Petrology of Flood Volcanism in Mertule Maryam, Northwestern Ethiopian Plateau, Central Ethiopia

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Addis Ababa University


Mertule Maryam flood volcanism terrain is situated in the southern part of the northwestern Ethiopian plateau. The area is located 364 Km from Addis Ababa. The main objective of the thesis work is to understand the petrography and stratigraphy of Mertule Maryam area volcanic products and finally to assess the magmatic evolution. To accomplish the objectives, starting from the beginning various methods have been applied. The methods are; remote sensing, field observation, stratigraphy, petrography and geochemistry. The major volcanic units are plagioclase- pyroxene phyric basalt, agglomerate, aphyric basalt, plagioclase phyric basalt and undifferentiated aphyric basalt and tuff. The Mertule Maryam area volcanic products show narrow variation in composition of SiO2 percentage (47.7 – 51 wt %) as mafic suits. Petrographic and stratigraphic observation of mafic samples from the study area suggested three divisions within the study area. These are dominantly plagioclasepyroxene phyric, aphyric flow and plagioclase phyric flood basalt units. This distinctive petrographic heterogeneity reveals difference in depth of fractionation and magma flux in the lithosphere. The presence of plagioclase-pyroxene phyric basalt indicates there is considerable depth of fractionation in the shallow plumbing system. The aphyric basalt flow unit reflects there is no fractionation of any mineral in the shallow crust this indicates that the rate of magma flux to the shallow plumbing system is high. In addition the presence of plagioclase phyric basalt suggested that there was fractionation in the shallow plumbing system. Selected variation diagrams for major element and trace element shows scattered plot pattern which suggests these volcanic products are not the result of simple fractionation instead they do have different ways to come to the lithosphere.



Ethiopian Plateau, Petrography, Stratigraphy, Phyric - Aphyric Texture, Plumbing, System, Shallow Crust, Simple Fractionation