Gabbro and eclogite boudins are preserved within the amphibolites of the composite para- and ortho-gneiss Variscan basement of the Savona Crystalline Massif (Ligurian Briançonnais, Italy). Whole rock trace element patterns, low initial εNd (+5.4 to +8.8) data and trace element analyses on relict igneous clinopyroxene revealed that the mafic rocks were derived from depleted mantle melts, which most likely underwent crustal contamination during emplacement. Gabbros have a cumulus origin controlled by clinopyroxene and plagioclase segregation, whereas the eclogites represent evolved melts. U-Pb and trace element micro-analyses on zircons separated from one amphibolitised gabbro and one eclogite help to constrain coeval ages at -468 Ma for their igneous protoliths. The occurrence of a few inherited zircons confirms the involvement of a crustal component in the petrogenesis of the mafic rocks. In the eclogite, concordant zircon ages younger than the protolith age testify to metamorphic re-crystallisation (or new growth) from about 420 to 305 Ma. Zircon textures and trace element compositions indicate that eclogite facies metamorphism occurred 392-376 Ma ago. The younger zircon portions yielding a mean Concordia age of 333 ± 7 Ma are related to equilibration or new growth during the post-eclogite, amphibolite-facies equilibration.
New constraints on the origin and age of Variscan eclogitic rocks (Ligurian Alps, Italy) / F. Giacomini, R. Braga, M. Tiepolo, R. Tribuzio. - In: CONTRIBUTIONS TO MINERALOGY AND PETROLOGY. - ISSN 0010-7999. - 153:1(2007 Jan), pp. 29-53.
New constraints on the origin and age of Variscan eclogitic rocks (Ligurian Alps, Italy)
M. TiepoloPenultimo
;
2007
Abstract
Gabbro and eclogite boudins are preserved within the amphibolites of the composite para- and ortho-gneiss Variscan basement of the Savona Crystalline Massif (Ligurian Briançonnais, Italy). Whole rock trace element patterns, low initial εNd (+5.4 to +8.8) data and trace element analyses on relict igneous clinopyroxene revealed that the mafic rocks were derived from depleted mantle melts, which most likely underwent crustal contamination during emplacement. Gabbros have a cumulus origin controlled by clinopyroxene and plagioclase segregation, whereas the eclogites represent evolved melts. U-Pb and trace element micro-analyses on zircons separated from one amphibolitised gabbro and one eclogite help to constrain coeval ages at -468 Ma for their igneous protoliths. The occurrence of a few inherited zircons confirms the involvement of a crustal component in the petrogenesis of the mafic rocks. In the eclogite, concordant zircon ages younger than the protolith age testify to metamorphic re-crystallisation (or new growth) from about 420 to 305 Ma. Zircon textures and trace element compositions indicate that eclogite facies metamorphism occurred 392-376 Ma ago. The younger zircon portions yielding a mean Concordia age of 333 ± 7 Ma are related to equilibration or new growth during the post-eclogite, amphibolite-facies equilibration.Pubblicazioni consigliate
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