Paleomagnetism of the Lesotho basalt, southern Africa

Paleomagnetic study of four sections from Middle Jurassic Karoo lava, located in Lesotho and South Africa, yielded a new paleomagnetic pole for Africa with coordinates 71.6°N, 273.5°E (A95 = 3.7°, K = 33, N = 47). Paleosecular variation, estimated as the angular standard deviation of VGPs distribution is 14.1° (+ 2.4°− 1.8°), which is considerably lower than expected for this time interval and latitudinal band. Preliminary paleointensity results indicate a low field intensity during the acquisition of the magnetization, this new result tends to support a possible correlation between secular variation and dipole intensity. When the lower to middle Jurassic paleomagnetic data set for Africa is considered, a difference of 13.9 ± 8.7° of arc is found to exist between the mean Northwest and South African poles. Furthermore, while the Northwest African pole is in very good agreement with the lower to middle Jurassic North American pole, whichever set of rotation parameters is used to close the North Atlantic ocean, the South African pole falls some 12–15° of arc apart. As intraplate deformation models, developed to achieve tighter fit of West Gondwana prior to the opening of the South Atlantic, fail to account fully for the difference between Northwest and South African poles, the pre-Cretaceous Apparent Polar Wander Path for Africa has to be considered with caution.