Abstract

A fundamental abstraction in earth science has been the concept of a geotectonic cycle. It has gone hand-in-hand with various classifications of tectonic elements and has been intricately interwoven in geosynclinal theory. The basic scheme which has emerged is a progressive and somewhat deterministic sequence of events in space and time made up of three phases usually termed the geosynclinal phase, the tectogenic phase, and the orogenic phase. The geotectonic cycle has been equated with evolution of mountain systems and long considered a prime process in continental evolution.

The geotectonic cycle is examined in light of recent developments, including geosynclinal theory, studies in tectogenesis, and advances in submarine geology and geophysics. It is concluded that the concept of a geotectonic cycle is obsolete as a model of mountain system evolution, since definition of each of the so-called phases is obscure, relationship of any one phase to another is in doubt, and there is considerable evidence that the entire cycle can not be attributed to any single internal deterministic mechanism. Instead, the concept of multiple origins for mountain systems is suggested. Mountain complexes result from irregular successions of tectonic responses due to sea-floor spreading, shifting lithosphere plates, transform faults, and colliding, coupled, and uncoupled continental margins.

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