Endogenic Processes

geological processes associated with energy originating in the interior of the solid earth. Endogenic processes include tectonic movements of the crust, magmatism, metamorphism, and seismic activity (seeTECTONIC MOVEMENT; MAGMATISM; and METAMORPHISM). The principal energy sources for endogenic processes are heat and the redistribution of material in the earth’s interior according to density (gravitational differentiation).

The earth’s deep heat originates chiefly from radiation. The continuous generation of heat in the earth’s interior results in the flow of heat toward the surface. With the proper combination of materials, temperature, and pressure, chambers and layers of partial melting may occur at certain depths within the earth. The asthenosphere, the primary source of magma formation, is such a layer in the upper mantle. Convection currents may arise in the asthenosphere, and they are hypothesized to be the cause of vertical and horizontal movements of the lithosphere. In the zones of the volcanic belts of the island arcs and continental margins, the principal magma chambers are associated with superdeep dip faults (Zavaritskii-Benioff zones), slanting beneath the continents from the ocean side to depths of about 700 km. Under the influence of the heat flow or under the direct influence of the heat carried by rising abyssal magma, magma chambers form in the crust itself. Reaching the near-surface parts, the magma is intruded into them in the form of variously shaped intrusive bodies or is extruded onto the surface, forming volcanoes.

Gravitational differentiation has led to the stratification of the earth into geospheres of varying density. On the surface it is also manifested in the form of tectonic movements, which, in turn, lead to the tectonic deformation of crustal and upper mantle rocks (seeTECTONIC DEFORMATION). The accumulation and subsequent discharge of tectonic stresses along active faults causes earthquakes.

The two types of deep processes are closely interrelated: by lowering the viscosity of the material, radioactive heat promotes its differentiation, which accelerates the discharge of heat toward the surface. It is hypothesized that a combination of these processes leads to the temporal unevenness of the release of heat and light matter toward the surface, which, in turn, can be explained by the occurrence of tectonic-magmatic cycles in the history of the earth’s crust (seeTECTONIC CYCLE). The spatial irregularities of the same abyssal processes may explain the division of the crust into more or less geologically active regions, for example, into geosynclines and platforms.

Endogenic processes have been responsible for shaping the earth’s relief and the formation of many of the most important mineral resources.