Discussion
The mafic rocks high in both magnesium and silica concentration and are thought to be usually formed in fore-arc environments, typically during the early stages of subduction are called :
Answer: C
These rocks are boninites.
Boninites, named after the Bonin Islands south of Japan, are mafic volcanic rocks unusually high in both MgO and SiO2 but low in titanium. They form by melting of very depleted mantle wedge peridotite with added water, in fore-arc settings at the start of subduction, and are common in the lower parts of many ophiolites.
Komatiites are ultramafic lavas high in magnesium but low in silica, mostly Archean. Kimberlites and lamproites are volatile- and potassium-rich rocks from deep in continental mantle, not fore-arc magmas.
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