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The metamorphic evolution of a granulitized eclogite from Punta de li Tulchi NE Sardinia, Italy,\ud reconstructed utilizing a combined microstructural (symplectitic, coronitic and kelyphytic features) and\ud thermodynamic approach, involved a complex metamorphic history with equilibrium attained only at a\ud domainal scale. Microstructural analysis and mineral zoning allow recognition of reactants and products\ud involved in successive balanced mineral reactions. The P–T conditions at which each microstructure was\ud formed are further constrained by calculating isochemical phase diagrams (pseudosections) for the\ud composition of effectively reacting domains. A pre-symplectite stage developed during prograde\ud metamorphism under conditions ranging from 660-680°C, 1.6-1.8 GPa to 660-700°C at 1.7-2.1 GPa.\ud Pseudosections calculated for subsequent clinopyroxene + plagioclase and orthopyroxene +\ud plagioclase symplectitic coronae using the composition of effectively reacting microdomains temperature in excess of 800°C and pressures of 1.0-1.3 GPa. Modelling the development of later plagioclase + amphibole coronae around garnet during decompression yields conditions of 730-830°C and 0.8-1.1 GPa. H2O (wt%) isomodes indicate that the granulitized eclogites were H2O-undersaturated\ud at peak-P conditions and during most of the subsequent heating and decompression. This allowed the\ud preservation of prograde garnet zoning in spite of the strong granulite facies overprint. The P–T\ud evolution of Punta de li Tulchi granulitized eclogite is very similar in shape to that registered by other\ud NE Sardinia retrogressed eclogites thus suggesting a common tectonic scenario for their evolution

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 Ma, 457  2 Ma 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 Ma and 327 ± 7 Ma as the ages of the main Variscan retrograde events.\ud 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.\ud The following P-T ranges have been estimated for the different stages. Eclogite stage: 550°-700°C; 1.3-1.7 GPa; Granulite stage: 650°-900°C; 0.8-1.2 GPa, clustering in the range 1.0-1.2 GPa; Amphibolite stage: 550°-740°C; 0.3-0.7 GPa; Greenschist stage: 300°-400°C; 0.2-0.3 GPa. Comparable ranges characterise the other Variscan massifs in Europe: Eclogite stage: T=530°-800°C; P from 0.7-1.1 to 1.7 ± 0.3 GPa; Granulite stage : T=760°-870°C and P from 7.2-9.9 to 1.1-1.4 GPa, clustering around 1.0-1.2 GPa.\ud Whole-rock chemistry: Sardinian eclogites are N- to T-MORB; European ones N- to E-MORB or calc-alkaline.\u

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