The physicochemical dynamics of evolution of fluid above asthenosphere systems beneath the Siberian Platform

A mathematical model is proposed for the two-velocity nonisothermal dynamics of the interaction between the convecting upper mantle and the multilayer lithosphere with local permeable zones. Based on the statistical processing of data on the bulk compositions of fluids from mantle rocks beneath the Siberian Platform (SP) and the Earth’s crustal metamorphic rocks of granulite and amphibolite facies, we discuss the problems of specifying the initial and boundary conditions for the description of the dynamics of convective melting in permeable zones above asthenosphere. To determine the nature of the established linear CO2–H2O trend (these are the main fluids of inclusions), we consider the 2D dynamics of formation of the T and P fields and the accompanying physicochemical dynamics of heterophase interaction between supra-asthenosphere magmatogene fluids and depleted rocks of the lithospheric mantle. The performed experimental and computational studies of the bulk composition and nature of the fluid phase in rock xenoliths from the SP lithosphere and Earth’s crustal metamorphosed strata showed that: (1) the gas phase of lower-crustal metamorphic rocks differ significantly in bulk composition from the gas phase of mantle lithosphere rocks, (2) about 80 % of the gas phase in the minerals of lithospheric mantle ultrabasites are oxidized products of the re-equilibration of supra-asthenosphere magmatogene fluids transformed in regional fault zones, (3) a periodic decompression of lithospheric mantle strata in the SP deep fault zones is the main factor of this re-equilibration, (4) data on the composition of the gas phase in primary inclusions in minerals of igneous rocks can be used to calculate the model composition of asthenospheric fluids.