Large-scale liquid immiscibility at the top of the Bushveld Complex, South Africa

Abstract

Research Article| June 01, 2012 Large-scale liquid immiscibility at the top of the Bushveld Complex, South Africa J.A. VanTongeren; J.A. VanTongeren 1Yale University, Kline Geological Laboratory, New Haven, Connecticut 06520, USA2American Museum of Natural History, 79th and Central Park West, New York, New York 10024, USA Search for other works by this author on: GSW Google Scholar E.A. Mathez E.A. Mathez 2American Museum of Natural History, 79th and Central Park West, New York, New York 10024, USA Search for other works by this author on: GSW Google Scholar Geology (2012) 40 (6): 491–494. https://doi.org/10.1130/G32980.1 Article history received: 28 Oct 2011 rev-recd: 03 Jan 2012 accepted: 09 Jan 2012 first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation J.A. VanTongeren, E.A. Mathez; Large-scale liquid immiscibility at the top of the Bushveld Complex, South Africa. Geology 2012;; 40 (6): 491–494. doi: https://doi.org/10.1130/G32980.1 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 Detailed study of the top 625 m of the Bushveld Complex (South Africa) suggests that the magma developed a siliceous cap generated by liquid immiscibility. The lower ∼300 m of this section, which consists of magnetite-bearing ferrodiorite with several magnetite-rich layers, contains cumulus apatite with relatively low rare earth element (REE) concentrations and no chondrite-normalized Eu anomaly. In contrast, apatite in the overlying 325 m thick portion of the section has three times higher REE concentrations and a negative Eu anomaly, and the cumulate rocks contain cumulus orthoclase and quartz. The contact between the two parts of the section occurs over a limited stratigraphic range (<50 m). Large-scale silicate liquid immiscibility resulting in the physical separation of a dense, Fe-rich magma to form the lower part of the sequence and a buoyant Si-rich magma to form the upper part of the sequence is best able to explain the observations. In addition, the phases in the upper siliceous cap of the Bushveld Complex are in major and trace element equilibrium with portions of the overlying Rooiberg rhyolites and/or Rashoop granophyres, consistent with these rocks having originated as residual liquids after extensive fractional crystallization of the Bushveld magmas. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.