Petrogenesis of a late-Variscan rhyodacite at the Ossa Morena-Central Iberian zones boundary,Iberian Massif,Central Portugal: Evidence for the involvement of lithospheric mantle and meta-igneous lower crust |
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| Institution: | 1. Geobiotec, LNEG: Geology, Hydrogeology and Coastal Geology Department, Estrada da Portela, Bairro do Zambujal, Ap. 7586-Alfragide, 2610-999 Amadora, Portugal;2. Geobiotec, Department of Earth Sciences, University of Coimbra, 3030-790 Coimbra, Portugal;3. Earth Sciences Department, Memorial University, St. John’s, NL A1B 3X5, Canada;1. Institutes of Geosciences, Friedrich-Schiller University, Burgweg 11, D-07749 Jena, Germany;2. Department of Material Research and Physics, Division Mineralogy, University of Salzburg, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria;3. Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen Ø, Denmark;4. Karlsruhe Institute of Technology, ANKA Synchrotron Radiation Facility, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany;1. School of Lisiguang, China University of Geosciences (Wuhan), Wuhan 430074, PR China;2. State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, East Beijing Road 39, Nanjing 210008, PR China;3. Key Laboratory of Economic Stratigraphy and Palaeogeography of the Chinese Academy of Sciences, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, PR China;4. University of Chinese Academy of Sciences, Beijing 100049, PR China;5. Central Asia Oil & Gas Institute of Research Institute of Exploration and Development, Xinjiang Oilfield Company, Karamay 834000, Xinjiang Uygur Autonomous Region, PR China;6. Social and Economic Development Research Center of Karamay, Karamay 834000, Xinjiang Uygur Autonomous Region, PR China;1. Gmain Nr. 1, 84424 Isen, Germany;2. Hydroisotop GmbH, Woelkestrasse 9, 85301 Schweitenkirchen, Germany,;3. UMR GeoRessources 7359, Université de Lorraine. 54506 Vandoeuvre-lès-Nancy Cedex, France;4. Norges Geologiske Undersøkelse, 7491 Trondheim, Norway;5. Natural History Museum, Cromwell Road, London SW7 5 BD, United Kingdom;6. Institut für Mineralogie, TU Bergakademie Freiberg, Brennhausgasse 14, 09596 Freiberg, Germany;7. Secretaria de Mineria, Av. Hipólito Yrigoyen 401, 5000 Córdoba, Argentina;1. St. Kl. Ohridski University of Sofia, 15, Tsar Osvoboditel Blvd., 1504 Sofia, Bulgaria;2. Institute of Organic Chemistry, Bulgarian Academy of Sciences, 9 Bldg., Acad. G. Bonchev Str., 1113 Sofia, Bulgaria;3. Geological Institute, Bulgarian Academy of Sciences, 24 Bldg., Acad. Bonchev Str., 1113 Sofia, Bulgaria;1. Department of Physics, Foshan University, Foshan 52800, China;2. Horia Hulubei National Institute for Physics and Nuclear Engineering, P.O.B. MG-6, RO-077125 Magurele-Bucharest, Romania;3. School of Electronics and Information, Guangdong Polytechnic Normal University, Guangzhou 510665, China |
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| Abstract: | A late-Variscan rhyodacite is exposed at the contact between the Ossa Morena Zone and the Central Iberian Zone of the Iberian Massif, Central Portugal. Dykes of rhyodacite intruded the Série Negra Unit and the Sardoal Complex that are part of the Cadomian basement. The igneous crystallization age of the rhyodacite (308 ± 1 Ma) was obtained on igneous monazite by the ID-TIMS U-Pb method. It is broadly coeval with the emplacement of late-Variscan granitoids during the last deformation phase of the Variscan Orogeny (ca. 304–314 Ma) and with the development of the large late-Variscan strike-slip shear zones (ca. 307 Ma). The rhyodacite samples are calc-alkaline, show identical composition and belong to the same magmatic sequence. The rhyodacite isotopic signatures (Sm-Nd and δ18O) are consistent with depleted-mantle juvenile sources and the contribution of the meta-igneous lower crust. The input of mantle juvenile sources is related to Variscan reactivation of lithospheric fractures. The inherited Neoproterozoic (ca. 619 Ma) and Mesoproterozoic (ca. 1054 Ma) zircon ages, are similar to those of the Central Iberian Zone. This suggests that lower crust of the Central Iberian Zone was involved in the magma generation of the rhyodacite. Coeval late-Variscan magmatic rocks display a larger contribution from ancient crustal components, which may be attributed to the smaller volume and faster cooling rate of the rhyodacite and consequent lower melting of the crust. Mixing of juvenile mantle-derived melts with melts from the lower continental crust was followed by fractional crystallization of garnet and amphibole that remained in the source. Fractional crystallization of plagioclase, biotite, quartz and zircon occurred in shallower magma chambers. Fractional crystallization of zircon was not significant. |
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| Keywords: | Carboniferous Igneous monazite Inherited zircon ID-TIMS U-Pb geochronology |
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