Komatiites probably form in extremely hot mantle plumes. Boninite magmatism is similar to komatiite magmatism but is produced by fluid-fluxed melting above a subduction zone.

Where do you find peridotite?

Peridotite is the dominant rock of the upper part of Earth's mantle. The compositions of peridotite nodules found in certain basalts and diamond pipes (kimberlites) are of special interest, because they provide samples of Earth's mantle brought up from depths ranging from about 30 km to 200 km or more.

Where are ultramafic rocks formed?

Many surface exposures of ultramafic rocks occur in ophiolite complexes where deep mantle-derived rocks have been obducted onto continental crust along and above subduction zones.