Cooling of the Bushveld Complex, South Africa: Implications for paleomagnetic reversals

Abstract

Research Article| June 01, 2013 Cooling of the Bushveld Complex, South Africa: Implications for paleomagnetic reversals R. Grant Cawthorn; R. Grant Cawthorn * School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, South Africa *E-mail: Grant.cawthorn@wits.ac.za. Search for other works by this author on: GSW Google Scholar Susan J. Webb Susan J. Webb School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, South Africa Search for other works by this author on: GSW Google Scholar Author and Article Information R. Grant Cawthorn * School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, South Africa Susan J. Webb School of Geosciences, University of the Witwatersrand, Private Bag 3, 2050 Wits, South Africa *E-mail: Grant.cawthorn@wits.ac.za. Publisher: Geological Society of America Received: 11 Sep 2012 Revision Received: 14 Jan 2013 Accepted: 20 Jan 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2013 Geological Society of America Geology (2013) 41 (6): 687–690. https://doi.org/10.1130/G34033.1 Article history Received: 11 Sep 2012 Revision Received: 14 Jan 2013 Accepted: 20 Jan 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R. Grant Cawthorn, Susan J. Webb; Cooling of the Bushveld Complex, South Africa: Implications for paleomagnetic reversals. Geology 2013;; 41 (6): 687–690. doi: https://doi.org/10.1130/G34033.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Igneous rocks record the direction of the Earth’s magnetic field as they cool through their Curie temperature. The mafic magmas of the 8-km-thick Bushveld Complex of South Africa took 65 k.y. to be emplaced, 180 k.y. to solidify (to 900 °C), and a further 500 k.y. for the entire intrusion to cool below 580 °C, the Curie temperature of magnetite. Once solid, the cooling of this intrusion occurred mainly from the top downward, with slower cooling through its floor. As a result, the upper rocks cooled through their Curie temperature before those at the base; the portion 6 km below the upper contact was the last to reach the Curie temperature. Thus, the intrusion records a mainly top-down sequence of three paleomagnetic reversals starting with N (normal direction). The last two are also recorded from the base of the mafic sequence upward as it cooled through 580 °C later than the top. The lateral variations in thickness of the Bushveld Complex are important in this interpretation, because thinner sections cooled more quickly. Hence, reversals do not always correlate with stratigraphy. Specific reversals provide a cooling marker horizon that may crosscut the stratigraphic layering. The interpretation of the order and number of paleomagnetic reversals presented here differs from previous interpretations that envisage the oldest paleomagnetic directions to be recorded sequentially from the base upward, and has implications for the interpretation of paleomagnetic results from all thick intrusions, mafic and felsic. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.