Palaeomagnetism of the early Palaeoproterozoic, volcanic Hekpoort Formation (Transvaal Supergroup) of the Kaapvaal craton, South Africa

The Kaapvaal craton (South Africa) was the host of several major magmatic events during the Palaeoproterozoic, including the volcanic Hekpoort and Ongeluk Formations. Their possible comagmatic origin is the subject of a long debate. We performed a palaeomagnetic study of the Hekpoort Formation to be compared with the available palaeopole of the Ongeluk Formation, but also to contribute to the apparent polar wander path of the Kaapvaal craton. Characterization of magnetic mineralogy by three-axis thermal demagnetization of isothermal remanent magnetization and magnetic susceptibility versus temperature points out magnetite as the main remanence carrier in most samples. Five magnetic components were identified in total, of which the least stable (HKE) near parallels the present geomagnetic field. At higher levels of demagnetization (above 400 °C), two components (HKD and HKC) are identified as thermoviscous overprints likely related to the Karoo large igneous province (LIP) and a magmatic event which occurred between the emplacement of the ∼2055 Ma Bushveld Complex and HKD (possibly linked to the Umkondo LIP), respectively. This LIP is known to be associated with extensive remagnetization. The second most stable component HKB was also revealed at higher steps of thermal and alternative-field treatment. The HKB palaeopole (latitude = 28.4°N and longitude = 54°E) is similar to those reported from the Bushveld Complex (∼2055 Ma) and the Vredefort impact structure (∼2023 Ma). A potentially primary remanence direction (HKA; declination = 337°, inclination = 80° and α = 6.2°) was identified in most sites during the highest levels of thermal demagnetization. Note that the HKA pole position (latitude = -44°N and longitude = 40°E) is significantly different from the palaeopole for the Ongeluk Formation (latitude = -0.5°N and longitude = 107°E). Although, the primary nature of HKA is supported by positive fold and reversal tests, we cannot exclude the possibility that this component represents an overprint. HKA is, however, most likely older than ∼2.0 Ga given its anteriority to HKB components.