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Addis Ababa, Ethiopia

Meshesha D.,Geological Survey of Ethiopia | Shinjo R.,University of Ryukyus
Journal of Mineralogical and Petrological Sciences | Year: 2010

This paper presents new hafnium isotope data for the Bure volcanic rocks from the northwestern Ethiopian plateau to constrain the nature of mantle sources within the broad mantle upwelling. The 176Hf/177Hf values range from 0.282901 (εHf = 4.79) to 0.283206 (εHf = 15.71) for the Oligocene transitional tholeiite and 0.282915 (εHf = 5.45) to 0.283069 (εHf = 10.85) for the alkaline basalts; these ratios are distinct from MORB but typical to OIB sources. The εHf values correlate positively with εNd. The scattered variation between εHf and contamination indices (such as Nb/La and Ce/Pb) for the transitional tholeiites implies that most tholeiitic basalts are affected by crustal contamination processes. Components 1 (C1) and 2 (C2), which are proposed to be the end-member components for the Afar mantle plume, have a Hf isotopic signature of εHf = 15-17 and 5-9, respectively. The diversity of these compositions relies on the proportion of recycled materials in the deep source, its formation age, and proportion of sediments relative to oceanic crust in the recycled materials. Source

Kebede S.,Geological Survey of Ethiopia
Transactions - Geothermal Resources Council | Year: 2014

Surface explorations for geothermal resources in Ethiopia began over three decades ago. The geothermal explorations so far have identified over 22 areas that have geothermal resources suitable for electricity generation, with a total potential of 10,000 MW. These resources are considered to have high quality in terms of temperature and chemistry. Despite the countries long term geothermal exploration and huge potential, the progress of development of geothermal resources has been slow. Deep drilling has been conducted only in two prospects and only a 7.2 MW pilot plant has been installed so far. However, since recent years the country has adopted, a renewable energy mix policy, geared towards the advancement of geothermal resources development, including other renewable energy resources. Accordingly both the public and private sector geothermal projects are being implemented at larger scale than before. The public sector has focused in developing, the two most explored prospects in the country, the Auto Langano and Tendaho geothermal fields. Under the public sector, geothermal power plants planned for commissioning by 2020 include: (i) 70 MW plant at Aluto Langano and 100 MW plant at Tendaho Additional geothermal power plants are expected to be commissioned at Corbetti geothermal field by private sector involvement, with a total capacity of 1000 MW, to be developed under various phases. Despite the recent efforts to advance geothermal development in Ethiopia, there are challenges that include: (i) high upfront capital costs required and availability of sufficient finance, (ii) risks associated with the exploration phase, and (iii) limitations in local human resource capacity and low level of experience in institutional set up, a legal and regulatory framework. Copyright © (2014) by the Geothermal Resources Council. Source

Admassu E.,Geological Survey of Ethiopia | Worku S.,Reykjavik University
Transactions - Geothermal Resources Council | Year: 2015

The area of investigation, Tulu-Moye, is situated in the Main Ethiopian Rift (MER) northwest of Asela close to the eastern margin of the rift. It is a wide zone where tectonic and volcanic activities are concentrated. As a major part of the Koka magmatic segment, The Tulu-Moye area has depicted interesting characteristics of volcanism and geologic structural patterns. The formation and growth of faults in the area could be explained by three progressive phases of faulting. Two fault models are proposed to explain the sequence of faulting, fracturing and lava flow events. The volcanic activities of the area are mostly controlled by the active faults and extension fractures of the Wonji Fault Belt (WFB). A fault morphology survey exhibited the various nature of the fault and fissure morphology that was primarily controlled by strike variations in the geologic units. The fault kinematic data collected from selected localities indicated E-W direction (∼ 93°) extension, consistent with previous works conducted in other parts of the MER. A comprehensive relationship between Quaternary faulting and magmatism was realized in the Tulu-Moye geothermal prospect. In such a way that, cone-fault, cone-lava and lava-fault interactions were the most noticeable relationships between Quaternary faulting and magmatism in the area. The fault morphology, fault model, fault-magmatism relationships, suggests a progressive development of an extension fissure to a mature normal fault. Tulu-Moye has both favorable geological and structural features for a prospective geothermal resource, which however deserves detail geothermal investigations towards defining the area's major parameters. Source

Shinjo R.,University of Ryukyus | Ginoza Y.,University of Ryukyus | Meshesha D.,University of Ryukyus | Meshesha D.,Geological Survey of Ethiopia
Journal of Mineralogical and Petrological Sciences | Year: 2010

An improved chemical separation method for Hf isotope ratio measurement using both the thermal ionization mass spectrometer (TIMS) and the multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) is presented in this paper. In the first column (2.5-ml Eichrom Ln-spec resin), Hf cut was collected with 2M HCl-0.2M HF after washing the major elements, HREE, Ti, Nb, and Zr. For further Hf purification, the second column (1-ml Ln-spec resin) chemistry was conducted in a manner similar to that of the first column. The first column is designed for treatment with a 0.5-g silicate rock sample for TIMS analysis. Thus, because the Hf amount required for MC-ICP-MS analysis is much lesser than that required for TIMS analysis, the column chemistry for MC-ICP-MS analysis can be scaled down, depending on the amount of digested sample. Although there is a need to improve the TIMS technique, the TIMS Hf data obtained for geological reference rocks and Ethiopian flood basalts after the application of the proposed separation methods are consistent, within analytical error, with the previously reported data obtained using the MC-ICP-MS. The advantages of the proposed method include a reduction in the amount of reagents used (hence, a consequent reduction in the blank contribution), reduction in the time required, and a simplified preparation requiring a fewer number of acids. Source

Blades M.L.,University of Adelaide | Collins A.S.,University of Adelaide | Foden J.,University of Adelaide | Payne J.L.,University of South Australia | And 5 more authors.
Precambrian Research | Year: 2015

The Western Ethiopian Shield (WES) forms a vast, underexplored, region of the East African Orogen. Lying towards the west of the orogen and between the dominantly juvenile Arabian-Nubian Shield in the north and the high-grade Mozambique Belt to its south, it holds a key position; vital in understanding the role of the East African Orogen in Gondwana formation. The WES is made up of a range of supra-crustal and plutonic rocks that formed in Tonian volcanic arc environments. The relative timing and duration of arc formation within the East African Orogen is still slowly being unravelled and we present new U-Pb and Hf isotopic data from zircons that help to define the maximum depositional age and provenance of the protoliths to meta-sedimentary units, as well as constrain the age of igneous intrusions located within the WES. Detrital zircons, obtained from a meta-sandstone, yield provenance age peaks at 2.8-2.4Ga, ca. 1.8Ga and 1.15-0.84Ga and a maximum depositional age of 838±13Ma. Hafnium isotopes from the same zircons demonstrate that both the oldest and youngest populations have broadly juvenile Hf isotopic values. However, the ca. 1.8Ga population shows significantly evolved Hf isotopic values. Sensitive High Resolution Ion MicroProbe (SHRIMP) U-Pb ages from two granites and a felsic granite and hornblende+biotite tonalite in the Nekempt-Ghimbi region of the Western Ethiopian Shield (Didesa and Kemashi Domains) indicate two pulses of magmatism at 850-840Ma and 780-760Ma. Partial melting and deformation in the Didesa Terrane occurred at ca. 660 Ma. Further west, the post-tectonic Ganjii granite yielded a 206Pb/238U age of 584±10Ma, constraining pervasive deformation in the area.Age constraints on orogenesis in the Western Ethiopian Shield (ca. 660. Ma) are similar to those in NE Uganda (ca. 690-660. Ma), but are older than the Ediacaran peak orogenesis reported from the Southern Ethiopian Shield, Eritrea and northern Ethiopia and from SE Kenya. This suggests that closure of the western Mozambique Ocean involved progressive volcanic-arc accretion to the active margin of Cryogenian-Ediacaran Africa. © 2015 Elsevier B.V. Source

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