Petrology of Flood Volcanism in Mertule Maryam, Northwestern Ethiopian Plateau, Central Ethiopia
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Date
2019-05-20
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Addis Ababa University
Abstract
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.
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Keywords
Ethiopian Plateau, Petrography, Stratigraphy, Phyric - Aphyric Texture, Plumbing, System, Shallow Crust, Simple Fractionation