All lithologies are lenticular in shape and elongate parallel to the dominant S2 foliation, as shown in Fig. 1.
Six stages of structural evolution have been separated on the base of overprinting relationships: pre-D1 igneous structures; D1, D2 and D3 ductile deformation phases of Alpine age and fracture systems filled by peculiar mineral assemblages, ascribed to post-D2 and post-D3 stages.
Pre-D1 planar structures (magmatic layering ) are tens of centimetres-thick layers of amphibole-bearing eclogites alternate to tens of centimetres -thick layers of Hbl-Grt or Hbl-Grt-Zo/Czo metabasics (Figs. 2a and b). These planar structures are preserved only in metric relict domains.
D1 consists of a S1 foliation; it is a mm to cm-spaced foliation, preserved only in metre-size eclogites (Fig. 2) and Amp-schists; S1 is defined by the Shape Preferred Orientation (SPO) of Amp, Ep and Wm.
D2 structures are represented by the S2 foliation, a mm to cm-size differentiated layering. S2 is marked by SPO of Amp, Ep, ± Omp, ± Wm and ± Chl in eclogites, metabasics and schists; it is a differentiated layering of Srp ± Amp in serpentinites and ultramafics. D2 rootless folds are centimetre to m-size relics, better preserved in Amp-schists and eclogites (Figs. 1 and 2). S2 is the most penetrative planar structure at the scale of the Ivozio complex. In eclogites Omp grains, up to cm in size, define a mineral lineation (L2) within S2. In syn-D2 low strain volumes of eclogites, randomly oriented cm-size Omp-Lws and Grt grains overgrow the S1 foliation marked by a SPO of Amp. An internal foliation, marked by Amp ± Wm, is preserved within Omp and Grt porphyroblasts (Fig. 2). Locally D3 open folds, refold S1 and S2 foliations and lithological boundaries (Figs. 1, 2).
Four types of veins were distinguished on the basis of their mineral composition (Fig. 1 Schmidt diagrams): Omp, Gln, Ep and Grt veins. Overprinting relationships between veins and above described foliations/folds allowed to infer a relative timing:
Grt-bearing veins are generally massive and up to 1 m-length; two orientations exist, generally forming an angle of about 30°. In place Grt-veins display an Omp-rich rim.
Omp-bearing veins are scarce. They cut across the S1 foliation marked by Amp ± Wm (Fig. 2); close to the Omp fractures (up to 20 cm) Amp underlying the S1 foliation are replaced by randomly oriented Omp. Omp may be rimmed by aggregates of Gln.
Gln-bearing veins display three principal orientations at about 30° (Fig. 1). They cross cut both S1 and S2 foliations. In place Gln may also be rimmed by Omp. These observations lead to the interpretation that at least one generation of Gln veins predate the Omp-bearing veins development.
Ep-bearing veins are characterized by fibrous growth of Ep grains perpendicular to the vein wall. Ep veins may be up to 3 cm in thickness. Locally Ep is intergrown with Gln and may also display rims of Gln and/or Omp.
In places veins filled by Grt, Omp and Gln are reoriented during D3 folding.