Boninite is an extrusive rock high in both magnesium and silica, thought to be usually formed in fore-arc environments, typically during the early stages of subduction.
Boninite typically consists of phenocrysts of pyroxenes and olivine in a crystallite-rich glassy matrix.
Boninite is defined by Most boninite magma is formed by second stage melting in forearcs via hydration of previously depleted mantle within the mantle wedge above a subducted slab, causing further melting of the already depleted peridotite.
The second melting event is partly made possible by hydrous fluids being added to the shallow hot depleted mantle, leading the enrichment in large ion lithophile elements in the boninite.
Enrichment in Ba, Sr and alkalis may result from a component derived from subducted oceanic crust.