipated challenges, we envisage that our event tree could be translated to other rift volcanoes, making it an important tool to quantify volcanic hazard in Ethiopia and elsewhere

Using lake sediment cores to improve records of volcanism at Aluto volcano in the main Ethiopian rift

info:eu-repo/semantics/publishe

Survey on the geology of Welmera Woreda (Shoa)

Includes map in back pocke

Preface

1. Introduction Our planet represents a dynamic system in which the atmosphere, hydrosphere, lithosphere, and biosphere are constantly interacting and where natural cycles that involve water, rocks, and atmospheric gases play their part in supporting and sustaining life. Natural Earth processes shape landscapes and maintain the planet’s environments by constantly reworking, conserving, and renewing its materials. An understanding of our Earth, its processes, and its geological history, is the key to an ecologically sustainable development of the planet’s resources. The East African Rift System (EARS), being the most spectacular continental rift in the world, has long been a classic area for investigating continental rifting and break-up. The study of continental rifts is of particular interest because they are believed to represent the initial stages of continental breakup and passive margin development where oil-bearing as well as climate-sensitive sediments accumulate, and whose architecture and tectonics might have controlled human evolution in the past and localization of geologic hazards at present. The EARS cuts through the Afar and East African plateaus and extends 3000 km from the Afar depression in the north to Okavango Delta in the south. Along with the Gulf of Aden and the Red Sea oceanic rifts, it forms the third arm of the triple junction at Afar depression. The EARS overlies one of the largest thermal anomalies in the Earth’s mantle and comprises fault systems of different ages as well as nascent seafloor spreading centers in Afar. The desire to investigate and fully understand the evolution of EARS and its environments at different scales invites the synergy of several Earth science disciplines. Following this philosophy, we have edited this volume entitled “The East African Rift System: Dynamics, Evolution and Environment” with the objective of providing an integrated approach in the study of the rift system. Most of the papers in this issue are extracted from an international conference entitled ‘The East African Rift System: Development, Evolution and Resources’ that was held in Addis Ababa, Ethiopia in June 2004. A subset of the papers presented at this conference has been published in a special volume of the Geological Society of London (SP 259, 2006). In this meeting organized by the Ethiopian Geoscience and Mineral Engineering Association (EGMEA), more than 100 geoscientists attended and were treated to 66 presentations on a broad range of topics, including rift geodynamics, geophysics, tectonics, magmatism, sedimentation, environment, geohazards and resources. We feel that producing this special volume in its present form is convenient for readers to get a glimpse on the current developments of the EARS