Ayalew, Dereje (Professor)Zafu, Amdemichael2018-06-292023-11-092018-06-292023-11-092016-07http://10.90.10.223:4000/handle/123456789/4852Boko magmatic complex is situated in transitional zone between Central and Northern MER segments. The area is located approximately 92.02 Km from Addis Ababa. The main objective of the research study is to understand the magmatic evolution and the extent of the main collapse zone of the complex. To meet the objectives, starting from the beginning different methods have been applied. The methods are; remote sensing, field observation, petrography, structural data analysis, geochemistry and soil CO2 degassing. The Boko magmatic complex is characterized by two main phase of eruption; Boko caldera forming eruptive activity and post caldera eruptive activity. These episodes give volcanic products that constitute the complex. The major volcanic units are rhyolitic lava flow, pumice flow, ignimbrite, lower pumice fall, rhyolitic lava dome, obsidian, lower basalt, upper ash flow, scoria and upper basalt. The surface thermal manifestation and anomalous CO2 degassing suggests Boko has currently active volcanic activity beneath the volcano. The volcanic products are affected by extensional tectonics which is manifested by appearance of geological structures like, joint and NNE-SSW trending major normal faults. The geochemical analysis results indicates the Boko rocks are bimodal in composition, mafic and silicic, lacking intermediate composition. The mafic rocks are transitional to weakly subalkaline basalt and the silicic rocks are dominantly peralkaline rhyolites. The two groups of rocks are co-genetic and related to each other by fractional crystallization process starting from mantle-derived basaltic magma with slight crustal material involvement. The soil CO2 degassing measurement result shows that it has biogenic and volcanic-hydrothermal source. The total flux from the two sources is 74.71 t d-1. The mean of CO2 flux from the biogenic source is 0.041 g m-2 d-1 and from volcanic-hydrothermal origin is 2.14 g m-2 d-1. The combination of remote sensing, soil CO2 flux value distribution, field observations and structural data analysis suggest the main collapse zone of Boko Caldera has elliptical geometry with a dimension of 6 Km (E-W) by 4 Km. The major caldera axis is along E-W which is in agreement with the Main Ethiopian Rift regional stress direction. Key words: Boko Magmatic Complex, Fractional crystallization, Crustal contamination, CO2 degassing, Caldera forming eruption, Caldera collapse and Main collapse areaenBoko Magmatic ComplexFractional crystallizationCrustal contaminationCO2 degassingCaldera forming eruptionCaldera collapse and Main collapse areaThesis