High pressure coronites in the western Alps: a record of reaction pathways

This paper, after a short review on the historicai development of the use of the term «corona texture» to indicate a layered mineral structure developed at the contact between two reacting rninerals, describes methods and problems encountered in the study of coronitic rocks. Four well-known exampies of high-and ultrahigh-pressure coronitic rocks from the western AIps (Monviso and Zermatt-Saas concerning eclogitized ophiolites and Monte Mucrone and Dora Maira concerning eclogitized continental crust) are presented and discussed as case studies. It is stressed out that the study of coronitic rocks by means of classic microstructural and determination of chemical composition of reactants and products coupled with more recent thermodynamic modelling and mass-balance calculation enhance our understanding of reaction mechanisms, our knowledge of the role played by fluids and our ability to determine accurate P-T paths followed by rocks, involved in major tectonic processes.