EDUARD SUESS' ONE-SIDED PUSH: MECHANICAL NONSENSE OR GEOLOGICAL TRUTH?

A fundamental idea in Eduard Suess' (1831-1914) theory of mountain-building was that of one-sided push. He was criticised for not having understood the most basic idea of Newton's mechanics, according to which every applied force instantly creates a counter-force. Suess was the first geologist to study all the major mountain ranges of our globe from a structural geological viewpoint and to show that almost all have an asymmetric structure. Before him the Rogers brothers and J. D. Dana had guessed the same on the basis of their studies of the Appalachians, but they had not studied all the mountains of the globe. The precise mapping of the Rogers brothers in the Appalachians had shown that northwest-vergent folding and thrusting died away in the same direction and a decoupling of the folding layer from its basement was necessary to create the asymmetric mountain architecture observed. Their interpretation was found absurd and recourse was taken to Sir James Hall's earlier interpretation in terms of shortening similar to that between the jaws of a symmetric vise. The geosynclinal theory provided comfort to this interpretation. Suess' theory of mountain structure showed already in the beginning of the twentieth century that all mountains are fundamentally decollement structures above an underthrusting foreland and that is why they are asymmetric. The rise of plate tectonics eventually showed that subduction is the main decollement and that it necessarily imparts an asymmetric structure on all orogenic belts. The top of the subducting oceanic lithosphere (or of the underthrusting continental lithosphere in collision zones) represents the main detachment horizon and the prow of the upper plate functions as the piston that creates the one-sided push. This one-sided push gradually loses its force on the detachment, because the resistance to deformation is distributed on the entire detachment surface and that is why the deformation dies away from the piston, thereby creating an asymmetric mountain range. This new outlook on Suess' interpretation not only allows us to understand his overall tectonic viewpoint better, but also shows us what the real problem was the Rogers brothers were trying to solve in the Appalachians with their theory of wave propagation in a fluid substratum caused by gigantic gas explosions to the southeast of the mountain range.