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Geochemistry, Geochronology and Isotopic Evolution of the Chewore-Rufunsa Terrane, Southern Irumide Belt: a Mesoproterozoic Continental Margin Arc |
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| Authors: | Johnson Simon P; de Waele Bert; Tembo Francis; Katongo Crispin; Tani Kenichiro; Chang Qing; Iizuka Tsuyoshi; Dunkley Daniel |
| Institution: | 1Institute for Research on Earth Evolution, Japan Agency for Marine–Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka, Kanagawa-Ken, 237-0061, Japan 2Tectonics Special Research Centre, School of Earth and Geographical Sciences, University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia 3School of Mines, Geology Department, University of Zambia, Po Box 32379, Lusaka, Zambia 4Laboratory for Planetary Sciences, Tokyo Institute of Technology, 2-1-12 O-Okayama, Meguro, Tokyo, 152-8551, Japan 5National Institute of Polar Research, 9-10 Kaga 1-Chome, Itabashi-Ku, Tokyo 173-8515, Japan |
| Abstract: | The southern Irumide Belt (SIB) is an ENE–WSW-trending,late Mesoproterozoic orogenic belt located between the Congo–Tanzania–Bangweulu(CTB) and Kalahari cratons in central southern Africa. It isseparated from the late Mesoproterozoic Irumide Belt (IB) tothe north by Permo-Triassic graben, raising the possibilitythat the younger rifts reactivated a suture between the twobelts that has been rendered cryptic as a result of youngerKaroo cover. Both belts are dominated by calc-alkaline gneisses,but in addition the SIB contains abundant metavolcanic and metasedimentaryrocks. In this study we present detailed geochemical, isotopicand geochronological data for volcanic and plutonic lithologiesfrom the southernmost part of the SIB, the Chewore–RufunsaTerrane. This terrane comprises a wide variety of supracrustalto mid-crustal rocks that have major- and trace-element compositionssimilar to magmas formed in present-day subduction zones. Chondrite-normalizedrare earth element (REE) profiles and whole-rock Sm–Ndisotope compositions indicate that the parental supra-subductionmelts interacted with, and were contaminated by sialic continentalcrust, implying a continental-margin-arc setting. Secondaryionization mass spectrometry dating of magmatic zircon has yieldedcrystallization ages between c. 1095 and 1040 Ma, similar toelsewhere in the SIB. U–Pb dating and in situ Lu–Hfisotopic analyses of abundant xenocrystic zircon extracted fromthe late Mesoproterozoic granitoids indicate that the contaminantcontinental basement was principally Palaeoproterozoic in ageand had a juvenile isotopic signature at the time of its formation.These data are in contrast to those for the IB, which is characterizedby younger, c. 1020 Ma, calc-alkaline gneisses that formed bythe direct recycling of Archaean crust without significant additionof any juvenile material. We suggest that the SIB developedby the subduction of oceanic crust under the margin of an unnamedcontinental mass until ocean closure at c. 1040 Ma. Subsequentcollision between the SIB and the CTB margin led to the cessationof magmatism in the SIB and the initiation of compression andcrustal melting in the IB. KEY WORDS: geochemistry; Mesoproterozoic; SHRIMP zircon U–Pb dating; Sm–Nd isotopes; Southern Irumide Belt |
| Keywords: | : geochemistry Mesoproterozoic SHRIMP zircon U– Pb dating Sm– Nd isotopes Southern Irumide Belt |
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