U-Pb zircon and Ar-Ar amphibole ages from Sardinian migmatites (Italy) and review of migmatite ages from the Variscan belt

Abstract

U-Pb zircon age determinations and Ar-Ar dating on biotite and amphibole were performed on amphibole-bearing migmatite samples. The mesosome zircons yield a weighted average age of 461.3 ± 3.3 Ma (U-Pb concordant data). Leucosome, yielded U-Pb zircon ages clustering around 460 Ma (weighted average age of 462.5 ± 2.4 Ma, U-Pb concordant data) in core and oscillatory zoning domains. Zircon rims yielded an average value of 324.2 ± 4.0 Ma. The Ar-Ar amphibole age of 317.4 ± 2 Ma is interpreted as the age of chemical re-equilibration and cooling of this mineral. An Ar-Ar age determination on biotite yielded a total gas age of 283 Ma interpreted as a minimum argon age owing to Ar loss due to interlayered chlorite. The migmatite age of 324.2 ± 4.0 Ma fall in the 335-320 Ma interval that concentrates 76% of migmatite ages from the Variscan Belt.