Metamorphic veins from the serpentinites of the Piemonte Zone, western Alps, Italy: a review.

The petrographic and micro-Raman analysis of the metamorphic veins occurring in serpentinites from the Piemonte Zone (Western Alps) has allowed to recognise seven different vein generations, developed at different P-T-X conditions. The first vein generation (balangeroite + magnetite + FeNi-alloys) formed during the Alpine prograde evolution, whereas the second vein generation (diopside + Ti-clinohumite + olivine + antigorite + Mg-chlorite) is related to the high pressure (eclogite-facies) metamorphic peak. All the others vein generations developed during the retrograde evolution, at different P-T conditions, moderate for types 3 (carlosturanite + antigorite + diopside + garnet) and 4 (antigorite + diopside) and low or very low for types 5 (chrysotile), 6 (tremolite + calcite) and 7 (brucite + magnetite and talc + calcite). The detail petrographic analysis of the metamorphic veins occurring in serpentinites gives complementary information to the conventional thermobarometric estimates based on the associated basic rocks and consequently is a powerful method to reconstruct the P-T path of the ophiolitic units.