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U-Pb geochronology and paleomagnetism of the Westerberg Sill Suite, Kaapvaal Craton – support for a coherent Kaapvaal–Pilbara Block (Vaalbara) into the Paleoproterozoic?
Lund University.ORCID iD: 0000-0003-1867-2342
Lund University.
University of Johannesburg.
Department of Geology, GeoBiosphere Science Centre, Lund University, Lund University.
2015 (English)In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 269, p. 58-72Article in journal (Refereed) Published
Abstract [en]

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 Capricorn Orogeny, invalidating a paleomagnetic comparison with the Westerberg Sill Suite. Alternatively, our Westerberg Virtual Geographic Pole manifests a 2.22 Ga magnetic overprint related to Ongeluk volcanism. The similarity between Ongeluk and Westerberg paleopoles however may also infer magmatic connections if both are primary directions, despite the apparent 200 million year age this difference.

Abstract [en]

Precise geochronology, combined with paleomagnetism of mafic intrusions, provides first-order information necessary for paleoreconstruction of crustal blocks, and for revealing the history of supercontinent formation and break-up. These techniques are used here to further constrain the apparent polar wander path of the Kaapvaal Craton through the Neoarchean and Paleoproterozoic. U-Pb baddeleyite ages of 2441 ± 6 Ma and 2426 ± 1 Ma for a suite of sills located on the western Kaapvaal Craton in South Africa (named here the Westerberg Sill Suite), manifests a new event of mafic magmatism within the Kaapvaal Craton of southern Africa. These ages fall within a ca. 450 Ma gap in the paleomagnetic record between 2.66 and 2.22 Ga. In addition, our older Westerberg Suite age is coeval with the felsic portions of the Woongarra magmatic event on the Pilbara Craton in Western Australia. The Westerberg Suite intrudes into a remarkably similar Archean-Proterozoic sedimentary succession, hence supporting a stratigraphic correlation between Kaapvaal and Pilbara (i.e., Vaalbara). The 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 48.9 °N, 258.0 °E, α95 = 14.1, K = 43.4). If primary (i.e., 2441 to 2426 Ma), it would provide a further magmatic event that would fit well into a large 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. 2.7 Ga and 2.44 Ga. This is not seen for the Pilbara Craton, suggesting breakup of Vaalbara before ca. 2.44 Ga. It is however more likely that the Woongarra volcanics paleopole represents a magnetic overprint acquired during either the Ophtalmian or Capricorn Orogeny, thus disallowing a paleomagnetic comparison with the Westerberg Sill Suite. Alternatively, our Westerberg Virtual Geographic Pole manifests a 2.22 billion year old magnetic overprint related to Ongeluk volcanism. The similarity between Ongeluk and Westerberg paleopoles however may also infer magmatic connections if both are primary, despite the 200 million years age difference. Further geochronology on the Ongeluk volcanics would be needed to validate such arguments.

Place, publisher, year, edition, pages
2015. Vol. 269, p. 58-72
Keyword [en]
Apparent polar wander path, Baddeleyite U–Pb geochronology, Kaapvaal, Paleomagnetism, Paleoreconstruction, Vaalbara, Earth sciences - Endogenous eartn sciences
Keyword [sv]
Geovetenskap - Endogen geovetenskap
National Category
Geology
Identifiers
URN: urn:nbn:se:ltu:diva-6229DOI: 10.1016/j.precamres.2015.08.011Local ID: 46dff7f4-5380-4889-8597-5b94cd7593bdOAI: oai:DiVA.org:ltu-6229DiVA: diva2:979106
Note
Upprättat; 2015; 20150212 (tobkam)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved

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