International Journal of Earth Sciences

, Volume 104, Issue 5, pp 1167–1183

The multistage crystallization of zircon in calc-alkaline granitoids: U–Pb age constraints on the timing of Variscan tectonic activity in SW Iberia

  • M. F. Pereira
  • M. Chichorro
  • P. Moita
  • J. F. Santos
  • A. M. R. Solá
  • I. S. Williams
  • J. B. Silva
  • R. A. Armstrong
Original Paper

DOI: 10.1007/s00531-015-1149-3

Cite this article as:
Pereira, M.F., Chichorro, M., Moita, P. et al. Int J Earth Sci (Geol Rundsch) (2015) 104: 1167. doi:10.1007/s00531-015-1149-3

Abstract

CL imaging and U–Th–Pb data for a population of zircons from two of the Évora Massif granitoids (Ossa-Morena Zone, SW Iberia) show that both calc-alkaline granitoids have zircon populations dominated by grains with cores and rims either showing or not showing differences in Th/U ratio, and having ages in the range ca. 350–335 Ma (Early Carboniferous). Multistage crystallization of zircon is revealed in two main growth stages (ca. 344–342 Ma and ca. 336–335 Ma), well represented by morphologically complex zircons with cores and rims with different ages and different Th/U ratios that can be explained by: (1) crystallization from melts with different compositions (felsic peraluminous to felsic-intermediate metaluminous; 0.001 < Th/U ratio < 0.5) and (2) transient temperature fluctuations in a system where anatectic felsic melts periodically underwent injection of more mafic magmas at higher temperatures. The two studied calc-alkaline granitoids do not include inherited zircons (pre-Carboniferous), probably because they were formed at the highest grade of metamorphism (T > 837 °C; granulite facies) and/or because they were derived from inheritance-poor felsic and mafic rocks from a previous cycle, as suggested by the internal structures of zircon cores. These Variscan magmatic rocks with crystallization ages estimated at ca. 336–335 Ma are spatially and temporally related to high-temperature metamorphism, anatexis, processes of interaction between crustal- and mantle-derived magmas and intra-orogenic extension that acted in SW Iberia during the Early Carboniferous.

Keywords

Igneous zircon U–Th–Pb SHRIMP data Crustal- and mantle-derived magmas Intra-orogenic extension Early Carboniferous Ossa-Morena Zone 

Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  • M. F. Pereira
    • 1
  • M. Chichorro
    • 2
  • P. Moita
    • 3
  • J. F. Santos
    • 4
  • A. M. R. Solá
    • 5
  • I. S. Williams
    • 6
  • J. B. Silva
    • 7
  • R. A. Armstrong
    • 6
  1. 1.IDL/Departamento de Geociências, ECTUniversidade de ÉvoraÉvoraPortugal
  2. 2.CiCEGE/Departamento de Ciências da TerraUniversidade Nova de LisboaLisbonPortugal
  3. 3.Centro de Geofísica de Évora/Departamento de Geociências, ECTUniversidade de ÉvoraÉvoraPortugal
  4. 4.Geobiotec, Departamento de Geociências daUniversidade de AveiroAveiroPortugal
  5. 5.LNEG, Unidade de Geologia e Cartografia GeológicaPortoPortugal
  6. 6.Research School of Earth SciencesThe Australian National UniversityActonAustralia
  7. 7.IDL/Departamento de Geologia, Faculdade de CiênciasUniversidade de LisboaLisbonPortugal

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