Academia Brasileira de Ciencia:CAIXA Postal 229, 20001 Rio de Janeiro Brazil da t. 13, no. 3 (set. 30, 1941)cambio editore
Abstract
Metabasite intercalations in Precambrian metasedimentary sequences from Namibe Province, southwestern Angola, show strong geochemical affinity with komatiites and komatiitic basalts. Rb-Sr systematics, probably "perturbed" by polymetamorphic processes, as well as by crustal contamination and alteration, seem to indicate two main thermal events, at 2.0 Ga (initial 87Sr/86Sr = 0.70194) and 0.9 Ga (initial 87Sr/86Sr = 0.70614), respectively, roughly corresponding to the Early Proterozoic (Eburnean) cratonization, and to the beginning of the Pan-African event. However, Sm-Nd isotopic data display an errorchron of 3.1±0.1 Ga (initial 143Nd/144Nd = 0.50868) consistent with the values inferred by both DM (depleted mantle: 3.4±0.3 Ga) and CHUR (chondritic mantle: 3.2±0.4 Ga) model ages, suggesting an of Early middle Archean magmatism in SW-Angola
