Geological mapping report of area A, Igayaza, Isingiro Dstrict.
Abstract
The geological mapping exercise was carried in Gayaza synclinorium of Karagwe-Ankolean system which is located in Isingiro District estimated to be 31 km south of Mbarara city. The major aim of the training is to equip geologists and geoscientists with a variety of skills in geologic mapping that is identification of rock types in a given area, by various mapping methods such as following contacts, vegetation cover and many others. In turn, geologists and geoscientists can use such acquired skills in various fields like petroleum exploration.
The Karagwe-Ankolean system(1400 & 95 Ma) is exposed in Uganda, as the Northern-most extension of the Kibaran mobile belt, extending from Angola further South to Uganda in the North (Nakajjigo, 2021). It is said to terminate into the Buganda-Toro system(older) which is itself overlying the Basement Complex. Distinguishing B-T from the Basement Complex rocks is, however, difficult.
The geotectonic evolution of the Kibaran belt involved predominantly extensional and compressional regimes and the stratigraphic successions and correlation for the rocks of the Kibaran Belt is not simple, because of the complex folding and refolding due to granitic intrusions, which in most places overturned the sequence. There are also no known fossils to be used in identification and correlation of these Precambrian systems. Acid gneisses, migmatites, folded metasediments of originally predominantly argillaceous composition intercalated with arenaceous horizons and conglomeratic basal members, rarely calcareous and volcanic sequences are predominating rock units and are seen intruded by biotite granites (G1-G4), pegmatites, and hydrothermal veins of acid and basic dykes (Placeholder2)
The mapped area includes major structures such as; bedding, faults, folds and joints all exhibiting two major trends; the northwest-southeast (NW-SE) trend which is similar to that of the regional folds and the northeast-southwest (NE-SW) direction similar to that of the cross folds. The minor structures include; micro-folds, micro-faults, quartz veins, boudinage, foliation and lamination. Analysis of the structures includes taking measurements such dip, strike, plunge angles (in case of folds) and relating this to petroleum potential of the area.
The K-A system sedimentation started after the lower Proterozoic and related orogenies around 1900 Ma and after 2100 Ma and before 1800 Ma and ceased with the Kibaran orogeny at 1250-1300 Ma. It formed an important East-Northeast structural trend along which tectonic or igneous activity continued intermittently till the Pan African event at about 500 Ma according to Clifford, 1970.