The Puduhush gabbro in Griqualand West, South Africa: extending ca. 1.89 to 1.83 Ga intraplate magmatism across the proto-Kalahari Craton

Abstract

The Puduhush gabbro is located on the western margin of the proto-Kalahari Craton in Southern Africa. This gabbro intrudes the Volop Formation, which conformably overlies the Hartley Formation lava of the late Palaeoproterozoic Olifantshoek Group. Here we report a new U-Pb ID-TIMS baddeleyite age as well as petrographic, whole-rock geochemical and palaeomagnetic results for the Puduhush gabbro. The gabbro shows a well-preserved sub-ophitic texture between clinopyroxene and plagioclase, with minor amounts of amphibole, olivine, biotite and Fe-Ti oxides. The new U-Pb ID-TIMS baddeleyite age of 1 881 ± 1 Ma reported here for the Puduhush gabbro, together with existing ages for the Hartley Formation, define a ca.1 916 to 1 881 Ma age bracket for the Volop Formation. Our 1 881 ± 1 Ma age is also within error of ages reported for the oldest episode (so-called Episode 1) of the ca.1.89 to 1.83 Ga magmatism in the eastern and northern parts of the proto-Kalahari Craton. Our geochemical results also suggest compositional similarities between the Puduhush gabbro and Episode 1 magmatism, particularly the post-Waterberg sills. The virtual geomagnetic pole calculated here for the Puduhush gabbro (VGP: 1.6°N; 352.0°E; A95 = 14.2°) is consistent with the Episode 1 pole. All data are therefore combined to produce a new palaeomagnetic pole (11.7°N; 8.8°E, A95 = 9.3°) for Episode 1 magmatism. The present study provides the first evidence that the ca.1.89 to 1.83 Ga magmatism had a wider footprint that previously thought, extending to the western margin of the proto-Kalahari Craton. This wide-scale magmatism, previously proposed to be related to a back-arc extension setting, is here reinterpreted in the context of a mantle plume. Our results are consistent with the lithostratigraphic-based notion that at least parts of the red-bed successions (i.e., Olifantshoek and Waterberg Groups) that are hosts to the ca.1.89 to 1.83 Ga magmatism could be correlative units, representing an extensive sedimentary sequence that once covered large expanses of the proto-Kalahari Craton.