40Ar/ 39Ar dating of 1.0-1.1 Ga magnetizations from the Sa∼o Francisco and Kalahari cratons: tectonic implications for Pan-African and Brasiliano mobile belts

Paleomagnetic poles from 1.1-1.0 Ga dyke swarms in eastern Brazil (Sa∼o Francisco Craton) are compared with 1.0 Ga poles from granulites of the Namaqua Province in southern Africa (Kalahari Graton). The intrusive ages of dykes are estimated from ⁴⁰Ar/ ³⁹Ar dating of outgassed biotites from baked country rocks. The age of magnetization for the granulites is derived by combining ⁴⁰Ar/ ³⁹Ar hornblende and biotite dates. When restored to a Mesozoic pre-drift configuration the paleomagnetic poles are in crude spatial agreement but are temporally discordant. To satisfy both paleomagnetic and geochronologic constraints, a reconstruction involving separation of the Sa∼o Francisco and Kalahari cratons is required, indicating that the intervening Pan-African (Brasiliano) mobile belt may record a craton-craton collision.