Boninites: petrochemistry, systematics, and petrogenesis

Boninites are characterised by a great range of variety and they cannot be practically compared with igneous rocks like picrites, picrite-basalts, basalts, andesites, dacite, and rhyolites. This feature is conditioned by the presence of non-equilibrium phases: quarts-normative matrix and olivine impregnation. Abundance ratio and composition of non-equilibrium phases may be different, and that causes the variety of boninites. The boninite magmas were probably generated by the process of fractional crystallisation of high-magnesium picrite and picrite-basalt melts in subvolcanic conditions. It is necessary for the formation of boninites magmas that the eruption of magma was occurred at a definite stage of crystallisation before olivine separation.