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Petrogenesis of Oligocene volcanic rocks of the lake tana area,Ethiopian large Igneous Province

Acta Geochimica 2023年第6期42卷 1104-1123页

作者： Ayenachew Alemayhou Desta Asfawossen Asrat Minyahl Teferi Desta Department of Geology School of Earth SciencesBahir Dar UniversityP.O.Box 79Bahir DarEthiopia Department of Mining and Geological Engineering Botswana International University of Science and TechnologyPrivate Bag 16PalapyeBotswana School of Earth Sciences Addis Ababa UniversityP.O.Box 1176Addis AbabaEthiopia

The lake tana area is located within a complex volcano-tectonic basin on the northwestern Ethiopian *** basin is underlain by a thick succession of Oligocene transitional basalts and sub-alkaline rhyolites overlain in places,particularly south of the lake,by Quaternary alkaline to mildly transitional basalts,and dotted with Oligo-Miocene trachyte domes and *** paper presents the results of integrated field,petrographic,and major and trace element geochemical studies of the lake tana area volcanic rocks,with particular emphasis on the Oligocene basalts and *** studies reveal a clear petrogenetic link between the Oligocene basalts and *** Oligocene basalts are:(1)plagioclase,olivine,and/or pyroxene phyric;(2)show an overall decreasing trend in MgO,Fe_(2)O_(3),and CaO with silica;(3)have relatively low Mg#,Ni and Cr contents and high Nb/La and Nb/Yb ratios;and(4)show LREE enriched and generally flat HREE *** these imply the origin of the Oligocene basalts by shallow-level fractional crystallization of an enriched magma sourced at the asthenospheric *** Oligocene rhyolites:(1)are enriched in incompatible while depleted in compatible trace elements,P and Ti;(2)show a strong negative Eu anomaly;(3)contain appreciable amounts of plagioclase,apatite,and Fe-Ti oxides;and(4)show clear geochemical similarity with well-constrained rhyolites from the Large Igneous Province(LIP)of the northwestern Ethiopian ***-pressure fractional crystallization of mantle-derived basaltic magma in crustal magma chambers explains the origin of these *** study further shows that the Oligocene basalts and rhyolites are co-genetic and the felsic rocks of the lake tana area are related differentiates of the flood basalt volcanism in the northwestern Ethiopian plateau.

关键词： Large igneous province Oligocene basalt Oligocene rhyolite Fractional crystallization lake tana

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Hydrological Impact Assessment of Climate Change on lake tana’s Water Balance, Ethiopia

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American Journal of Climate Change 2016年第1期5卷 27-37页

作者： Zemede Mulushewa Nigatu Tom Rientjes Alemseged Tamiru Haile Hawassa University WGFC-NR Hawassa Ethiopia University of Twente ITC Enschede The Netherlands International Water Management Institute (IWMI) Addis Ababa Ethiopia

The aim of this study is to evaluate the hydrological impacts of climate change on the water balance of lake tana in Ethiopia. Impact assessments are by downscaled General Circulation Model (GCM) output and hydrological modeling. For A2 and B2 emission scenarios, precipitation, maximum and minimum temperature estimates from the HadCM3 GCM were used. GCM output was downscaled using the Statistical DownScaling Model (SDSM 4.2). Impact analyses were applied for three future time periods: early, mid and late 21st century. Over-lake evaporation is estimated by Hardgrave’s method, and over-lake precipitation is estimated by inverse distance weighing interpolation, whereas inflows from gauged and ungauged catchments are simulated by the HBV hydrological model. Findings indicate increases in maximum and minimum temperature on annual base for both emission scenarios. The projection of mean annual over lake precipitation for both A2 and B2 emission scenarios shows increasing pattern for 21st century in comparison to the baseline period. The increase of mean annual precipitation for A2 emission scenario is 9% (112 mm/year), 10% (125 mm/year) and 11% (137 mm/year) for the three future periods respectively. B2 emission scenario mean annual precipitation shows increase by 9% (111 mm/year), 10% (122 mm/year) and 10% (130 mm/year) respectively for the three future periods. Findings indicate consistent increases of lake storage for all three future periods for both A2 and B2 emission scenarios.

关键词： Climate Change Water Balance SDSM Statistical Downscaling lake tana

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Comparative study on composition and abundance of major planktons and physico-chemical characteristics among two ponds and lake tana,Ethiopia

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Journal of Coastal Life Medicine 2015年第11期 852-856页

作者： Wondie Zelalem Amanu Bahir Dar Fishery and Other Aquatic Life Research Center P.O.Box 794Bahir DarEthiopia

Objective:To evaluate the difference in physico-chemical characteristics,composition and abundance of plankton communities owing to the supplementary feed added in fish ponds as compared to lake ***:Physico-chemical and biological data of plankton were collected from 3 studied sites from November 2008 to October *** were compared using One-way ANOVA to see the difference among *** indices such as Margalef's index,Shannon-Wiener index,and evenness index were employed to describe the distribution of plankton community among the studied ***:The pH value was remarkably higher in ponds ***,conductivity and total dissolved solids were the highest in lake *** concentration was relatively high in *** species richness was higher in lake water than *** lake also had the highest mean value of both Shannon-Wiener index and evenness index in ***:The results revealed that the supplementary feed added to each pond had influence on nutrient content which enhanced algal biomass and productivity of the ***,the pond water has to be regularly refreshed to control eutrophication.

关键词： Aquaculture lake tana Pond water Plankton Abundance Diversity

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