Tectonics, Climates, and Landscape Evolution of the Southern Central Andes: the Argentine Puna Plateau and adjacent Regions between 22 and 30ºS

Abstract

The history of the Puna Plateau and its marginal basins and ranges in the Eastern Cordillera and the northern Sierras Pampeanas structural provinces in northwestern Argentina impressively documents the effects of tectonics and topography on atmospheric circulation patterns, the successive evolution of orographic barriers, as well as their influence on erosion and sedimentation processes. In addition, this region exemplifies that there are several pathways by which tectonic activity may be coupled to the effects of climate and erosion. Apatite fission track and sedimentologic data indicate that distributed, diachronous uplift of ranges within the present Puna Plateau of NW Argentina began as early as Oligocene time, compartmentalizing a foreland region similar to tectonically active sectors along the current eastern plateau margins. However, fission track data from detrital apatite in sedimentary basins and vertical profiles along the eastern plateau margin document that wholesale plateau uplift probably affected this region in mid to late Miocene time, which may have been associated with mantle delamination. This coincided with the establishment of humid conditions along the eastern Puna margin and a sustained arid to hyper-arid climate within the plateau region. A common feature of the Puna Plateau is that its location corresponds to hyper-arid areas of the landscape in which channels fail to incise deeply into basin sediments or surrounding basement ranges. Importantly, the local base-level is hydrologically isolated from the foreland. This isolation occurs where the incising power of regional drainage systems has been greatly reduced due to a combination of diminished precipitation related to regional climate and local orography, and exposure of resistant bedrock. Hydrologic isolation of the plateau from the foreland permits deposition within basins as material is eroded from the surrounding ranges, reducing the relief between basins and adjacent peaks. While a variety of deformation styles and possibly combinations of different processes may have generated the high elevations observed in the Puna Plateau, the observed low-relief morphology requires evacuation of material via regional fluvial systems to be restricted. Therefore, the low-relief character of the orogenic plateau may be a geomorphic, rather than a tectonic phenomenon. At the eastern plateau margins similar basin histories can be observed in fault-bounded intramontane depressions that straddle the eastern Puna border. However, these basins remain only transiently isolated and internally drained due to their proximity to the high precipitation gradients which were established by orographic barriers in the course of Pliocene uplift. These outlying barriers focus precipitation, erosion, promote headward erosion, stream capture, and ultimately basin exhumation. This conspiring set of processes thus prevents these areas to become incorporated into the plateau realm, while the interior of the orogen conserves mass and may influence deformation patterns in the foreland due to high lithostatic stresses. Sustained aridity in the core of the orogen may thus be responsible for the creation, maintenance and potential for future lateral growth of the plateau, thus emphasizing the coupling between tectonics, climate and erosion.