Major crustal shears of North America, Europe, and Africa are shown and analyzed, and it is concluded that two orthogonal primary compressional shear sets, which are essentially wrench fault zones, exist world-wide. These sets are thought to have been generated by meridional and equatorial compressive stresses; the meridional and equatorial shear systems for the world are shown.

Major fault zones of the earth's regmatic shear pattern are considered to exercise fundamental control on orogenesis. These major fault zones probably extend downward to a discontinuity which may be the Mohorovicic discontinuity at the base of the crust, or may be deeper. It is thought that "continental drift" occurs by translation (with very little, if any, rotation) of the polygonal crustal blocks, which derive from the regmatic shear pattern, moving above this discontinuity. Ultimate driving forces are to be sought in relation to the earth's translation and rotation in space, and in sub-crustal (sub-Moho) convection currents; the result of these forces is omnipresent lateral compression in the crust.

Orogenesis results from the interaction of the crustal blocks as they move and yield in response to the lateral-compression stress field and the earth's gravitational field. On this basis, tectonic mountains are classified into: (a) linear uplifts with longitudinal wrench fault zones and related thrusting, (b) autochthonous fold belts, (c) vertically uplifted or tilted fault blocks, (d) domal uplifts, and (e) volcanic chains. Secondary effects of orogenesis include metamorphism and magmatic activity related to frictional heat from movement in major shear zones; and erosion, glaciation, and gravity sliding resulting from vertical components of movement along major faults.

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