Italian Journal of Geosciences - Vol. 143 (2024) f.2

In situ garnet U-Pb dating of granulitized eclogites from NE Sardinia, Italy

Gabriele Cruciani1, Lorenzo Dulcetta1, Marcello Franceschelli1, Aratz Beranoaguirre2,3, Leo J. Millonig3 & Axel Gerdes3
1Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari – S.S. 554 Cittadella Universitaria, 09042, Monserrato (CA), Italy.
2Institut für Angewandte Geowissenschaften, Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany.
3Frankfurt Isotope and Element Research Center (FIERCE), Goethe-University Frankfurt, Frankfurt, Germany.
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Volume: 143 (2024) f.2
Pages: 226-236


A sample from the Punta de li Tulchi granulitized eclogite, cropping out within the Variscan migmatites of NE Sardinia, was investigated by LA-ICPMS garnet U–Pb dating. The majority of U-Pb analyses define a regression line with a lower intercept date of 395.1 ± 9.8 / 12.4 Ma. In addition, nine data points define a second regression line with a lower intercept date of 355.0 ± 18.1 / 19.4 Ma. The ~395 Ma age is interpreted to represent initial garnet growth during eclogite facies metamorphism. This age is another indication for an extensive subduction event at 380-400 Ma during the Variscan orogeny, as reported from other areas of the European Variscides. The ~355 Ma age is interpreted to indicate partial Pb-loss or fluid-mediated recrystallization of the garnet during the amphibolite to granulite facies metamorphism. This work demonstrates that in situ garnet U-Pb dating by LA- ICPMS is a powerful tool for deciphering the evolution of metamorphic rocks and that this method can provide valuable information and context for the interpretation of geochronological U-Pb data obtained from other geochronometers such as zircon.


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