Old, strong continental lithosphere with weak Archaean margin at approximately 1.8 Ga, Kaapvaal Craton, South Africa
Old, strong continental lithosphere with weak Archaean margin at approximately 1.8 Ga, Kaapvaal Craton, South Africa (in Kaapvaal Craton, Maarten J. de Wit (editor), Stephen H. Richardson (editor) and Lewis D. Ashwal (editor))
South African Journal of Geology (June 2004) 107 (1-2): 255-260
Low elastic strength of ancient lithosphere based on flexural analyses has been interpreted to reflect elevated regional geothermal gradients in response to higher global heat production in the past. Here we present a flexural analysis of Archean/Palaeoproterozoic sediment cover along the western margin of the Archean Kaapvaal craton based on seismic stratigraphy. Our results show that between approximately 1.93 and approximately 1.75 Ga, the Archaean margin of the craton had an effective elastic thickness of 7.5 to 10 km compared to its present day value of 60 to 70 km. Because the Kaapvaal craton had already stabilized by approximately 2.7 Ga and was underlain by 150 to 300 km thick strong mantle lithosphere, it is unlikely that the relatively thin elastic thickness along this old margin reflects a change in secular cooling of the Earth. Instead, we interpret the low elastic strength to be a transient marginal tectonic effect similar to that recorded along modern continental margins.