SHRIMP dating of zircons in eclogite from the Variscan basement in north-eastern Sardinia (Italy)

Abstract

SHRIMP (Sensitive High-Resolution Ion Microprobe) U-Pb ages of zircons from a single sample of mafic eclogite (Punta de li Tulchi, Sardinia, Italy) are reported. The study under cathodoluminescence (CL) reveals two groups of metamorphic zircons and the SHRIMP analyses allow recognition of three ages: 1) 453 ± 14 Ma; 2) 400 ± 10 Ma, and 3) 327 ± 7 Ma. The age of 453 ± 14 Ma could be that of the magmatic protolith and an age of 327 ± 7 Ma can reasonably be attributed to the main Variscan collisional event in Sardinia, which produced Barrovian-type metamorphism, and retrogression of eclogite under amphibolite-facies metamorphism. The intermediate age 400 ± 10 Ma is difficult to interpret and it could represent either the age of the eclogite facies metamorphism or it is a result of Pb-loss during the main Variscan event at 327 ± 7 Ma.