Gravity field and isostatic state of Ethiopia and adjacent areas |
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| Institution: | 1. Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via Saragat 1, 44100 Ferrara, Italy;2. Department of Earth Sciences, University of New Hampshire, Durham, NH 03824, USA;3. Laboratoire de Géologie de Lyon, CNRS UMR 5276, Ecole Normale Supérieure de Lyon and Université Claude Bernard Lyon 1, 46 Allée d''Italie, 69007 Lyon, France;4. College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97321, USA;1. School of Earth Sciences, University of Bristol, Wills Memorial Building, Queens Road, Bristol BS8 1RJ, UK;2. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;3. Institute of Geophysics, Space Science, and Astronomy, Addis Ababa University, Addis Ababa, Ethiopia;1. School of Earth Sciences, Addis Abeba University, P.O. Box 1176, Addis Abeba, Ethiopia;2. IGAG-CNR, Rome, Italy;3. Sapienza Università di Roma, Rome, Italy;1. Dept. of Earth and Environmental Sciences, Michigan State University, East Lansing, MI 48824. United States;2. Department of Earth Science and Engineering, Imperial College London, London SW7 2AZ, UK;3. Dept. of Earth Sciences, Addis Ababa University, Addis Ababa, Ethiopia;4. Dept. Geology, Pomona College, Claremont, CA, United States;5. Tonagharraun, Corrandulla, Ireland;6. CEPS MRC 315, Smithsonian Institution, Washington D.C., DC, United States;7. Dept. Geology & Planetary Science, University of Pittsburgh, Pittsburgh, PA, United States |
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| Abstract: | Over 35,000 onshore and offshore gravity stations have been compiled in order to test isostatic models against geologic structures over a part of the Afro–Arabian shield. The area of Ethiopia covers an important part of this system because it contains the major section of the ≈5000 km Afro–Arabian rift and includes the transition between the Arabo-Nubian-Shield (ANS) and the Mozambique Belt (MB).Isostatic residual anomalies have been calculated using both Airy and Vening-Meinesz (flexural rigidity D = 1022 Nm) models. The isostatic residual anomalies outline the major Precambrian belts, the Cenozoic rifts and associated major structures. Positive residual anomalies associated with the main Ethiopian Rift (MER) and Kenyan rift systems could be the expressions of an axial intrusive body and swarms of local faults and fractures. The residual anomalies indicate relative stability in the MER and increased tectonic activity in the areas of the Red Sea, Gulf of Aden and Afar. Near-zero isostatic residuals flank the MER and Kenya rifts and are found within the Danakil Alps and some plateau regions.The small mean isostatic residual anomaly (about 8 mGal) and the isostatic analysis show a slight positive bias indicating under compensation. The undercompensation may imply that there are upper crustal features that are not compensated regionally (probably supported by the rigidity of the lithosphere) and isostatic disequilibrium in the region. Therefore, the high topography of Ethiopia and East African plateau is partly compensated by thicker crust (broad negative isostatic regional anomaly) and partly by dynamic forces.The results of the qualitative interpretation form the basis of continuing three-dimensional gravity modelling and quantitative analysis that also integrates data from eastern Sudan. |
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