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Istituto di Geoscienze e Georisorse     
Franceschelli M., Puxeddu M., Cruciani G., Utzeri D. Metabasites with eclogite facies relies from Variscides in Sardinia, Italy: a review. In: International Journal of Earth Sciences, vol. 96 (5) pp. 795 - 815. Springer, 2007.
 
 
Abstract
(English)
Metabasites with eclogite facies relics occur in northern Sardinia as massive to strongly foliated lenses or boudins embedded within low- to medium-grade rocks (Anglona) and migmatites (NE Sardinia). U-Pb zircon dating yielded 453 14, 457 2 and 460 5 Ma as the protolith ages; 400 10 and 403 4 Ma have been interpreted as the ages of the HP event and 352 3 and 327 7 Ma as the ages of the main Variscan retrograde events. A pre-eclogite stage is documented by the occurrence of tschermakite, zoisite relics within garnet porphyroblasts (Punta de li Tulchi) and an edenite-andesine inclusion within a relict kyanite porphyroblast (Golfo Aranci). Four main metamorphic stages have been distinguished in the eclogite evolution: (1) eclogite stage, revealed by the occurrence of armoured omphacite relics within garnet porphyroblasts. The Golfo Aranci eclogites also include kyanite, Mg-rich garnet and pargasite; (2) granulite stage, producing orthopyroxene and clinopyroxene-plagioclase symplectites replacing omphacite. At Golfo Aranci, the symplectitic rims around relict kyanite consist of sapphirine, anorthite, corundum and spinel; (3) amphibolite stage, leading to the formation of amphibole-plagioclase kelyphites between garnet porphyroblasts and pyroxene-plagioclase symplectites and to the growth of cummingtonite on orthopyroxene. Tschermakite to Mg-hornblende, plagioclase, cummingtonite, ilmenite, titanite and biotite are coexisting phases; (4) greenschist to sub-greenschist stage, defined by the appearance of actinolite, chlorite, epidote ss, titanite, sericite and prehnite. The following P-T ranges have been estimated for the different stages. Eclogite stage 550-700C; 1.3-1.7 GPa; granulite stage 650-900C; 0.8-1.2 GPa, clustering in the range 1.0-1.2 GPa; amphibolite stage 550-740C; 0.3-0.7 GPa; greenschist stage 300-400C; 0.2-0.3 GPa. Comparable ranges characterise the other Variscan massifs in Europe; eclogite stage: T = 530-800C; P from 0.7-1.1 to 1.7 0.3 GPa; granulite stage T = 760-870C and P from 1.1-1.4 to 7.2-9.9 GPa, clustering around 1.0-1.2 GPa. Whole-rock chemistry: Sardinian eclogites are N- to T-MORB; European ones N- to E-MORB or calc-alkaline.
URL: http://www.springer.com/earth+sciences+and+geography/geology/journal/531
Subject eclogite
retrograde metamorphic evolution
geochronology
Sardinia
correlations
geodynamic framework
Variscan orogeny


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