Abstract

Utilizing the criteria of linearity and extensiveness of structural, lithologic and geomorphic features (as evident on the Tectonic Map of North America), it is possible to define in North America a series of northeast and northwest lineaments which resemble in distribution the theoretical, worldwide systematic shear pattern as defined by Vening Meinesz (1947) and later named the regmatic shear pattern by Sonder (1947).

East-west lineaments as well as extensive faults and lineaments parallel to the coasts of North America are also part of this crustal fracture system. North-northeast and north-northwest lineaments also occur, but are subordinate in expression to the above features.

Previous investigators of the regmatic shear pattern have suggested such possible origins as: drifting of the earth’s rotational poles with regard to the crust; contraction of the earth resulting in tangential pressures; meridional compressional forces generating a pure-shear system of mechanics.

The angles of intersection, however, between the northeast and northwest crustal fractures of North America are for the most part greater than pure-shear mechanics would produce. A possible cause of the North American pattern, more compatible with the observations, is a tensional origin produced by primordial, hemispheric coupling.

The east-west, the northerly trends and the coastal fractures are also probably of tensional origin, but are thought to have developed subsequent to the primordial northeast-northwest fracture system of North America.