Rb-Sr and K-Ar age measurements on the Great Dyke of Southern Rhodesia

Rb-Sr and K-Ar ages of minerals and Rb-Sr ages of total-rock samples from the Great Dyke of Southern Rhodesia are reported. The agreement of Rb-Sr and K-Ar ages on two biotites establishes a lower limit of 2530±30 m.y. for the age of the Dyke and shows that it is significantly older than the Bushveld complex. The K-Ar data on one plagioclase indicates that the age of emplacement may be as great as 2800 m.y., and this is not inconsistent with the total-rock data. A primary Sr87/Sr86 ratio of 0.7010±.0019 is obtained from the total-rock samples.