U–Pb geochronology and paleomagnetism of the Westerberg Sill Suite, Kaapvaal Craton : Support for a coherent Kaapvaal–Pilbara Block (Vaalbara) into the Paleoproterozoic?

• Published in: Precambrian Research
• Main Authors: Kampmann, Tobias Christoph, Gumsley, Ashley Paul, de Kock, Michiel Olivier, Söderlund, Ulf
• Format: Article in Journal/Newspaper
• Language: English
• Published: Lund University 2015
• Subjects: Apparent polar wander path; Baddeleyite U–Pb geochronology; Kaapvaal; Paleomagnetism; Paleoreconstruction; Vaalbara; Geology; Geologi; Geomagnetic Pole
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-6229; https://doi.org/10.1016/j.precamres.2015.08.011

Precise geochronology, combined with paleomagnetism on mafic intrusions, provides first-order information for paleoreconstruction of crustal blocks, revealing the history of supercontinental formation and break-up. These techniques are used here to further constrain the apparent polar wander path of the Kaapvaal Craton across the Neoarchean–Paleoproterozoic boundary. U–Pb baddeleyite ages of 2441 ± 6 Ma and 2426 ± 1 Ma for a suite of mafic sills located on the western Kaapvaal Craton in South Africa (herein named the Westerberg Sill Suite), manifests a new event of magmatism within the Kaapvaal Craton of southern Africa. These ages fall within a ca. 450 Myr temporal gap in the paleomagnetic record between 2.66 and 2.22 Ga on the craton. Our older Westerberg Suite age is broadly coeval with the Woongarra magmatic event on the Pilbara Craton in Western Australia. In addition, the Westerberg Suite on the Kaapvaal Craton intrudes a remarkably similar Archean-Proterozoic sedimentary succession to that on the Pilbara Craton, supporting a stratigraphic correlation between Kaapvaal and Pilbara (i.e., Vaalbara). The broadly coeval Westerberg–Woongarra igneous event may represent a Large Igneous Province. The paleomagnetic results are more ambiguous, with several different possibilities existing. A Virtual Geomagnetic Pole obtained from four sites on the Westerberg sills is 18.9°N, 285.0°E, A95 = 14.1°, K = 43.4 (Sample based VGP, n = 34: 16.8°N, 2879.9°E, dp = 4.4°, dm = 7.7°). If primary (i.e., 2441–2426 Ma), it would provide a further magmatic event within a large temporal gap in the Kaapvaal Craton's Paleoproterozoic apparent polar wander path. It would suggest a relatively stationary Kaapvaal Craton between 2.44 Ga and 2.22 Ga, and ca. 35° of latitudinal drift of the craton between ca. 2.66 Ga and 2.44 Ga. This is not observed for the Pilbara Craton, suggesting breakup of Vaalbara before ca. 2.44 Ga. However, it is likely that the Woongarra paleopole represents a magnetic overprint acquired during the Ophtalmian or ...