Geochemistry, PbPb single zircon ages and NdSr isotope composition of Precambrian rocks from southern and eastern Ethiopia: implications for crustal evolution in East Africa

摘要: Abstract Geochemical and isotope data for granitoid rocks from southern eastern Ethiopia delineate the presumed margin of Pan-African juvenile terrain Arabian-Nubian Shield against an older crustal segment unknown origin extending to northern Somalia. Granitoids have higher Na2O Na 2 0 K O lower Cr Ni than granitoids with comparable SiO2 values Ethiopia. In three periods magmatism are identified on basis single zircon 207 Pb 206 evaporation ages, namely at ∼850, ∼750-700 ∼650-550 Ma, these correlate well events documented other parts Shield. The initial ϵNd(700 Ma) ϵsr(700 range −1.2 +3.2 −13.4 + 3.7, respectively, which precludes any significant contribution much continental crust in generation rocks. Neodymium mean residence based a depleted mantle model, 0.96 1.26 Ga. These support interpretation that constitutes part contrast, show geochemical features S-type granites. Pal aeo-Neoproterozoic ages (781–2489 found. Initial from−4.3 −18.3 33.3 99.8, respectively. 1.62 2.88 data, comparison western Ethiopia, indicative considerable reworking pre-Pan-African crust. Variations age, SrNd ratios chemistry regional scale also suggest existence two separate basement terrains between may be separated by tectonic line now concealed Phanerozoic This represent major boundary west gneissic east, thus delineating