Late Neoproterozoic,Ordovician and Carboniferous events recorded in monazites from southern-central Madagascar |
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| Institution: | 1. Development Research Center of Chinese Geological Survey, Beijing 100037, China;2. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;3. Beijing Institute of Geology for Mineral Resources, Beijing 100012, China;1. V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;2. Metally Altaya Joint-Stock Company, prosp. Kommunisticheskii 99, Gorno-Altaisk, Altai Republic, 649002, Russia pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia;3. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;4. A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, ul. Favorskogo 1a, Irkutsk, 664033, Russia;1. Hydrometallurgy Research Group, Department of Chemical Engineering, University of Cape Town, Private Bag X6, Rondebosch 7701, South Africa;2. Minerals to Metals Initiative, Department of Chemical Engineering, University of Cape Town, Private Bag X6, Rondebosch 7701, South Africa;3. School of Earth, Atmosphere and Environment, Building 28, 9 Rainforest Walk, Monash University, Clayton, VIC 3800, Australia;4. Centre for Minerals Research, Department of Chemical Engineering, University of Cape Town, Private Bag X6, Rondebosch 7701, South Africa;5. Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3168, Australia;6. Catalysis Institute, Department of Chemical Engineering, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa;1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. Department of Geosciences and Resources, China University of Geosciences, Beijing 100083, China;3. University of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | The evolution of the basement of southern Madagascar north and south of the Ranotsara shear zone was investigated using (U + Th)/Pb electron probe monazite age dating in combination with petrographic constraints. Several monazite grains show a stepwise progression of younger ages towards the rim indicating partial and complete resetting during tectonic, metamorphic and/or fluid events. The oldest ages, ranging from 630–2400 Ma, occur relatively rare in relic cores. A first, clear age-population is dated at 550–560 Ma. Most ages fall in two populations at 420–460 and 490–500 Ma, which in some samples overlap in error. We interprete these ages as dating low-pressure and high-temperature metamorphism. We have also clear evidence for Carboniferous (300–310 Ma) monazite overgrowth rims, which can not directly be related to macroscopic structures or metamorphic parageneses. In combination with literature data, we propose that the observed monazite age populations are related to Gondwana amalgamation and subsequent rifting events during the break up of Gondwana. Our study confirms that only the electron or ion microprobe yields sufficient spatial resolution to date individual shells of multiple zoned monazites in the polymetamorphic basement of Madagascar. |
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