Paleomagnetism of a Neoarchean-Paleoproterozoic carbonate ramp and carbonate platform succession (Transvaal Supergroup) from surface outcrop and drill core, Griqualand West region, South Africa

摘要

Detailed paleomagnetic study across the Archean-Paleoproterozoic boundary interval preserved in the Ghaap Group, Transvaal Supergroup, of the Kaapvaal craton reveals a complex series of viscous and thermo-chemical magnetic overprints. Despite this complex history, a potential primary single-polarity remanence direction was revealed at high-temperature demagnetization steps in about 10% of orientated drill core samples only. This component (declination = 132 degrees, inclination = 69 degrees) was not identified in any of the outcrop sites. Overprint directions include a present geomagnetic field remanence and a very well developed thermo-chemical overprint (declination = 359 degrees, inclination = 54 degrees), which is believed to be associated with a similar to 2.0 Ga regional thermal event and the development of extensive epigenetic Pb-Zn deposits. At higher levels of demagnetization, two shallow west-directed components appear to be related to the extrusion of the Ongeluk Formation lava at 2.22 Ga (declination = 268 degrees, inclination = -20 degrees; eastern parts of the studied region) and to the post-1.92 Ga Kheis orogeny (declination = 272 degrees, inclination = 16 degrees; exclusive to the western margin of the study area), respectively. (c) 2008 Elsevier B.V. All rights reserved.