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Istituto di Geoscienze e Georisorse     
Giacomini F., Braga R., Tiepolo M., Tribuzio R. New constraints on the origin and age of Variscan eclogitic rocks (Ligurian Alps, Italy). In: Contributions To Mineralogy and Petrology, vol. 153 (1) pp. 29 - 53. Springer, 2007.
 
 
Abstract
(English)
Gabbro and eclogite boudins are preserved within the amphibolites of the composite para- and ortho-gneiss Variscan basement of the Savona Crystalline Massif (Ligurian Brianšonnais, 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.
URL: http://www.springerlink.com/openurl.asp?genre=journal&issn=0010-7999
Subject Variscan
eclogite
Gabro
zircon
geochronology
LA-IPC-MS
Ligurian Alps
Italy


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