Fig. 1

The stability field of zoisite and epidote. Reaction lines in violet are for zoisite relations in the model system CaO-Al₂O₃-SiO₂-H₂O (CASH). Boundaries in red represent schematically the displacement of the maximum extent of epidote in mafic and intermediate bulk compositions as a function of CIPW normative anorthite content, An. Bold numbers indicate anorthite contents in weight percent from studies that synthesized epidote (circles; An = 48–58: Thompson and Ellis 1994; An =71: Wittenberg et al. 2003) or defined an epidote-out reaction (An = 31: Poli and Schmidt 1995; Schmidt and Poli 1998; An = 23: Forneris and Holloway 2003, broken bold line). Experiments performed on a Mg-rich andesite, with An =15 (Poli and Schmidt 1995), did not result in the presence of epidote, pointing to a low-pressure stability of epidote in such composition. Dashed line represents the wet solidus after Kessel et al. (2005), black dot stands for the second critical endpoint