Differentiation of melts under conditions of the upper mantle
© O.V. Usenko
Theoretical concepts developed in the paper are the base for the method to determine the depth of asthenosphere location by the composition of magmatic rocks. Concepts of petrology, geophysics as well as general and physical chemistry have been generalized, geodynamic and physical-chemical processes taking place during deep melts differentiation have been taken into account. Application of analogy of melt behavior under mantle PT conditions and electrolyte water solution under surface PT conditions has been proposed, which allows description in the first approximation of interactions between structural units of the melt. Subdivision of unbalanced process into succession of elementary stages permits to describe melt behavior in the categories of balanced thermodynamics. It has been shown that chemical composition of rock in the first approximation is determined by phase reactions in the melt under specified pressure and temperature. Chemical composition of the melt is determined by free Gibbs energy approaching to zero in the system with constant pressure and temperature, mineral composition of rock specified by the melt structure is determined by approaching to zero of free Helmholtz energy in the system of constant volume under specified temperature.