The geology,petrology, geochronology and source region character of the layered gabbronoritic Oranjekom Complex in the Kibaran Namaqua mobile belt,South Africa |
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| Institution: | 1. Hugh Allsopp Laboratory, Bernard Price Building, University of the Witwatersrand, Wits 2050, South Africa;2. Department of Geology, University of the Orange Free State, Bloemfontein, South Africa;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Institute of Earth Science, Chinese Academy of Sciences, Beijing 100029, China;3. Faculty of Geology and Geophysics, Göttingen University, Göttingen 37077, Germany;1. Blue Water Marine Research, PO Box 402081, Tutukaka, 0153, New Zealand;2. National Institute of Water and Atmospheric Research, Private Bag 99940, Auckland, 1149, New Zealand;3. National Research Bureau, PO Box 10118, Auckland, 1446, New Zealand;1. Department of Geology, University of Maryland, 8000 Regents Dr, College Park, MD 20742, United States of America;2. Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, United States of America |
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| Abstract: | The Oranjekom Complex, a small mafic to anorthositic layered intrusion situated on the eastern margin of the Namaqua Mobile Belt, forms part of a number of such intrusions that were intruded early in the evolution of the belt. These have subsequently been deformed and isochemically metamorphosed to amphibole-bearing rocks. Petrographic and geochemical evidence indicates that the magmas were alumina-rich and that plagioclase was the primary liquidus phase, but in situ differentiation trends are shown mainly by the mafic phases. This implies that plagioclase crystals, although present in the magma, remained partially in suspension, whereas the mafic minerals accumulated. This is supported by both major and trace element character of the rocks. The RbSr and SmNd isotopic systems indicate that the Oranjekom Complex was intruded and metamorphosed at ca. 1100 Ma. This was followed by further metamorphism at ca. 944 Ma. The isotopic character indicates a depleted mantle source, that gives an age slightly older but within error of the estimated time of intrusion. Further data is required to precisely constrain the age of intrusion of these important markers in the evolution of the Namaqua Orogen. The isotope data indicate that there was limited crustal interaction indicating a thin (possibly juvenile) crust at that time. |
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