The paleomagnetism of the ring complexes at Marangudzi and the Mateke Hills

Oriented rock cores have been drilled at nineteen sites in four intrusive ring complexes in the Nuanetsi igneous province of southeastern Southern Rhodesia. At Marangudzi eleven sites were distributed among nine rock types; the aim was to investigate the relation between rock type and remanent magnetization. Six of these sites, and one from another complex, gave no paleomagnetic results. At ten sites stable components of remanent magnetization, which remained after partial demagnetization in alternating fields, gave closely grouped directions approximately reversed with respect to the present geomagnetic field. These directions are considered to be those of thermoremanent magnetizations acquired when the rocks were intruded. The mean north paleomagnetic pole position from these ten sites is 60.9°S, 86.2°E, and A95 = 6.5°. Samples from Marangudzi have been dated from K-Ar decay at close to 190 m.y., and it is probable that the other complexes are of approximately the same age. Two sites in different complexes are normally magnetized, which suggests that the geomagnetic field changed sense from reversed to normal near the close of the intrusive episode. Evidence is presented which shows that relative movement between Africa and the pole was small during the Mesozoic era.