Frozen Zone of the Lithosphere
Frozen Zone of the Lithosphere
discontinuous upper layer of the earth’s crust containing underground ice that is preserved for long periods of time (from two years to many millennia) in rock and soil; the upper part of the permafrost zone. The ice in the frozen zone of the lithosphere is present primarily as a rock-forming mineral that cements grains of the mineral and organic-mineral skeleton and determines the texture of permafrost rocks; it also often forms quite large, distinct bodies (lenses, veins, layers) or small, scattered accumulations of crystals in crevasses, cavities, and pores. Along with ice, the frozen zone of the lithosphere may contain the liquid phase of water as films of unfrozen, bound water and pockets of concentrated solutions.
The boundaries of the frozen zone of the lithosphere are determined by the distribution of underground ice and depend on a number of factors, including temperature, the porosity and moisture content of the rocks, the amount of impurities and dissolved substances in groundwater, surface forces, and pressure. Under subaerial conditions the upper boundary of the frozen zone of the lithosphere coincides with the bottom of the seasonally thawed layer; under glaciers and thin ice sheets it coincides with the boundary surface between surface and underground ice. In zones of hindered water exchange the lower boundary of the frozen zone of the lithosphere usually passes above the zero geoisotherm, that is, along the bottom of low-ice and fissured hard rocks (in folded mountain structures) or ice-saturated loose rocks (in platform regions); moreover, the underlying layers of the permafrost zone (with negative temperature but without ice inclusions) may be of great thickness (more than 1 km in the high latitudes). In zones of intensive water exchange the lower boundaries of the frozen zone of the lithosphere and of the permafrost zone usually coincide. The thickness of the frozen zone of the lithosphere varies from fractions of a meter in the weathering crust of mountainous areas to several hundred meters in the sedimentary beds of plains. The discontinuity of the frozen zone of the lithosphere is related either to the development of taliks or to the existence of conditions that prevent the formation of underground ice when there are negative temperatures.
The laws governing the distribution of the frozen zone of the lithosphere and its composition and structure depend on the set of morphostructural-morphosculptural, hydrological-climatic, geothermal, lithological-petrographical, and soil-geobotanical factors that determine the facies conditions of formation of frozen beds, as well as the beds’ iciness and texture, water and thermal regimen, and physical and mechanical properties. The development of the frozen zone of the lithosphere is controlled by heat exchange between the surface and the interior of the earth, the processes of sediment accumulation and denudation, and the interaction of surface water and groundwater. The peripheral areas of the frozen zone of the lithosphere (for example, on the West Siberian Plain) often do not correspond to the present-day distribution of average annual temperature on the earth’s surface, which is a premise for thermophysics analysis of paleogeographic schemata of the Pleistocene and paleoclimatic reconstructions.
The term “frozen zone of the lithosphere” was suggested in 1933 by the Soviet scientist N. I. Tolstikhin.
A. A. SHARBATIAN