A preliminary Geological and Generalized Stratigraphy of Western Margin of Northern Afar Depression, Dallol Area, Northern Ethiopia

The western margin of northern Afar Depression constitutes various rock units of Neoproterozoic basement complex, Paleozoic to Mesozoic sedimentary successions and the Oligocene to present volcano-sedimentary sequences. As part of a reconnaissance survey for mineral resources in selected districts of Afar region, a geological and structural map of Dallol area has been produced with the help of the Landsat Thematic Mapper Plus imagery at a scale of 1:100,000 and a simplified stratigraphy is constructed for the western rift margin, Dallol area.Keywords: Geology, Stratigraphy, Western Rift Margin, Dallol, Northern Afar Depression, Ethiopia

Geochemical and petrographic studies of the volcano-tectonic evolution of northern Afar

Der äthiopische Afar-Manteldiapir ist einer der jüngsten Diapirstrukturen der Welt. Seit ca. 30 Mio Jahren fördert er große Mengen an Magmen an die Erdoberfläche und trägt damit zur Umgestaltung der sublithosphärischen ostafrikanischen Kruste bei. Aufgrund der komplexen geodynamischen Natur dieser Region existiert eine eindruckvolle petrologische Vielfalt. Die Laven umfassen ein Spektrum von Basaniten zu tholeiitischen Basalten und von Phonoliten zu Trachyten. Diese Arbeit präsentiert geochemische und petrographische Untersuchungen an 93 vulkanischen, hauptsächlich basaltischen, Gesteinen, die aus den nördlichen äthiopischen Flutbasalten und der nördlichen Afar-Störung, der Erta`Ale Vulkankette, stammen. Sie beinhaltet ebenso eine kinematische Analyse der nördlichen und zentralen Afar-Störung, von deren ursprünglichen Beginn bis zur heutigen Ozeanbodenspreizung. Das Gesteinsmaterial stammt aus zwei Feldkampagnen: die erste fand 2007 in Vulkaniten des äthiopischen Hochlands statt, die zweite, 2008/09, hatte die axialen Basalte der nördlichen Afar-Senke zum Ziel. Es konnten viele petrologisch unterscheidbare vulkanischen Sequenzen im nördlichen äthiopischen Plateau und in der Afar-Senke identifiziert werden. Die ältesten vulkanischen Gesteine des Afar-Manteldiapirs werden durch die titanreichen (HT) und die titanarmen (LT) Gruppen der oligozänen Flutbasalte repräsentiert. Es kam jedoch auf der äthiopischen Hochebene sporadisch zur Eruption von in der Zusammensetzung variirenden Magmaserien. Eine dieser vulkanischen Serien setzt sich aus den, in einer kurzen Zeitspanne ausgetretenen, Axum post-Trappvulkaniten zusammen, eines geochemisch komplexen und lithologisch differierenden Teils der nordwestlichen äthiopischen Flutbasalt-Provinz. Nach dem Höhepunkt der äthiopischen Flutbasalteruption konzentrierte sich die magmatische Aktivität hauptsächlich auf Schildvulkane der Hochebene und auf riftgesteuerte Spaltbasalte am Grund der Afar-Senke. Zur Zeit beschränken sich die vulkanischen Aktivitäten komplett auf die axialen Bereiche der Afar-Senke, welche die letzte Phase des Afar-Manteldiapirs darstellen. Alle vorhandenen Spurenelementdaten und Isotopenuntersuchungen zeigen, dass sowohl die Plateaubasalte (Ti-reich) des Diapirkopfes, wie auch die axialen Basalte des Diapirendes eine nicht unterscheidbare Quellregion (OIB-Typ) besitzen, welche von der abgereicherten Mantelquelle abweicht. Die Konzentration der sehr inkompatiblen Elemente kann jedoch zwischen den einzelnen basaltischen Abfolgen variieren, was auf einen Wechsel im Aufschmelzungsgrad und -tiefe der Quellregion hinweist. Andererseits zeigen tektonische und geophysikalische Untersuchungen, dass die Afar-Senke zu den reinen Ozeankrusten-Typen gehört. Die Krustendicke der nördlichen Afar-Senke geht nicht über 15 km hinaus, die Spreizungs-Geschwindigkeit entlang der aktiven Erta´Ale Senke beträgt ca. 12 mm/Jahr/100 km. Es liegt auf der Hand, daß der Boden der nördlichen Afar-Senke ein ozeanischer ist, da seine Ausdehnungsraten denen des Roten Meeres und des Golfs von Aden enstpricht. Allerdings bestätigen die geochemischen Ergebnisse, dass der Magmatismus immer noch aus dem Rest des Afar-Manteldiapirs resultiert.The Ethio-Afar mantle plume is one of the youngest plume structures on earth that continually pours significant amounts of magmatic products to the surface of the earth for the last 30 Ma or more and reshaping the sublithospheric crust of east Africa. As a result of the complex geodynamic nature of the region, the petrologic diversity is very significant, the lavas ranging from basanites to tholeiitic basalts and phonolites to trachytes. This thesis presents geochemical and petrographic investigations of 90 volcanic rocks, mainly basaltic, from both the northern Ethiopian flood basalts and northern Afar Depression, the Erta’Ale Range. It also incorporates the kinematic analysis of the northern and central Afar Depression from incipient breakup to seafloor spreading. Rock sampling was performed in two field seasons: the first was in 2007 from the Ethiopian highland volcanic rocks and the second in 2008/09 from the northern Afar Depression axial basalts. Many petrologically distinct volcanic sequences in the northern Ethiopian plateau as well as Afar Depression have been identified. The oldest volcanic rocks of the Afar mantle plume are represented by the high-Ti (HT) and low-Ti (LT) groups of the Oligocene flood basalts. However, compositionally distinct magmatic series have been sporadically erupted in the Ethiopian highlands. One of these volcanic sequences is comprised of the Axum post-trap volcanics, a geochemically complex and lithologically varied part of the northwestern Ethiopian flood basalt province that erupted during a narrow time span. After the peak activity of the Ethiopian flood basalts, magmatic activities were mainly concentrated in the form of shield volcanoes in the plateau area and/or rift triggered fissure basalts in the floor of the Afar Depression. At present, volcanic activities are entirely confined along the axial zones of the Afar Depression representing the last phase of the Afar mantle plume (plume tail). All available trace element data and isotopic investigations show that both the high-Ti plateau basalts (HT2) from the plume head and the axial zone basalts from the plume tail have indistinguishable source regions (OIB-type), which are different from the depleted mantle source. However, the concentrations of the highly incompatible elements vary from one basaltic suite to another, showing a variation in degree and depth of melting of the source region. Structural and geophysical investigations (in the literature), on the other hand, show that the nature of the Afar Depression is purely an oceanic crust-type. Crustal thickness of the northern Afar Depression does not exceed 15 km and spreading rate along the actively expanding Erta’Ale Depression is ~12 mm/yr/100 km. This, obviously, implies that the floor of the northern Afar Depression is oceanic crust, as its spreading rate being analogous to the rates of the Red Sea and Gulf of Aden rifts; on the other hand, geochemical results confirm that magmatism resulted from the tail of the Afar mantle plume

Geochemistry of metavolcanics and granitic intrusive from western margin of northern afar depression, Dallol, Northern Ethiopia

The western margin of northern Afar Depression constitutes various rock units of Neoproterozoic basement complex. Major oxide data of metavolcanic and granitoid rock samples from basement complex indicate significant variation in the concentration of major oxides (e.g. Fe2O3, TiO2, CaO, MgO). Metavolcanic rocks of Dallol demonstrate heterogeneous nature of magma source. The mafic metavolcanics indicate two distinct groups, (i) CaO-enriched and (ii) tholeiitic composition. Another group of magmatic series, the felsic metavolcanic group, shows a co-genetic relationship with the tholeiitic metavolcanics. Granitoids on the other hand have a wider range of SiO2 (61.5 – 76.65 wt %) and are peraluminous to metaluminous in nature.Keywords: Geochemistry, Metavolcanics, Granitioids, Dallol, Northern Afar Depression, Ethiopia

High-resolution Data Based Groundwater Recharge Estimations of Aynalem Well Field

Due to the ever-increasing demand for water in Aynalem catchment and its surrounding, there has been an increased pressure on the Aynalem well field putting the sustainability of water supply from the aquifer under continuous threat. Thus, it is vital to understand the water balance of the catchment to ensure sustainable utilization of the groundwater resource. This in turn requires proper quantification of the components of water balance among which recharge estimation is the most important. This paper estimates the groundwater recharge of the Aynalem catchment using high-resolution hydro-meteorological data. Daily precipitation and temperature measurement data for years 2001-2018; groundwater level fluctuation records collected at every 30 minutes; and soil and land use maps were used to make recharge estimations. In the groundwater level fluctuation, three boreholes were monitored, but only two were utilized for the analysis because the third was under operation and does not represent the natural hydrologic condition. Thornthwaite soil moisture balance and groundwater level fluctuation methods were applied to determine the groundwater recharge of the Aynalem catchment. Accordingly, the annual rate of groundwater recharge estimated based on the soil-water balance ranges between 7mm/year and 138.5 mm/year with the weighted average value of 89.04 mm/year. The weighted average value is considered to represent the catchment value because the diverse soil and land use/cover types respond differently to allow the precipitation to recharge the groundwater. On the other hand, the groundwater recharge estimated using the groundwater level fluctuation method showed yearly groundwater recharge of 91 to 93 mm/year. The similarity in the groundwater recharge result obtained from both methods strengthens the acceptability of the estimate. It also points out that the previously reported estimate is much lower (36 to 66 mm/year)

Evaluation of groundwater resources in the Geba basin, Ethiopia

This article presents an assessment of the groundwater resources in the Geba basin, Ethiopia. Hydrogeological characteristics are derived from a combination of GIS and field survey data. MODFLOW groundwater model in a PMWIN environment is used to simulate the movement and distribution of groundwater in the basin. Despite the limited data available, by simplifying the model as a single layered semi-confined groundwater system and by optimising the transmissivity of the different lithological units, a realistic description of the groundwater flow is obtained. It is concluded that 30,000 m(3)/day of groundwater can be abstracted from the Geba basin for irrigation in a sustainable way, in locations characterised by shallow groundwater in combination with aquitard-type lithological units

Ultra-small microorganisms in the polyextreme conditions of the Dallol volcano, Northern Afar, Ethiopia

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars

Biogeochemical Cycling in Globally Distributed Hypersaline Environments

Studying extremophiles allows the characterisation of the boundaries of life on Earth and the identification of metabolic processes that fuel biogeochemical cycling under extreme conditions. Here we present an analysis of the microbiomes of globally distributed hypersaline environments. We screened published metagenomes produced from a range of hypersaline environments (Marine salterns in Spain, hypersaline lakes in Chile and Antarctica, and soda lakes in Egypt and Mongolia [1–5]) for the presence, diversity, and abundance of shared functional genes that encode for the enzymes relevant to biogeochemical cycling. The study was expanded by generating metagenomes from DNA extracted from the salt and water of an Ethiopian hypersaline lake in the Dallol Depression. Analysis was performed to compare the functional gene profiles between the hypersaline environments. The microbial community within the Ethiopian Lake was comprised of Cyanobacteria, Candidate Phyla, and halophilic bacteria and archaea. Screening of the metagenomes identified that phototrophs in hypersaline environments typically possessed the majority of the genes relating to carbon dioxide and nitrogen fixation, indicating that they play a major role in driving both the carbon and nitrogen cycles [6-7]. High abundances of genes involved in denitrification, methylamine utilisation, and carbon monoxide oxidation classified as Halobacterial were also identified in all the metagenomes, indicating that these taxa are also key players in biogeochemical cycling in hypersaline environments [8-9]. Cultivation efforts are required to further define the interactions between the distinct functional clades identified in the hypersaline environments. References: 1. Zhao D, Zhang S, Xue Q, Chen J, Zhou J, Cheng F, et al. Front Microbiol. 2020;11(July):1–17. 2. Hagagy N, Hamedo H, Elshafi N, Selim S. Shotgun Metagenomic Sequencing of Extremophilic Community from Soda Lake, Ga’ar Lake, in Wadi Al-Natrun, Egyt. Egypt. J. Exp. Biol. (Bot.). 2021;1. 3. Fernandez AB, Ghai R, Martin-Cuadrado AB, Sanchez-Porro C, Rodriguez-Valera F, Ventosa A. Genome Announc. 2013;1(6). 4. Yau S, Lauro FM, Williams TJ, Demaere MZ, Brown M v., Rich J, et al. ISME Journal. 2013;7(10):1944–61. 5. Kurth D, Elias D, Rasuk MC, Contreras M, Farias ME. PLoS One. 2021;16:1–21. 6. Lay CY, Mykytczuk NCS, Yergeau É, Lamarche-Gagnon G, Greer CW, et al. Appl Environ Microbiol 2013;79:3637–3648. 7. Mehda S, Ángeles Muñoz-Martín M, Oustani M, Hamdi-Aïssa B, Perona E, et al. Microorganisms 2021;9:1–27. 8. Sorokin DY, Merkel AY, Messina E, Tugui C, Pabst M, et al. ISME J 2022;1–13. 9. King GM. Proc Natl Acad Sci 2003;51:278–291. Acknowledgements to the Europlanet Society, Science and Technology Facilities Council and the Research England Expanding Excellence in England (E3) fund for funding the research