Olivine growth rates in a tholeiitic basalt: An experimental study of melt inclusions in plagioclase

Abstract Basaltic glass inclusions trapped in plagioclase phenocrysts (An 84 ) are remnant of their parent magmatic liquid. They can be used as natural reactors for the experimental investigation of olivine growth rate as a function of temperature. The growth of one olivine nucleus can be observed at constant temperature. Supercooling from 15° to 150°C have been investigated. Growth habits vary from equant to feather in qualitative agreement with previous studies. Growth rates vary from −10 m s −1 to 6·10 −7 m s −1 ; they vary with the direction, the growth process (planar or dendritic) and the degree of supercooling. Chemical analysis of crystal overgrowth and the remaining liquid composition enables a mass-balance calculation which confirms the rates determined optically. The small number of results obtained so far does not permit to draw inferences on the growth mechanisms.