Geological Structures and Tectonic Evolution of the Neoproterozoic Terrain of Guwila Area, Tigrai, Northern Ethiopia
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Date
2014-05-05
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Addis Ababa University
Abstract
Precambrian rocks out cropping in the Guwila area fall under two major groups, the metasedimentary and metavolcanic groups. The metasediments are part of the Tambien Group and the metavolcanic rocks are part of the Tsaliet Groups, both of which occur extensively in the region. Phyllites in the study area have a sedimentary origin and hence they can be grouped under the metasedimentary rocks along with other units such as slate, dolomite, and limestone. The metabasites and metavolcanic breccias, on the other hand, constitute the Tsaliet metavolcanics. The metasedimentary rocks are the predominant units in the Guwila area. The rock units generally trend in the NE and dip NW. However changes in the dipping direction of foliation is noticed in some of the areas and the structural analysis based on field observation and streoplot revealed the presence of locally developed antiforms and synforms on the central part of the study area. Similar to most of the Neoproterozoic units in the northern part of Ethiopia, the rocks in the Guwila area are metamorphosed under a low grade greenschist facies; some of the units still preserve the original texture at mesoscopic and microscopic scales such as primary bedding in the metasedimentary rocks. Relict plagioclase minerals being replaced by calcite and sericite and presence of muscovite, chlorite, and epidote all indicate low grade metamorphism. At least two phases of ductile deformation are observed on the area. North-south directed deformation which resulted in the formation of F1 tight to isoclinals folds with steeply plunging fold axis is regarded as the first phase deformation. It is also responsible for the development of the regional foliation. Second phase is related to a N-S trending nearly horizontal folds with larger interlimb angle and the formation of crenulation lineation and also crenulation cleavage.
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Geological Structures, Tectonic Evolution, Neoproterozoic Terrain, Guwila Area, Tigrai, Northern Ethiopia