Pressure-temperature and deformational evolution of high-pressure metapelites from Variscan NE Sardinia, Italy

Chloritoid schists crop out north of the village of Lula in the Inner Zone of the Variscan chain of Sardinia consisting of a variety of metamorphic rocks. The S-1 and S-2 foliations in these schists are defined by the orientation of muscovite, paragonite, and chloritoid. Chlorite is an additional mineral oriented along S-2. Late margarite grew at the expense of chloritoid included in garnet Garnet porphyroblasts, enclosing quartz, chloritoid, rutile, Fe-oxide, apatite and paragonite, show a progressive decrease of spessartine component from 17 to 7 mol% and an increase of pyrope component from 4 to 6 mol% from core to rim. The grossular content firstly increases from the inner (Grs(similar to 21)) to the outer core (Grs(similar to 27)) and then decreases towards the outermost rim (Grs(similar to 15)). Compositional mapping of white mica also revealed zoning and a wide range in Si content (from 6.0 to 6.6 pfu). The highest Si content is related to the highest Fe and Mg contents and the lowest Na content P-T pseudosections were calculated in the system Na2O-K2O-CaO-FeO-MnO-MgO-Al2O3-TiO2-SiO2-H2O for compositions of chloritoid schists. The highest Si contents of K-white mica and the garnet core composition suggest pressures close to 1.8 GPa and temperatures of 460-500 degrees C. The garnet rim composition and low Si contents in K-white mica are compatible with re-equilibration at 540-570 C and 0.7-1.0 GPa. These results suggest an HP-metamorphic imprint during the D-1 deformation phase which occurred before the Baffovian amphibolite-facies metamorphism of NE Sardinia. D-2 folding and shearing occurred at decreasing P-T conditions during the exhumation of the metamorphic complex. (C) 2013 Elsevier B.V. All rights reserved.