Possible physicochemical facies of wehrlitization of ultramafic rocks in the mantle wedge under volcanoes of the Kuril–Kamchatka frontal zone

A quantitative model describing the dynamics of the process of metasomatic wehrlitization of ultramafics is put forward. It is elaborated for the process taking place in permeable fault zones over a time span of 50 kyr with fluid source depths in the range of 150–50 km at initial temperatures of 1000–1200°C. The possibility of existence of two physical–chemical facies of this process has been demonstrated: one occurs at the level of garnet and the other is at the level of spinel depth facies. Their realization is related to the dependence of the activity of Mg–Ca–Si metasomatism against variation in the composition of low–molecular hydrocarbons in a fluid under conditions of changing T and P in a system.