Crystallization and age of zircon from Corsican ophiolitic albitites: consequences for oceanic expansion in Jurassic times

In Corsica, albitites and albite-granites are considered to be the latest products of an ophiolitic magma. Two albitites have been selected for a study of the morphology, typology and age of their zircons, applying for the first time the U-Pb method to Western Tethyan ophiolites. Both samples come from the Rospigliani series, possibly formed in a transform fault zone. The first one shows a cumulate texture, whereas the second has features indicative of more rapid cooling. Zircons have precipitated at the end of the fractional crystallization process after a strong enrichment in alkali and incompatible elements. In a typological diagram they plot at high temperature and high agpaicity indexes. These abundant large, euhedral to subhedral zircons, sometimes with fine zoning, may also contain inclusions of granitic composition which testifies to K fractionation in ophiolitic magmas. The U-Pb age of 161±3Myr is in the range of the ages obtained for Alpine and Apennines ophiolites. All these ophiolitic remnants belonging to the Liguro-Piedmont Basin may represent a portion of the Central Atlantic Ocean created during Middle and Upper Jurassic times.