Decompaction of metamorphic rocks under thermodynamic conditions of the Earth crust (experimental data)
Keywords:density of rocks, thermodynamic decompaction, pressure, temperature, velocity—density, modeling
A connection velocity—density inherent to the rocks of deep crust horizons is widely used while plotting concordant model of the Earth lithosphere with the methods of complex interpretation of geophysical data seeking for concordance of rated wave and gravity fields with the observed ones. Materials of experimental studies of elastic-density parameters of rocks under different thermobaric conditions of experiments, in particular, the values of density given in this work, complement and readjust information known before on relations of velocity and density of rocks at different depths considerably. Complex dependences ρ=f (РТ) have been shown for the first time with the areas of density inversion identified — thermodynamic decompaction of rocks, which have to be taken into account in petro-density thermobaric modeling of deep horizons of the earth crust. Zones of decompaction of lithosphere mineral material quite probably exist under present-day thermobaric conditions in the earth crust at the depth 5—15 km, they are characterized by decrease of density up to 0,02 g/cm3 and can produce horizons from 5 to 10 km thick. Rock decompaction is as a rule connected with structural transformations of substances stipulated by opposite per se phenomena of alteration of voluminous temperature expansion of minerals and their compressibility under thermobaric conditions of corresponding depths. Horizons of decreased density (by experimental data) as zones of low seismic velocities are sensitive to temperature regimes of the earth crust. While deep thermal flow increases density of rocks decreases, their ability to decompaction arouses, their permeability and absorbability rise, i.e. the process of mixing of fluids becomes more active and, as a result, metamorphic transduction of rocks takes place. In other words, zones of decreased VP and ρ are the most active horizons of contemporary geologic-geophysical transformations of mineral medium of the earth crust. Their availability may be criteria for search of mineral deposits because they are the most permeable for migrating mineral media in the earth crust.
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