Petrographic Description and Structural History of the Megab-Hawzien Area, Tigray, Northern Ethiopia

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Addis Ababa University


The Megab - Hawzien area is a part of the Neoproterozoic basement rocks of Northern Ethiopia. The Northern Ethiopia is one of the regions where the basement units consisting of older, low-grade meta-volcanic rocks known as the Tsaliet Group and younger, low grade meta-sedimentary rocks referred to the Tambien Group. These low-grade meta-volcanic and meta-sedimentary rocks have long been considered to be part of the Arabian-Nubian Shield. The study area contains metavolcanic (i.e., meta-acidic) and metavolcanoclastic( i.e., felsic meta-volcanic breccia) rocks which belong to the Tsaliet Group; Phanerozoic formations such as Enticho sandstone, Adigrat sandstone and Edaga Arbi Glacials which are part of the Tambien Group; felsic sub intrusive; granite, and phyllite(i.e., spotty micaceous and quartzo-feldspathic) rock units. The largest part of the study area is covered by the MV and MVC rock units followed by the granite rock unit. The phyllite unit of the study area is not part of either the meta-volcanic or the meta-sedimentary units. It is rather an intervening zone between these two main units. Depending on the field structural data analysis, the rock out crops of the study area has three phases of deformation. These are:- (i) the first or earlier phase of deformation(D1), (ii) the Second phase of deformation(D2), and (iii) the third phase of deformation(D3). D1 is associated with folding of primary bedding and appearance of tight to isoclinal minor folds, persistent foliation (S1), and linear fabrics defined by platy minerals. D2 is related to N-S trending upright, open folds and crenulation lineations with sub horizontal fold axes without producing a pervasive foliation. D3 is recognized by brittle structures like reverse faults, quartz veins and joints. Based on the petrographic study, the out crop units of the study area are dominated by index minerals such as chlorite, albite, epidote, muscovite, biotite, calcite and hornblende. These minerals indicate low grade metamorphism and this particularly belongs to the lower greenschist facies. The time relationship between metamorphism and deformation of the rock units of the study area are formed between the two tectonic events D1and D2 and hence they are called late or inter-tectonic.



Pan-African Orogeny, Neoproterozoic, Arabian Nubian Shield, Megab- Hawzien Area, Metavolcanic Rocks, Metavolcanoclastic Rocks, Phyllite, Petrography, Metamorphism, Deformation, Structures, Porphyroblasts