one of the two schools of thought in tectonics, based on the assumptions that the continents are immobile, or fixed, on the earth’s surface and that vertical tectonic movements played the principal role in the development of the earth’s crust. Fixism was one of the leading schools of thought in geology until the mid-1960’s, when the mobilist assumptions became widely accepted (seeTECTONIC THEORIES). Fixism is based on the hypotheses that plates, cratons, anticlinoria, and other sources of the denudation of terrigenous material develop lineally; that abyssal fractures exist for a very long time; and that magmatism of the same type is exhibited for a long time in similar regions.

Fixists, such as V. V. Belousov and the American scientist H. A. Meyerhoff, deny the mobilist assumption that horizontal movements of the large plates of the lithosphere are possible and postulate only insignificant horizontal movements (by a few dozen kilometers) of relatively small regions of the crust along overthrusts and strike-slip faults. The insignificant horizontal movements are assumed to result from vertical movements. A component of the fixist conception is the assumption that the formation of the ocean basins was a result of the subsidence of the crust without substantial extension but with transformation of the continental crust into a thinner oceanic crust (seeBASIFICATION). This assumption is opposed to the mobilist assertion that the formation of the ocean basins is a consequence of the moving apart of the continents.

According to the fixist theories, the major differences in tectonic conditions at the earth’s surface are determined by differences in endogenic conditions, that is, in conditions, within the earth.


Belousov, V. V. Osnovy geotektoniki. Moscow, 1975.


References in periodicals archive ?
The theory of fixism says that species are fixed, they do not evolve or devolve, and therefore the today's species are identical to the past species.
The querelle des analogues that was prompted by Geoffroy's theory of a single plan de composition is similarly too often analyzed as a confrontation between Cuvier's fixism and Geoffroy's evolutionism, since the latter's argument in fact keeps the Chain of Being model, an idea "itself based on an essential continuity throughout the animal kingdom" (Sommerset, 8).
Cuvier's aspirations are also divorced from the conservative religious stance often associated with his fixism and catastrophe theory.