PRO- VERSUS RETRO-PERIPHERAL FORELAND BASINS AS RECORDS OF OROGENESIS

Mountain belts are inherently asymmetric as a result of the dominant subduction of one lithospheric plate beneath another. Implications for the growth of mountain belts are well documented, but what it means for the development of foreland basins is poorly understood, thus limiting our ability to invert the signal. Here, we use a numerical model to simulate the growth of a doubly vergent thrust wedge over two flexed plates, one subducting beneath the other; the flexural depressions are infilled to capacity throughout to simulate foreland basin stratigraphy. The two modelled foreland basins are contrasted in terms of their subsidence histories, chronostratigraphic development, and overall stratigraphic architecture. The strong distinction between these basin types requires new terminology; we propose pro- and retro-peripheral foreland basins.

Pro-peripheral foreland basins are characterised by accelerating subsidence driven by both basin advection down the subducting plate, and outward growth of the thrust wedge. Their infill records onlap that approximates the plate convergence rate. They preserve the latest stages of orogenesis, but usually have a poor record of early mountain building. Well documented examples include the Appalachian basin, the North Alpine Foreland Basin, and the Ganges Basin.

In contrast, retro-peripheral foreland basins record linear to decelerating subsidence driven solely by the growth of the retro-thrust wedge. Consequently, once a mountain belt has achieved a steady state form, the tectonic driver of subsidence is switched off. A further consequence is that retro-peripheral basins primarily record the growth phase of an orogen, but have little stratigraphic record of steady state development. Additionally, the lack of active plate subduction means that the onlap of the cratonic basin margin is minimal, driven solely by the outward growth of the wedge. Examples of these basin types include the Aquitaine Basin, the Po Basin, and the South Westland Basin, New Zealand.