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.
Four unconformity-bound sequences can be identified in the Purana successions in southern India, of which the third sequence (Sequence III) has the widest distribution. Sequence III contains deep-water carbonate units with consistent sedimentological characteristics across the subcontinent. The current extent of field relationships and existing ages has not allowed the correlation and chronology of these carbonates to be established conclusively. Palaeomagnetism may help resolve this essential question for the Purana sedimentation. Here, we report new palaeomagnetic results (HIG+/– pole: 21.7° N, 81.1° E, radius of cone of 95% confidence A95 = 15.9°) from Sequence III carbonates in the Kaladgi (Badami Group) and Bhima (Bhima Group) basins. The HIG+/– magnetization, revealed after the removal of secondary magnetizations that include a present-day field and an Ediacaran–Cambrian overprint, is interpreted to be primary based on its dissimilarity to known younger magnetizations, the presence of distinctly different magnetic components in sites and a positive reversal test. Our HIG+/– pole differs from the c. 1.4 Ga pole and various c. 1.1 Ga and younger poles. Instead, it overlaps with the Harohalli dyke pole that was long considered to be c. 823 Ma in age, but has recently been suggested to be much older with an age of c. 1192 Ma. We therefore consider the uppermost carbonate beds of Badami and Bhima groups to have been deposited during late Mesoproterozoic times. A critical evaluation of parameters from which an earlier Neoproterozoic age for these carbonates was established indicates that the available 40Ar/39Ar, Rb–Sr and U–Pb ages in the Kaladgi and Bhima basins could reflect the timing of post-depositional alteration events.
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