Geology, Petrology and Geochemistry of Volcanic Rocks Around Arba Minch, Southern Ethiopia
Volume 8, Issue 3, June 2019, Pages: 160-168
Received: Apr. 24, 2019;
Accepted: May 28, 2019;
Published: Jun. 12, 2019
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Gosaye Berhanu, Department of Geology, Arba Minch University, Arba Minch, Ethiopia
The study area is subpart of the southern main Ethiopian Rift and geographically bounded between UTM (Universal Transverse Mercator) coordinates of 662000m-669000m latitude and 336000m-341000m longitude. The main aim of this study is to investigate the geological, petrographic and geochemical properties of volcanic rocks around Arba Minch, southern Ethiopia. Both field and laboratory analytical techniques are employed to characterize minerals and the rock types. Eight thin section samples are prepared to study petrographic properties of minerals and five best representative samples are analyzed for whole rock chemistry using ICP-MS (Inductively Coupled Plasma-Mass Spectrometry). Petrographically, samples from the porphyritic basalt show phenocrysts of olivine and plagioclase within the fine-grained groundmass. There are rounded to subrounded holes or vesicles that appear white under plane polarized light observations and dark under cross polarized light observations which further confirms vesicular nature of the basalt. Thin section sample from rhyolite outcrop shows phenocrysts of K-feldspar and quartz within tiny fine-grained groundmass of feldspar minerals. Aphanitic basalt, Porphyritic basalt, vesicular basalt, rhyolite and dolerite are the rock units found in the study area. The geochemical results of the analyzed samples indicate silica ranges of (48.5-60.1)%. Based geochemical classifications made, rock units are classified into rhyolite, basalt, hawaiite and mugherite rock types. Trace element analytical results show all samples lie on the within plate tectonic setting. The rare earth and trace element ratios and spider diagrams confirmed that most samples are derived from magmas of asthenospheric source with little crustal contamination.
Geology, Petrology and Geochemistry of Volcanic Rocks Around Arba Minch, Southern Ethiopia, Earth Sciences.
Vol. 8, No. 3,
2019, pp. 160-168.
Bellahsen, N., C. Faccenna, F. Funiciello, J. M. Daniel, and L. Jolivet (2003). Why did Arabia separate from Africa? Insights from 3-D laboratory experiments. Earth Planet. Sci. Lett.
Bonini, M., Corti, G., Innocenti, F., Manetti, P., Mazzarini, F., Abebe, T., Pecskay, Z., 2005. Evolution of the Main Ethiopian Rift in the frame of Afar and Kenya rifts propagation.
Boynton W V (1984). Cosmochemistry of the rare earth elements: meteorite studies. In: Henderson P (eds) Rare Earth Element Geochemistry. Elsevier, Amsterdam, pp 63-114.
Cox K G, Bell J D & Pankhurst (1979) The Interpretation of Igneous Rocks. Allen & Unwin, London.
De La Roche H, Leterrier J, Grandclaude P, & Marchal M (1980). A classification of volcanic and plutonic rocks using R1-R2- diagram and major element analyses - its relationships with current nomenclature. Chem Geol 29: 183-210 doi: 10.1016/0009-2541 (80) 90020-0.
Ebinger, C. J., T. Yemane, D. J. Harding, S. Tesfaye, S. Kelley, and D. C. Rex (2000). Riftmigration and propagation: Linkage of the Ethiopian and Eastern rifts, Africa, Geol. Soc.Am. Bull.
Fitton JG, James D, Kempton PD, Ormerod DS, Leeman WP (1988). The role of lithospheric mantle in the generation of late Cenozoic basic magmas in the western United States. In: Cox KG, Menzies MA, editors. Oceanic and Continental Lithosphere: Similarities and Differences.
Ghebreab, W (1998). Tectonics of the Red Sea region reassessed, Earth Sci. Rev.
Kazmin, V (1975). Explanation of the geological map of Ethiopia. Ethiopian Institute of Geological Surveys, Bull. No. 1.
Leat PT, Thompson RN, Morrison MA, Hendry GL, Dickin AP (1988). Compositionally-diverse Miocene-recent rift related magmatism in northwest Colorado: partial melting, and mixing of mafic magmas from three different asthenospheric and lithospheric mantle sources.
Mojgan S (2008). Petrology, geochemistry and mineral chemistry of extrusive alkalic rocks of the Southern Caspian Sea ophiolite, Northern Alborz, Iran: evidence of alkaline magmatism in Southern Eurasia.
Morley, C. K., W. A. Wescott, D. M. Stone, R. M. Harper, S. T. Wigger, and F. M. Karanja (1992). Tectonic evolution of the northern Kenyan Rift, J. Geol. Soc. London.
Pearce JA (1982). Trace elements characteristics of lavas from destructive plate boundaries. In: Thorpe RS, editor. Andesites. Chichester, UK.
Pearce JA, Norry MJ (1979). Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contrib Mineral Petrol.
Sun, S. s., Mc Donough, W. F (1989). Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, In: A.D. (Ed.), Magmatism in the Ocean Basins. Geological Society, London.
Tadiwos Cherinet (2011). Geology and hydrothermal resources in the northern Lake Abaya area (Ethiopia). Journal of African Earth Sciences.
W. Hutchison, T. A. Mather, D. M. Pyle, A. J. Boyce, M. L. M. Gleeson, G. Yirgu, J. D. Blundy, D. J. Ferguson, C. Vye-Brown, I. L. Millar, K. W. W. Sims and A. A. Finch (2018). The evolution of magma during continental rifting: new constraints from the isotopic and trace element signatures of silicic magmas from Ethiopian volcanoes, Earth and Planetary Science Letters, 489, 203-218, 2018. (doi: 10.1016/j.epsl.2018.02.027).