U-Pb isotopic ages and Hf isotope composition of zircons in Variscan gabbros from central Spain: evidence of variable crustal contamination

Carlos Villaseca*, David Orejana, Elena Belousova, Richard A. Armstrong, Cecilia Pérez-Soba, Teresa E. Jeffries

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

Ion microprobe U-Pb analyses of zircons from three gabbroic intrusions from the Spanish Central System (SCS) (Talavera, La Solanilla and Navahermosa) yield Variscan ages (300 to 305 Ma) in agreement with recent studies. Only two zircon crystals from La Solanilla massif gave slightly discordant Paleoproterozoic ages (1,848 and 2,010 Ma). Hf isotope data show a relatively large variation with the juvenile end-members showing e{open}Hf i values as high as +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa and Talavera gabbros, respectively. These positive e{open}Hf i values up to +6.9 might represent the composition of the subcontinental mantle which generates these SCS gabbros. This e{open}Hf i range is clearly below depleted mantle values suggesting the involvement of enriched mantle components on the origin of these Variscan gabbros, and is consistent with previous whole-rock studies. The presence of zircons with negative e{open}Hf i values suggest variable, but significant, crustal contamination of the gabbros, mainly by mixing with coeval granite magmas. Inherited Paleoproterozoic zircons of La Solanilla gabbros have similar trace element composition (e.g. Th/U ratios), but more evolved Hf-isotope signatures than associated Variscan zircons. Similar inherited ages have been recorded in zircons from coeval Variscan granitoids from the Central Iberian Zone. Granitic rocks have Nd model ages (T DM) predominantly in the range of 1.4 to 1.6 Ga, suggesting a juvenile addition during the Proterozoic. However, Hf crustal model ages of xenocrystic Proterozoic zircons in La Solanilla gabbro indicate the presence of reworked Archean protoliths (T DM2 model ages of 3.0 to 3.2 Ga) incorporated into the hybridized mafic magma.

Original languageEnglish
Pages (from-to)151-167
Number of pages17
JournalMineralogy and Petrology
Volume101
Issue number3-4
DOIs
Publication statusPublished - Mar 2011

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