A uniformitarian approach to reconstructing orogenic belts
Nalan Lom, A.M. Celâl Şengör, Boris A. Natal’in, "A uniformitarian approach to reconstructing orogenic belts", Tectonics, Sedimentary Basins, and Provenance: A Celebration of the Career of William R. Dickinson, Raymond V. Ingersoll, Timothy F. Lawton, Stephan A. Graham
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Orogenic belts, the main factories of continental crust and the most efficient agents of continental deformation, are commonly extremely complex structures. Every orogenic belt is unique in detail, but they are generally similar to each other, having mainly been products of subduction and continental collision. Because of that common origin, they all share common functional organs, such as magmatic arcs, various back-arc and retro-arc features, and multifarious fore-arc environments, collisional sutures, etc. The modern orogenic belts usually display adequate detail about these organs, enabling us to identify them even when they are deformed or otherwise dislocated. In reconstructing now-disrupted orogenic belts, we are after one or more Ariadne’s threads to follow the original structure from one package of rock to another. The most prominent, laterally persistent, and easy-to-follow structures among the major orogenic features are the magmatic arcs. As they are the common expression of their subduction zones, they form linear or arcuate lines along the strike, and they usually move episodically inwards or outwards, being located behind sharply defined magmatic fronts. Present-day dating techniques provide high-resolution dates from magmatic rocks, and the migration of the magmatic front is easily detectable. They form the main Ariadne’s thread in orogenic studies. Where they are absent, the most helpful structures possessing lateral persistence are the now-deformed Atlantic-type continental margins and suture zones.
We chose two major fossil orogenic belts, namely, the Tethysides, and the Altaids, to emphasize the methodology of comparative anatomy of orogenic belts. There have been many theories regarding the evolution of these orogenic belts. However, they are either local, only dealing with a small portion of orogen, or they are in conflict with presently active processes. We underline the importance of magmatic fronts as reliable witnesses of the geodynamic evolution of major orogenic collages. This paper aims to disperse the mist upon the reconstructions of complexly deformed orogenic belts with the simplest possible interpretations that help us to form testable hypotheses that can be checked with a variety of geological databases.