Journal
INTERNATIONAL JOURNAL OF EARTH SCIENCES
Volume 104, Issue 5, Pages 1167-1183Publisher
SPRINGER
DOI: 10.1007/s00531-015-1149-3
Keywords
Igneous zircon; U-Th-Pb SHRIMP data; Crustal- and mantle-derived magmas; Intra-orogenic extension; Early Carboniferous; Ossa-Morena Zone
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Funding
- [GOLD-PTDC/GEO-GEO/2446/2012]
- [FCOMP-01-0124-FEDER-029192]
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CL imaging and U-Th-Pb data for a population of zircons from two of the A parts per thousand vora 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 A degrees 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.
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