Peculiarity and consequence of geological subsurface water circulation

Abstract

The geological mass current of free and connected ground waters is estimated. This is where waters go under the continental crust during the processes of continental drift and subduction, form the hydrothermal systems, participate in volcanic eruptions, and constitute a descending current reaching the lowest part of the Earth’s crust and the uppermost mantle layer. The mass of this current, throughout the entire time of the tectonic process, is conducted, and a geological circle is carried out, amount ~0.95 × 10 24 g, and can be compared with the water mass contained in the mantle, which equals 1 × 10 24 g. The suggestion that the geological circle of ground waters is the mechanism for mantle dehydration compensation and keeping the water contained in the mantle at a level sufficient for convection to occur has been made. The most important peculiarity of ground waters in the Earth’s crust is that they are mobile components; i.e., virtually every system in the Earth’s crust is seen as an open one due to constant water transfer. Subsurface water transfer within the thickness of the Earth’s crust, determined by the combined influence of solar radiation and the thermal and gravitational fields of the Earth, occurs constantly during the process of crust evolution with a number of cycles, ranging from active water exchange in the uppermost crust to slow processes in the deep zones of the Earth’s crust. The refined quantitative model of subsurface water mass fluxes within the whole thickness of the Earth’s crust is shown in Table 1, which includes the following: (1) hydrogeological mass fluxes of free gravitational subsurface waters in active and slow water exchange zones of the continental block of the Earth’s crust which are totally controlling modern exogenic processes; (2) lithogenic metamorphic subsurface water mass fluxes in continental and subcontinental blocks of the Earth’s crust, determined mostly by release of physically connected waters in clayey strata being sunk and pressured, and also by sequential hydration of rocks, chemically connected water transfer, and dehydration of the former when sinking in the course of regional metamorphism; (3) geological lithospheric subsurface water mass fluxes in the oceanic crust, in the zones of crust adjunction with island arcs and active continental margins during the subduction process; these fluxes are formed by physically connected waters of the I seismic sedimentary layer of the oceanic crust and by chemically connected waters of the II volcanogenic and III basaltic layers of the oceanic crust. The geological role of free, chemically and physically connected waters, dragging under the continental crust in the course of continental drift and subduction; i.e., the geological subsurface water cycle with a total mass flux of 1.294 × 10 15 g/yr is extremely high. They generate hydrothermal systems, participate in volcanic eruptions, and form the descending water flux, reaching the lowest layer of the Earth’s crust and the uppermost mantle and equal to ~0.38 × 10 15 g/yr (Table 2). I.D. Ryabchikov [3] points out the high role of the geological cycle’s deep branches (down to 400 km), being able to the reach transit zone and control the beginning of mantle rock melting. The subsurface waters of the Earth’s crust, like the whole hydrosphere of the Earth, had passed the stage of protoplanetic substance degassing in their evolution. Contrary to other mobile components, the main part of the water mass did not leave the planet, and joined the Earth’s solid phase during degassing processes in the early stages of the planet’s development. The water content in the hypothetical primitive mantle is estimated by Ryabchikov [3] at ~0.1% of its mass, which is about 4 × 10 24 g. He also concluded that the H 2 O content in MORB glasses (190 g/t) corre