Browsing by Author "Berlie, Getie"

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    Geochemical Studies of Volcanic Rocks for the Implication of their Petrogenesis in Between Southern Lake Hayk and Western Part of Lake Hardibo South Wollo Amhara Regional State Ethiopia
    (Addis Ababa University, 2021-09-14) Berlie, Getie; Ayalew, Dereje (Professor)
    The study area is located around Lake Hayk northeastern central part of Ethiopian. In this study petrographic, and geochemical (trace and major elements) data of mafic to felsic rock are presented, integrated, and interpreted to characterize the geochemistry of cogenetic suite and petrogenetic processes involved in the evolution of these flood basalts to differentiated rhyolite rock units. Fieldwork for sampling and mapping, petrographic investigations, and major and trace element geochemical analysis using ICP-AES and ICP-MS procedures are all completed to meet this objective. The area constitutes of bimodal composition of flood basaltic to rhyolitic rock with scarce intermediate composition. The rock units that make up the research area are basalt, basaltic andesite, trachydacite, and rhyolite, based on total alkalis versus silica (TAS) classification. The basaltic rock (La/Yb) N ratio = (5.34-10.97), basaltic andesite to rhyolite (La/Yb) N ratio = (6.19-11.74), basalt is less to moderately fractionated than moderately fractionated basaltic andesite to rhyolite. The basalt, basaltic andesite to rhyolite samples have ratios of Ce/Pb >19.65-33.2 and 6.13-15.6 respectively and basalt sample has ratios of Nb/U = 39.55- 45.81 and basaltic andesite to rhyolite have Nb/U= 21.59-33.68 and basalt and basaltic andesite to rhyolite has ratios of Nb/Th=9.7-12.3, 5.08-8.63 respectively. Basalt have low Rb/Nb = 0.5-0.58, La/Nb = 0.88-1.06 and high TiO2 = 2.08-3.04,basaltic andecite have higher Rb/Nb =2.7, La/Nb = 1.81 and low TiO2 1.96 and rhyolite Rb/Nb = 0.97-1.69, La/Nb = 0.51-1.08 and lower TiO2 = 0.41- 0.71.MgO against incompatible trace elements such as Th, La, and U has a negative correlation this testifies that there is insignificant continental crust involvement and Ce/Pb displays a positive correlation with MgO suggest that there is minimal crustal contamination. The positive and negative anomalies of Ba and K respectively, testify related to amphibole mantle source. The basaltic rock unit characterized by low CaO/Al2O3 ratios (0.71–0.99) and relatively no fractionation and flat HREE patterns with (TbN/YbN = 1.75-2.33) chondritic values this suggest a mantle source mostly containing spinel rather than garnet and the gentle slope in HREE show the source for mafic rock is garnet free. Rhyolite is characterized by a steep negative correlation in bivariate major oxides such as MgO,Fe2O3,TiO, and CaO against SiO2 and positive anomaly of Ta with slight Nb trough which implicate that Rhyolites formed by fractional crystallization rather than significant crustal contribution, partial melting and assimilation. Detail isotope geochemistry and mineral chemistry studies are much recommended around Lake Hayk.