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Variscan metamorphism in Sardinia, Italy: review and discussion
Abstract:
The Sardinian segment of the Variscan chain is divided into four tectono-metamorphic zones from NE to SW: 1) Inner zone, with medium- to high-grade metamorphic rocks and migmatites; 2) Internal Nappe zone, with low- to medium-grade rocks; 3) External Nappe zone, with low-grade metamorphic rocks; 4) External zone, with very low- to low-grade rocks. Metabasite lenses, with eclogite and granulite relics, occur in the migmatites.
Pre-Variscan ages are attributed to the E-W trending folds below the Sardic unconformity (SW Sardinia). Five Variscan deformation phases have been distinguished, the principal ones being: D
For Inner zone sequences, a complete prograde sequence has been recognised, from the chlorite zone to the sillimanite + K-feldspar one. The Nappe zone shows decreasing metamorphic grade from bottom to top of the Nappe pile, as well as in each single unit. The Variscan P-T-t path is the clockwise loop typical of continental collision. For the Barrovian stage, thermobarometers yielded a P
The Corsica-Sardinia microplate belongs to the southern passive margin of the Hun Superterrane of the Swiss authors. The beginning of Variscan continental collision is marked by a probable eclogite-producing HP event. Ages of 355-335 Ma and 335-320 Ma for the first two Variscan metamorphic phases and 310-280 Ma and 290-280Ma for late-post orogenic Variscan magmatism in Sardinia match those of the same events in the northern Hun Superterrane active leading margin.
The Variscan Corsica-Sardinia batholith is made up of late-orogenic calc-alkaline intrusive rocks and post orogenic leucogranites. The greater volumes (surface area≈ 12000 Km
DOI:
10.3809/jvirtex.2005.00121