The relations between metamorphism and deformation show very similar characteristics all over the studied transects although detailed studies on metamorphism and P-T-t paths are available only for the NW (Carmignani et al., 1979; Franceschelli et al., 1990; Ricci, 1992; Simpson, 1999; Carosi & Oggiano, 2002; Carosi et al., 2004) and the NE areas (Franceschelli et al., 1982; 1989; Ricci, 1992; Carosi & Palmeri, 2002; Di Vincenzo et al., 2004; Ricci et al., 2004). In the Anglona and Gallura areas, relatively small amount of data are available (Oggiano & Di Pisa, 1992; Ricci, 1992). Where S2 is the most prominent fabric in the sheared rocks, the S1 foliation consists of aligned inclusion trails within grt, pl, st and ky Barrovian porphyroblasts, which define a foliation made of quartz, flakes of phengite, biotite, chlorite, albite, almandine garnets and ilmenite. Syn-D1 garnet within albite porphyroblasts shows an increase of MgO from core to rim and a CaO content lower with respect to the core of garnets that grow along S2 foliation in the same thin section (Franceschelli et al., 1982; Carosi & Palmeri, 2002). The latter suggests a growth zoning and an increase of pressure from the growth of syn-D1 garnet to syn-D2 garnet of the albite-garnet zone. The growth of the Barrovian index minerals was post-D1 deformation phase and partly during the early stages of the D2 deformation phase (Franceschelli et al., 1982, 1989; Carosi & Palmeri, 2002; Di Vincenzo et al., 2004; Ricci et al., 2004). Occasionally, plagioclase porhyroblasts have the S1 foliation truncated by the external S2 foliation. In other cases, plagioclase shows a sigmoidal internal foliation continuing to the S2 foliation, suggesting a syn-D2 growth of plagioclases during the D2 deformation. The S2 foliation is defined by white mica, biotite, chlorite, quartz, small size albite and/or oligoclase and garnet. White mica has a phengitic composition in the core of the large flakes of the garnet zone and is a muscovite near the rim or along the S2 foliation of the higher grade zones.
Millimeter-size garnet porphyroblasts (3-4 mm) in the garnet and staurolite zones are idioblastic almandines and show snow-ball inclusion trails related to their rotation during D2. Occasionally they show an increasing grain size of quartz inclusions from core to rim, suggesting a temperature increase during their growth. This is chemically evidenced by the increase of XMg and the decrease of XMn from core to rim which is indicative of a prograde zoning (Tracy, 1983; Franceschelli et al., 1982; Carosi & Palmeri, 2002). The decrease of the XCa content from core to rim for the same syn-D2 garnet is indicative of a growth during decompression (Crawford, 1977; Carswell, 2000; Carosi & Palmeri, 2002; Ricci et al., 2004). Small size almandines are homogeneous but a decrease of MgO and an increase of MnO detected at the extreme edges indicate a reverse zoning (Grant and Veiblen, 1971). The sense of rotation of asymmetric inclusion trails on plagioclases and rotated garnets is the same as deduced from shear band cleavages and mica fish. Staurolite and kyanite porphyroblasts show evidence of pre- and, rarely, syn-D2 growth (Fig. 6b). They contain inclusions of rounded idioblastic prograde almandines, biotite and ilmenite.
Some grt, st and ky porphyroblasts are fractured, stretched and show asymmetric strain fringes, made of quartz, biotite and chlorite. The S2 schistosty in the staurolite and kyanite zones is marked by quartz, oligoclase, muscovite, biotite, and almandines (Fig. 6b) showing an increase of MnO and a decrease of MgO at the rim indicative of the reverse zoning. Chlorite is also present but is interpreted to be as a secondary phase.
Relations between metamorphism and deformation show that the Barrovian index minerals (bt, grt, st and ky) grew often as porhyroblasts pre- or during the early stages of D2 deformation. Matrix minerals are aligned along the S2 foliation and involved a diachronous development of the main metamorphic equilibria in the different metamorphic zones (Franceschelli et al, 1989; Ricci et al., 2004).
The relations between deformation and metamorphism and petrological data in the Nurra transect provide similar results as in the Baronie area (Carmignani et al., 1979; Franceschelli et al., 1990). The metamorphic peak was attained post-D1 and pre- up to syn D2. Syn-D1 phengitic white micas indicate higher pressures (nearly 7-8 Kbar) with respect to the D2 deformation phase
On the other hand the P-T-t evolution reported in Franceschelli et al. (1989), Carosi & Palmeri (2002), Di Vincenzo et al., (2004) and Ricci et al., (2004 with references therein), clearly shows that D2 deformation developed after metamorphic peak (pre to syn-D2) in a regime of decreasing pressure all over the Barrovian metamorphic zones.