1170 Ma SHRIMP age for Koras Group bimodal volcanism, Northern Cape Province

J. Gutzmer, N.J. Beukes, A.L. Pickard, Mark Barley

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31 Citations (Scopus)

Abstract

The bimodal volcanic and coarse siliciclastic sedimentary rocks of the Koras Group are virtually undeformed and weakly metamorphosed, and overlie the highly metamorphosed and strongly deformed rocks of the Kheis subprovince of the Namaqua-Natal Metamorphic Province with a sharp erosional unconformity. Zircons from the Swartkopsleegte quartz porphyry, close to the base of the Koras Subgroup, have been dated at 1171 +/- 7 Ma by SHRIMP. This age is in good agreement with, but far more precise than, previously published ages for the Koras Group. The new age defines the onset of bimodal volcanism in the Koras Group and also indicates that the compressional Kibaran Orogeny in the Namaqua-Natal Province ended before or at similar to 1170 Ma. The main phase of Kibaran deformation. uplift, and erosion in the Namaqualand sector of the orogen took place in the period between the extrusion of the Wilgenhoutsdrif lavas at similar to 1330 Ma and deposition of the Koras Group at 1171 Ma. Younger ages for peak metamorphism and post-tectonic intrusions (1060 to 1030 Ma) in the Namaqua-Natal Province clearly post-date Kibaran compressional tectonics and magmatic activity by mon than 100 Ma and are related to a subsequent magmatic event in the orogen. The Koras Group in Namaqualand is widely regarded as a typical representative of the similar to 1105 Ma Umkondo igneous province, a group of volcano-sedimentary successions and igneous bodies which post-date the Kibaran Orogeny in southern Africa. However, extrusion of the Koras lavas predates the Umkondo suite in Zimbabwe and coeval lavas in Botswana and Namibia by 60 Ma.
Original languageEnglish
Pages (from-to)32-37
JournalSouth African Journal of Geology
Volume103
Issue number1
DOIs
Publication statusPublished - 2000

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