The implications of foreland basins for the causative tectonic loads

Abstract

The geometry and development of foreland basins, being controlled primarily by flexure in front of ad- vancing orogenic wedges, contain information about these causative loads. Modeling of the flexure allows estimating the relations between basin width and depth and the taper angle of the orogenic wedges. These relations allow con- straining the advance of tectonic wedges and their taper an- gle based on the onlap of the basin fill and facies migration and on the thickness of the basin fill. Application of this approach to the Alps and the Acadian orogen of New England illustrates how the record of the as- sociated foreland basins can be used to constrain the history of orogenic wedges and their taper angle. The first case also allows to test this approach, while the second case demon- strates its application to a deeply eroded orogen. In these examples the basin records reveal that the orogenic wedges continued to advance and down-flex the foreland well after the exposed levels of these wedges experienced peak meta- morphism and deformation. The modeling also shows that during these late stages of loading of the foreland the oro- genic wedges maintained or even increased their taper an- gles, even though they were much eroded. As erosion tends to reduce the loads, it follows that concurrent modification of the deeper parts of the wedges must have taken place and compensated for the reduction of the load by erosion. Such inferences regarding the history of orogenic wedges, which can be deduced from the flexural interpretation of foreland basins, may be difficult to obtain otherwise, especially when the structure that existed during basin formation was much obliterated by erosion and modified by subsequent deforma- tion. This shows that integration of the insights that foreland basins provide regarding tectonic loads with information ob- tained from the interior of these loads can improve the un- derstanding of the evolution of mountain chains.