The age of the Koegel Fontein anorogenic complex, South Africa, and its relationship to the regional timing of magmatism and breakup along the South Atlantic rifted margin
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Research Article| March 01, 2019 The age of the Koegel Fontein anorogenic complex, South Africa, and its relationship to the regional timing of magmatism and breakup along the South Atlantic rifted margin R.B. Trumbull; R.B. Trumbull GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany e-mail: bobby@gfz-potsdam.de Search for other works by this author on: GSW Google Scholar M. Sudo; M. Sudo Institute of Geosciences, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany e-mail: msudo@geo.uni-potsdam.de Search for other works by this author on: GSW Google Scholar C. Harris; C. Harris Department of Geological Sciences, University of Cape Town, Rondebosch, 7700 South Africa e-mail: chris.harris@uct.ac.za Search for other works by this author on: GSW Google Scholar R.A. Armstrong; R.A. Armstrong Research School of Earth Sciences, Australian National University, Canberra, Building 142, Mills Road, ACT 0200, Australia e-mail: richard.armstrong@anu.edu.au Search for other works by this author on: GSW Google Scholar C.H. de Beer C.H. de Beer Council for Geoscience, 3 Oos Street, Bellville, 7535 South Africa e-mail: cdebeer@geoscience.org.za Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2019) 122 (1): 69–78. https://doi.org/10.25131/sajg.122.0007 Article history first online: 03 Mar 2019 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R.B. Trumbull, M. Sudo, C. Harris, R.A. Armstrong, C.H. de Beer; The age of the Koegel Fontein anorogenic complex, South Africa, and its relationship to the regional timing of magmatism and breakup along the South Atlantic rifted margin. South African Journal of Geology 2019;; 122 (1): 69–78. doi: https://doi.org/10.25131/sajg.122.0007 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 SocietySouth African Journal of Geology Search Advanced Search Abstract The early Cretaceous Koegel Fontein intrusive complex is situated near the Atlantic coast in South Africa, about 350 km northwest of Cape Town. The complex comprises felsic units of granite and syenite with compositionally related dykes, and a single intrusive plug of diorite. Existing zircon U-Pb ages of 144 ± 2 Ma for the syenite and 133.9 ± 1.3 Ma for the granite suggest that the emplacement of the complex took place over a period of about 10 My. This study provides additional and independent ages of the Koegel Fontein complex by 40Ar/39Ar dating to confirm the onset and duration of magmatism and better define the sequence of igneous units that comprise it.New laser step-heating 40Ar/39Ar ages on plagioclase and biotite from the main intrusive units in the complex are presented here, including samples previously dated by U-Pb dating. The 40Ar/39Ar ages for the granite and syenite units (131.1 ± 0.9 Ma and 143.3 ± 0.9, respectively) are in good agreement with the zircon U-Pb ages. Other units not previously dated include the Rooivleitjie alkaline granite (150.7 ± 0.6 Ma), two quartz-porphyry dykes (143.0 ± 0.9 and 139.4 ± 1.7 Ma) and the Zout Rivier diorite plug (133.0 ± 1.0 Ma). The new results confirm an early onset of magmatism at Koegel Fontein relative to that of the Etendeka Province some 1000 km to the north, which is consistent with the regional south-to-north propagation of South Atlantic rifting. The youngest 40Ar/39Ar ages at Koegel Fontein (134 to 131 Ma, Rietpoort Granite and 133 Ma, Zout Rivier diorite) correspond to the age of the first magnetic seafloor-spreading anomaly offshore, and we suggest that the longevity of Koegel Fontein magmatism relates to a superposition of pre-drift magmatism onshore and spreading-related magmatism as continental separation began. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.Keywords:
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