ABSTRACT

It is possible to show by constructing simple model experiments that vertical uplift can produce first-order tectonic features similar to those seen in nature. Models of known tectonic features such as the orogen and tensional furrow are simulated by inflating and deflating a large elongate balloon beneath layers of clay and lime slurry. Symmetrical and asymmetrical orogens as well as simultaneous and migrational orogens are simulated. The simultaneous orogen forms as the result of the balloon inflating as a unit along its length. The migrational orogen is formed by the balloon progressively expanding along its length. The migrational expansion causes compressional folds to develop ahead of the expanding front while drag folds and wrench faults are formed along the flanks.

The first-order tectonic features of known areas are modeled by using simulated orogens placed in the same relative positions as the naturally occuring features. Some of the areas modeled are the Rocky Mountains, the California system, and the Central Western Hemisphere.

Transverse and extension faults are produced experimentally by vertical uplift. Offsetting uplifts of orogen models produce transverse faults as does differential uplift along the same model orogenic belt. The model transverse and extension faults compare favorably with those observed in nature.

A theory based on the model experiments of vertical uplift is advanced which relates the possible ballooning up of the upper mantle to tensional furrow development and transverse faulting. Uplift and cooling occur along previously established weak zones in the crust. It is possible that these weak zones were originally in the form of tensional furrows and transverse and extension faults. They were probably the result of previous orogenic episodes. The possibility exists that the current orogenic areas of the earth are presently causing the development of tensional furrows and transverse and extension faults. These zones of weakness may in time become the future orogenic areas of the globe.

A corollary to the theory is proposed which relates the transgressions and regressions of past geologic seas to the geographical distribution of the orogenic belts. It is possible that extensive tectonic activity along the oceanic ridge and rise areas causes transgression. During active periods the ridges and rises are distended and water is displaced from the ocean basins onto the continents. During times of great continental orogenic activity the oceanic areas are collapsed and regression occurs.

The conclusion is reached that model studies of vertical uplift can lead to many interesting speculations on crustal behavior.