THE ROLE OF SEDIMENTARY BASINS IN OROGENIC BELTS

Although ordinarily viewed as passive recorders, sedimentary basins are active participants in the dynamic evolution of orogenic belts. In addition to their sensitivity to the kinematics, magnitude, and style of deformation, synorogenic basins are integral to the construction of elevated continental plateaus. In practice, a fundamental tenet of basin analysis holds that sediment preservation is a measure of the accommodation (space) produced by tectonic subsidence. However, multiple studies in the North and South American cordilleras, Alpine-Himalayan belt, and accompanying hinterlands of associated fold-thrust belts, demonstrate that this principle fails to explain the temporal and spatial diversity of basin evolution, erosion, and sedimentation. For example, closed-drainage intermontane basins within thrust systems of the central Andes (Eastern Cordillera, Bolivia) and central to eastern Tibet (Lunpola, Nangqian-Yushu basins) record sediment accumulation in the absence of tectonic subsidence. At a regional scale, internal drainage in the hinterland basins of the Tibetan, central Iranian, and Altiplano plateaus, as well as the large intracratonic successor basins of central Asia, may drive >5-10 km of accumulation without appreciable tectonic subsidence. Conversely, in other orogenic settings, large-magnitude, low-angle normal faults imposing rapid hangingwall subsidence do not generate long-lived supradetachment basins. Notable examples occur within externally drained, orogenic interiors in central Peru (Cordillera Blanca detachment) and Tibet (South Tibetan and Kongur Shan detachments). In the case of hinterland plateau basins, an evolutionary model is proposed in which strong crustal regions initially undergo limited shortening while surrounding weaker regions are considerably uplifted, forcing internal drainage. Upon sediment accumulation, the strong crust partially resists flexural subsidence, leading to isostatic imbalance, a net increase in surface elevation by simple sediment ponding, and a low-relief plateau landscape. After protracted accumulation (>10-30 Myr), crust supporting the elevated plateau basin begins to lose strength, further promoting plateau growth through internal deformation, crustal thickening, and lower crustal flow under Airy isostatic conditions.