Abstract
The Hartley Basalt Formation in the Northern Cape of South Africa comprises dominant Fe rich tholeiitic basalt and tuff, with porphyritic andesite found at only one locality. Geological evidence points to a rift-related setting which evolved into a passive continental margin as the early Kaapvaal Craton was split up. This marks a change in the stratigraphical record of the Archaean Kaapvaal Craton, from successively larger Witwatersrand, Ventersdorp and Transvaal intracratonic basins, to localised Waterberg Rifts, following the 2050 Ma Bushveld event. These Waterberg rifts are the earliest feature on the craton which can plausibly be related to a plate tectonic Wilson Cycle. The Hartley Formation now crops out within a linear mountain belt, formed at the end of the Wilson Cycle as rocks of the Kheis Tectonic Province overthrust the Archaean Kaapvaal Province along the Kheis Front. Variable degrees of low grade metamorphism are seen in samples from different localities. A 1928 ± 4 Ma PbPb age by the Kober method on clear magmatic zircons from a porphyry sample is consistent with, and represents a substantial refinement of, the 1984 ± 78 Ma RbSr isochron age for the Hartley basalts. This is the most precise age determination for a rock formed in any of the Waterberg basins. Ancient Pb loss from large zircons after 1906 Ma is thought to represent a maximum age for Kheis metamorphism. A 1750 ± 60 Ma RbSr biotite age on a dolerite postdates the Kheis deformation in the foreland region and is a minimum age for the end of the Kheis Wilson Cycle.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.