Chemical composition of ultrabasites and composing minerals from the Tonga Trench

The ultrabasites included harzburgites and dunites. Peridotites show clearly manifested material characteristics of ultrabasic relicts strongly depleted in low-temperature basaltic components.

It is suggested that they have arose in the high degree of partial melting (about 30%) of a matrix mantle source of the lherzolite type. Great similarity of the rocks studied with ultrabasites of many ophiolites that are widespread in folded belts indicates that young island arcs are among the most likely geodynamic environments of ophiolite generation.