High temperature corrosion of olivine phenocrysts in Pliocene basalts from Banat, Romania

Pliocene trachy-basalts from the eastern Pannonian Basin in Romania were studied to re-evaluate their petrogenesis and establish a new model for their eruption characteristics. Bulk major and trace element concentrations, as well as Sr and Nd radiogenic isotope ratios confirm their OIB type signature, totally unaffected and unrelated to precursor subduction activities in the Carpatho-Pannonian region. Late stage magmatic high temperature corrosion of olivine phenocrysts was analyzed in detail, using high-resolution electron-microprobe techniques. The data indicate that corrosion occurred shortly prior to eruption, due to interaction of the magma with groundwater. The triggered variation in oxygen fugacity results in an oxi-hydroxylised modification of the original structure of the oli-vine, which, after eruption and contemporaneous degassing of volatiles, was overgrown by fresh olivine rims.