Geophysical Journal | 2007 volume 29 2

Physical-chemical processes within asthenosphere

© O.V. Usenko

PT conditions of melting and differentiation of melts in asthenosphere as well as physical-chemical interactions are considered which determine variability of magmatic rocks differentiated at the same (similar) depths. Comparison of results of experimental studies has been conducted, the probable reason of their divergence has been revealed - formation of chemically active components (O2- and CO, CO2) directly in the process of melting. Appearance of oxidized fluids and their interaction with crystal lattices of the mantle minerals influences the mantle composition and the ways of its differentiation. Location of a sthenosphere roof changes during activization - PT conditions of melt differentiation change. Increase of the degree of melting of the matter within the field of pressure gradient leads to formation of the layer with maximum degree of melting on the roof of asthenosphere. Here chemical reactions occur, which succession determines the consecution of appearance of exhalative and magmatic rocks on the surface as well as the haloes of fluid-thermal effects which are fixed as superimposed heating and metasomatic alterations of mantle rocks, which occur above asthenosphere. Redistribution of matter within the mantle takes place during activization and its partial emitting into the crust and on the surface. It is indicated by the change of geochemical specialization of the melts of final stages. Depleting of the mantle is the result of such a process - removal from it of both basaltoid component and active components- oxidized fluids, which are formed during the melting and differentiation, of halogens etc. It is fixed as alteration magm composition as well as exhalations of successive activizations. While melts of asthenospheric layer crystallize, reduction of residual oxidized fluids occurs as well as formation of metasomatic associations.

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