Metamorphic Processes in Rodingites of the Zermatt-Saas Ophiolites

Abstract

Abstract Three types of rodingites can be distinguished in the serpentinite complex of the Zermatt-Saas ophiolites based on mineral assemblages, texture, and chemical characteristics of bulk-rock and mineral compositions. These three types of rodingites show a genetic relationship on the basis of their mineral evolution. The mineral assemblage Czo-Hgrs-Chl-Di ± Uvr (rodingite I) was developed during ocean-floor metamorphism and represents the earliest rodingitic rock. A second phase of oceanic alteration is characterized by the formation of andradite-rich hydrogarnet. Subsequent progressive metamorphism resulted in formation of vesuvianite and continued formation of hydroandradite, producing the assemblage Hgrs-Vsv-Hadr-Chl-Di (rodingite II). The low-variance mineral assemblage Hadr-Vsv-Chl (rodingite III) represents equilibrium conditions, and the most completely rodingitized rock. Complex variation in chemical composition and mineral assemblages (i.e., distribution of rodingite) is the result of variation in protoliths and degrees of rodingitization.