%0 Journal Article
%A Villaseca González, Carlos
%A Orejana García, David
%A Belousova, Elena
%A Armstrong, Richard A.
%A Pérez-Soba Aguilar, Cecilia María
%A Jeffries, Teresa E.
%T U–Pb isotopic ages and Hf isotope composition of zirconsin Variscan gabbros from central Spain: evidence of variablecrustal contamination
%D 2011
%@ 0930-0708
%U https://hdl.handle.net/20.500.14352/42408
%X Ion microprobe U–Pb analyses of zircons fromthree gabbroic intrusions from the Spanish Central System(SCS) (Talavera, La Solanilla and Navahermosa) yieldVariscan ages (300 to 305 Ma) in agreement with recentstudies. Only two zircon crystals from La Solanilla massifgave slightly discordant Paleoproterozoic ages (1,848 and2,010 Ma). Hf isotope data show a relatively large variationwith the juvenile end-members showing ɛHfi values as highas +3.6 to +6.9 and +1.5 to +2.9 in the Navahermosa andTalavera gabbros, respectively. These positive ɛHfi values upto +6.9 might represent the composition of the subcontinentalmantle which generates these SCS gabbros. This ɛHfirange is clearly below depleted mantle values suggesting theinvolvement of enriched mantle components on the origin ofthese Variscan gabbros, and is consistent with previouswhole-rock studies. The presence of zircons with negativeɛHfi values suggest variable, but significant, crustal contaminationof the gabbros, mainly by mixing with coeval granitemagmas. Inherited Paleoproterozoic zircons of La Solanillagabbros have similar trace element composition (e.g. Th/Uratios), but more evolved Hf-isotope signatures than associatedVariscan zircons. Similar inherited ages have beenrecorded in zircons from coeval Variscan granitoids from theCentral Iberian Zone. Granitic rocks have Nd model ages(TDM) 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 Proterozoiczircons in La Solanilla gabbro indicate the presence ofreworked Archean protoliths (TDM2 model ages of 3.0 to3.2 Ga) incorporated into the hybridized mafic magma.
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