A study of high-pressure metapelites from the Western Alps reveals a wide range of metamorphic grades, ranging from a Fe-Mg-carpholite zone, through an intermediate zone of magnesian chloritoid-talc-phengite, to a zone where coesite, pyrope, and ellenbergerite—a new mineral of the pelitic system—are stable. Experimental studies of the MgO-Al₂O₃-SiO₂-H₂O system have enabled the synthesis of Mg-carpholite, Mg-chloritoid, and pyrope, and the determination of their stability and phase relationships between 400 and 800°C, 15 and 40kbar. When applied to natural systems and combined with new dating results (³⁹Ar-⁴⁰Ar), these data are incorporated into an evolutionary model of the Alpine orogeny that involves the subduction of the continental crust to a depth of nearly 100 km
