A new regional compilation of the drainage history in southeastern Tibet suggests that the modern rivers draining the plateau margin were once tributaries to a single, southward flowing system which drained into the South China Sea. Disruption of the paleo‐drainage occurred by river capture and reversal prior to or coeval with the initiation of Miocene (?) uplift in eastern Tibet, including ∼2000 m of surface uplift of the lower plateau margin since reversal of the flow direction of the Yangtze River. Despite lateral changes in course due to capture and reversal, the superposition of eastward and southward draining rivers that cross the southeastern plateau margin suggests that uplift has occurred over long wavelengths (>1000 km), mimicking the present low‐gradient topographic slope. Thus reorganization of drainage lines by capture and reversal events explains most of the peculiar patterns of the eastern plateau rivers, without having to appeal to large‐magnitude tectonic shear.

Field observations, digital elevation model (DEM) data, and longitudinal profi le analysis reveal a perched low-relief upland landscape in the Red River region, Yunnan Province, China, which correlates to an uplifted, regional low-relief landscape preserved over the eastern margin of the Tibetan Plateau. As with other major rivers of the plateau margin, the Red River has deeply incised the lowrelief upland landscape, which we interpret to be the remnants of a pre-uplift or relict landscape. We examine longitudinal river profi les for 97 tributaries of the Red River. Most profi les consist of three segments separated by sharp knickpoints: an upper, lowgradient channel segment, a steeper middle channel segment, and a very steep lower channel segment. Upper channel segments correspond to the relict landscape and have not yet experienced river incision. Steeper middle and lower segments indicate onset of rapid, two-phase river incision, on the basis of which changes in external forcings, such as climate or uplift, can be inferred. In terms of two end-member scenarios, two-phase incision could be the result of pulsed plateau growth, in which relatively slow uplift during the fi rst phase is followed by rapid uplift during the second phase, or it could refl ect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth. Reconstruction of the paleo-Red River indicates ~1400 m river incision, 1400-1500 m surface uplift, and a maximum of 750 m vertical displacement across the northern Red River fault, elevating the northern Ailao Shan range above the surrounding relict landscape. On the basis of stratigraphic constraints, incision along the Red River likely began in Pliocene time.

No abstract

The style and mechanisms by which a foreland region is incorporated into an orogen depends on the tectonic style, effectiveness of uplift, and dynamic subsidence. Classical foreland-basin models refl ect a self-similar propagation of deformation into the foreland in a thin-skinned thrust-belt setting governed by wedge mechanics. Thick-skinned foreland regions, which are characterized by high-angle reverse-fault-bounded basement uplifts and intervening basins, however, do not fi t this idealized model. Unlike thinskinned tectonic provinces, deformation and uplift in these regions may be highly variable in time and space. Furthermore, deformation patterns may be complicated by the presence of preexisting structures, particularly those which lie at orientations that enable them to be reactivated and utilized to accommodated deformation under compression.The Neogene El Cajón-Campo del Arenal basin is one of a series of basins located along the eastern margin of the Puna Plateau within the Sierras Pampeanas, a region that is composed of a thick-skinned foreland fragmented by reverse-fault-bounded basement uplifts that regionally characterize an eastward-younging trend. This region is superimposed onto the Cretaceous Salta Rift province, which provides a series of preexisting structures that may potentially be reactivated. The basin is located along the eastern margin of the Puna Plateau, an integral component of the Andean orogen, which includes several fi lled, uplifted, and internally drained Cenozoic intraplateau basins. Structural and sedimentological similarities exist between basins along the margin of the Puna and those within it. Understanding the evolution of foreland basins, such as the El Cajón-Campo del Arenal basin, provides possible mechanisms for the development and incorporation of marginal basins into orogenic belts, and in the case of the Andean orogen, the potential for these basins to be incorporated into the plateau.Our analysis, which integrates seismic, sedimentary, and thermochronological data, characterizes the evolution of this basin and surrounding ranges. The appearance in the sedimentary section of a distinct grain-age population derived from the basement erosion surface constrains the uplift and erosion of an out-of-sequence intrabasin high to ca. 6 Ma. The basin fi ll, therefore, records an evolution from an undeformed foreland to one that is compartmentalized by basement uplifts and that is incorporated into the greater orogenic structure. The data reveal the importance of the reactivation of preexisting structures along the basin margin in creating east-dipping structures in a generally west-dipping domain. These opposing faults on the basin margin consequently caused the out-of-sequence uplift of the intrabasin range, the Sierra de Quilmes. The Sierra de Quilmes fragments the foreland and, because its position is locked by loads to the west and east, creates increased deformation within the basin, basin fi ll, uplift, and incorporation into the orogen. Unlike basins within the plateau...

No abstract