Geochemistry and origin of late archean volcanic rocks from the rhenosterhoek formation,dominion group,South Africa |
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| Institution: | 1. Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA;2. Independent Researcher, Honolulu, HI 96815, USA;3. Department of Geological Sciences and Geological Engineering, Queen''s University, Kingston, ON K7L 3N6, Canada;4. Geochronology and Tracers Facility, British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;1. Centre for Earth Sciences, Indian Institute of Science, Bangalore 560012, India;2. Department of Geology, Niigata University, Niigata 950-2181, Japan;3. Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia;1. Centre for Exploration Targeting — Curtin node, Department of Applied Geology, Western Australian School of Mines, Curtin University, WA 6102, Australia;2. Geological Survey of Western Australia, Mineral House, 100 Plain Street, East Perth, WA 6004, Australia;3. Department of Applied Geology, Western Australian School of Mines, Curtin University, WA 6102, Australia;4. GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia |
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| Abstract: | The Rhenosterhoek Formation, composed chiefly of subaerial volcanic rocks, is part of the Dominion Group (∼ 2.8 Ga) which rests unconformably on older continental crust in South Africa. Chemical compositions of volcanic rocks from three drillcores of this formation do not show systematic differences either between or within cores. Major and immobile trace-element contents indicate that the volcanics are basaltic andesites and andesites with calc-alkaline affinities. Incompatible trace-element distributions are similar to those of modern andesites from evolved island arcs or continental-margin arcs.Geochemical modeling indicates that the basaltic andesites and andesites can be produced by open-system fractional crystallization with olivine, clinopyroxene and plagioclase as principal liquidus phases. Up to 10% contamination with continental crust is also allowed by the data. This succession does not appear to have formed in an oceanic or in a continental-margin arc, but may have formed adjacent to a continental-margin arc system in an incipient foreland basin on the Kaapvaal Craton. |
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