Stratigraphy and petrography of the Hartley Basalt Formation: northern Cape Province ( South Africa).
The Hartley Basalt Formation crops out close to the W margin of the Kaapvaal Craton in the N Cape Province. It is characterized by original basalt lava flows and pyroclastic fragments mixed with quartz arenite, with minor conglomerate and rare quartz-feldspar porphyry. The Hartley Formation originated as the result of basaltic eruptions during the deposition of a thick quartz arenite sequence near the margin of a fault-bounded basin. Explosive volcanism led to the intimate mixing of unconsolidated sands which originally underlay the Hartley Formation with basaltic material to form the tuffaceous quartz arenite to welded tuff suite exposed near the top of Hartley Hill. A plate tectonic model is proposed which relates the origin of the Hartley Basalt Formation and Groblershoop Sequence to a mid-Proterozoic splitting of the Kaapvaal Craton, and the development of an ocean basin in the present Kheis-Rheoboth Province, while the Waterberg and Soutpansberg Groups formed in an aulocogen along the failed arm of a triple junction. -from Author