Deformation History and Geochemistry of Neoproterozoic Rocks of Tahtailogomti Area, Tigrai, Northern Ethiopia
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Date
2018-05-25
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Addis Ababa University
Abstract
The Tahtai Logomti area is dominated by the Neoproterozoic basement rocks of Northern Ethiopia, occurred between the Adwa and Mai Kenetal blocks and covered by metavolcano-sedimentary rocks which belong to the Tambien and Tsaliet Groups and are part of the Arabian Nubian Shield. In this study, the integrated petrographic, structural and geochemical analyses were used to understand the metamorphism, deformation history and paleo-tectonic setting of the area. Basic to acidic metavolcanic, basic to intermediate metavolcanoclastic, meta-agglomerate and metatuff rock units characterized in the Tsaliet Group, whereas lower slate, lower metalimestone, upper slate and upper metalimestone are part of the Tambien Group. The quartz veins and acidic dike that has different orientations cut the metavolcani/clastic and metasedimentary rock units. Most of the units of the study area are characterized by volcanic origin parent rocks. The field observation lithologies, structural and petrographic interpretation of the rocks show that the area was affected by lower greenschist facies metamorphism. The macro and microstructures identification and analysis show that the study area has been affected by at least three events of deformation: D1 and D2 ductile deformations and a later brittle phase of deformation (D3). The relationship between metamorphism and deformation can be recognized from the mineral assemblages and micro structural features in the petrographic part. The first event of deformation (D1) shows NE striking S1 foliation and M1 metamorphic event and also pencil structure. It is represented by the development of mineral assemblages such as chlorite, actinolite, epidote, muscovite/sericite, plagioclase, calcite and recrystallized quartz. The second event of deformation is responsible for the development of low plunging folds, kink band folds and en echelon array veins. However, the third phase deformation (D3) is related to a different set of joints and faults that cut the regional foliation (S1) throughout each rock units. The geochemical data plotted on different tectonic discrimination diagrams clearly indicates that the metavolcanic rocks of Tahtai Logomti area are characterized by calc-alkaline magma type and they were erupted in the volcanic arc setting. The general petrological and geochemical characteristics of the Tahtai Logomti metavolcanic rocks provides an important evidence to consider the area as part of the subduction-related arc accretion of the ANS.
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Deformation, Foliation, Metamorphism, Metavolcanic, Neoproterozoic