Late Cenozoic topographic evolution of the Eastern Cordillera and Puna Plateau margin in the southern Central Andes (NW Argentina)

Abstract

The Andes constitute an important orographic barrier in the southern hemisphere, impacting atmospheric circulation, the amount and distribution of rainfall, and Earth-surface processes in a highly asymmetric manner. In the Central Andes of NW Argentina, the Andean Plateau (Puna) and the intermontane basins of the adjacent Eastern Cordillera constitute geological archives that furnish spatiotemporal information on surface uplift and associated paleo-environmental change. Today, rainfall in NW Argentina is focused along the windward flanks of the Eastern Cordillera, while its intermontane basins and the Puna constitute high-elevation regions with strongly reduced rainfall. The present-day influence of these topographic characteristics on precipitation patterns is reflected by systematic changes in the hydrogen stable isotope ratios of meteoric water. Proxy archives from basin strata record past environmental conditions and provide insight into the nature of topographic growth through time. We present 34 new hydrogen isotopic compositions of volcanic glass (δDg), extracted from tuffs interbedded with the sedimentary deposits of three different regions across the eastern Andean margin between ca. 24°S and 25°S latitude. Combined with new zircon U-Pb geochronology, our data show clear spatiotemporal variations in δDg correlating with topographic growth and ensuing orographic effects during the Miocene and Pleistocene. In particular, variations in δDg indicate that the Pastos Grandes (Puna) and the Toro (Eastern Cordillera) basins had attained modern elevations by ca. 8 and 6 Ma, respectively. A strong positive shift in the δDg record of the Toro Basin after 840 ka coincides with deposition of thick fluvial/alluvial conglomerates suggesting orographically induced aridification due to progressive range uplift to the east. Other δDg records from the Eastern Cordillera show similar, but diachronous events emphasizing the importance of regional tectonics for environmental change with implications for the formation of orogenic plateaus.