ZONES OF PLASTIC AND BRITTLE DEFORMATION IN A VERTICAL PROFILE OF THE LITHOSPHERE

The following main conclusions are drawn based on geological observations, investigation of the hydrodynamics of underground fluids during drilling of deep boreholes, experimental rock deformation at high temperatures, and seismic studies. On continents outside of subduction and riftogenesis zones, the transition zone between brittle deformation with hydrostatic pressure of the pore-fissure fluid and plastic deformation that predominates deeper is most commonly located at a depth of 9-13 km at the level of the geophysical boundary K1, not M. The fluid in crustal and mantle rocks below the consolidated transition zone is under full lithostatic pressure. During ordinary deformation at a rate of 10(-15) s-1 and less, continental sialic rocks at medium crustal depths are very compliant, flow plastically, and are suitable for hydraulic fracturing and development of magma intrusions and the formation of hydrocarbons. Below the K2 surface, rock viscosity begins to increase and then increases very sharply at the M discontinuity. At a temperature of 800-degrees-C beneath continental crust there is no lower strong layer of the lithosphere. Upper mantle rocks in oceans far from mid-oceanic ridges can have a strength to 1000 MPa and are stronger than continental rocks at the same depth.