TECTONICS AND CLIMATE OF THE ARGENTINE PUNA PLATEAU AND ADJACENT REGIONS

The history of the Puna Plateau and intramontane basins along its E margin documents the effects of tectonics and topography on atmospheric circulation, the successive evolution of orographic barriers, and the link between tectonism and surface processes. Apatite fission track and sedimentologic data indicate that distributed and diachronous uplift of ranges within the present plateau began during the Oligocene, breaking a foreland similar to tectonically active sectors along the E plateau margins. However, paleosols, sedimentary facies, and stable carbon isotopes in intramontane sedimentary basins along the plateau margin suggest that wholesale plateau uplift may have affected this deformed region in late Miocene time coinciding with inferred mantle delamination (Kay et al. (1994), formation of an orographic barrier, and by a dramatic change from dry to humid conditions along the E plateau. The necessary conditions for the onset of the South American monsoon were thus established at that time. The changes at the plateau margin serve as proxy indicators for plateau uplift and creation of extensive, high-surface elevation area, which attracts easterly moisture. In contrast, aridity prevailed in the plateau and farther W. While combined different processes may have generated the high elevations of the Puna, the low-relief morphology is related to hydrologic isolation, coalescence of basins by overfilling, reduced incision, and exposure of resistant bedrock in an arid environment. The low-relief character of the orogenic plateau may be a geomorphic, rather than a tectonic phenomenon. Protracted aridity in the internal sector of the orogen has thus aided to create and maintain the high, internally drained landscapes of the central Andes. In contrast, headward erosion, stream capture, and ultimately basin exhumation govern the marginal basins, thus preventing these areas to become incorporated into the plateau realm and slowing lateral plateau growth.