The evolution of the atlantic mega-undation : Causing the American continental drift

Abstract

Mega-undations are the largest class of deformations of the earth's surface, with diameters of many thousands of kilometers. They result from deepseated mass-circuits, probably in the inner mantle. Though their potential amplitude may be in the order of 100 km, their actual height is not more than some dozens of meters, because the arching up is partially compensated by sideward spreading of the earth's upper layers under gravity. By this process isostatic balance is more or less preserved.

If mega-undations occur in continental areas (such as Gondwana and Laurasia) new oceanic basins will open up on their top, with mid-oceanic ridges marking their crest; meanwhile relatively deep parts of the outer mantle rise to the oceanfloor. The overlying structural levels drift sidewards under gravity, towards the adjacent mega-undatory downwarps — like the spreading of a tilted stack of books. The highest unit i.e., the crust, advances farthest flowing (gliding) over the next deeper one (the “asthenosphere”). The deeper levels of the outer mantle (the “sclerosphere”) are also affected by these sliding movements, but their sideward displacement becomes less and less, and finally the lateral transport may become zero at the base of the outer mantle. This mechanism of continental drift occurs by means of the potential energy, which is present in every mass particle.

The wandering continental shield will show characteristic geotectonic phenomena at all sides; at the frontal side or “stem” geosynclinal subsidence (followed by orogenesis); at the rear-side or “stern” extension phenomena; along the “starboard” systems of right-lateral strike-slip faults will occur, whereas along the “port” left-lateral transcurrency is to be found.

These expectations (prognosis) of the working hypothesis are tested by the geotectonic analysis of a case history (diagnosis), namely the evolution of the Atlantic Mega-Undation and the corresponding drift-movements of the North American Shield. This geotectonic study provides strong converging evidence in support of the soundness of the undation theory; also in its application to the largest features of the earth known as mega-undations.