Melt Migration and Depletion-Regeneration Processes in Upper Mantle of Continental and Ocean Rift Zones

Tectonized harzburgites constituting the ultramafic basement of inter-arc and back-arc basins and forming the lower part of corresponding ophiolites provide textural and mineralogical evidences that some veins and other local mineral segregations resulted from crystallization from infiltrated basicultrabasic melt and the reaction of that melt with harzburgites. Veins of dunite are found by reaction. Veins of pyroxenite and gabbro may be formed by disequilibrium crystallization from infiltrated melts during the general cooling. These vein assemblages occur in many ophiolites including Upper Precambrian and Palaeozoic ophiolites of the Urals and southern Siberia.