Twelve Rb-Sr whole-rock analyses are reported for two neighbouring monzogranites near Jato Aka in south-eastern Nigeria. Nine data points yield a whole-rock isochron of 511 ± 32 Ma with an initial 87Sr/86Sr ratio of 0.70910 ± 0.00031 (87Rb decay constant of 1.42 × 10−11 a−1; MSWD = 0.4). These results are interpreted as showing that the two plutonic bodies were emplaced at about 511 Ma ago and that older crustal matter was a constituent of the magma. Available data indicate that Pan-African magmatic activity in the eastern parts of Nigeria waned about 511 Ma ago with the emplacement of Jato Aka monzogranites.
12/1983; 1(3-4):339-342. DOI:10.1016/S0731-7247(83)80020-2