P–T conditions for the eclogitic re‐equilibration of the metaophiolites from Val d'Ala di Lanzo (internal Piemontese zone, Western Alps)

Abstract A study has been made of the high‐pressure early‐Alpine re‐equilibration in the eclogites and metasedimentary cover of the Val d'Ala di Lanzo ophiolite. All of the main high‐pressure minerals have been analysed and their compositions used to determine re‐equilibration temperatures. The minimum conditions proposed ( P = 1.3 GPa, T = 450–460°C) are also indicated by the presence of a jadeite+quartz‐bearing metagranite. The temperatures are compared with those reported for similar eclogites from the Voltri Group, the Aosta Valley and the Valais. Comparison of recalculated temperatures shows that the temperature (and probably the pressure) of the eclogitic re‐equilibration increased in the Aosta Valley and the Valais, in keeping with what has been observed in the internal Penninic basement of the Gran Paradiso and Monte Rosa crystalline massifs.