Search

Competing Interests: Competing interests statement:The authors declare no competing interest.

We present stable hydrogen-isotope analyses of volcanic glass ([Formula: see text]Dg) and radiometric ages (U-Pb zircon, U-Th calcite, AMS 14 C) from deformed sedimentary deposits in the vicinity of the intermontane Pocitos Basin in the central Puna of the Andean Plateau at about 24.5°S. Our results demonstrate 2-km surface uplift since the middle to late Miocene and protracted shortening that persists until the present day, while other sectors of the Puna show evidence for tectonically neutral and/or extensional settings. These findings are at odds with previous studies suggesting near-modern elevations (4 km) of the Puna Plateau since the late Eocene and formation of the intermontane Miocene Arizaro-Pocitos Basin associated with gravitational foundering of a dense lithosphere. Geophysical and geochemical data support the removal of continental lithosphere beneath the Puna, but the timing and mechanisms by which this removal occurs have remained controversial. We hypothesize that intermontane basin formation in the central Puna is the result of crustal shortening since about 20 Ma, followed by rapid surface uplift, likely related to lithospheric delamination.

Although Earth's climate history is best known through marine records, the corresponding continental climatic conditions drive the evolution of terrestrial life. Continental conditions during the latest Miocene are of particular interest because global faunal turnover is roughly synchronous with a period of global glaciation from ∼6.2-5.5 Ma and with the Messinian Salinity Crisis from ∼6.0-5.3 Ma. Despite the climatic and ecological significance of this period, the continental climatic conditions associated with it remain unclear. We address this question using erosion rates of ancient watersheds to constrain Mio-Pliocene climatic conditions in the south-central Andes near 30° S. Our results show two slowdowns in erosion rate, one from ∼6.1-5.2 Ma and another from 3.6 to 3.3 Ma, which we attribute to periods of continental aridity. This view is supported by synchrony with other regional proxies for aridity and with the timing of glacial ‟cold" periods as recorded by marine proxies, such as the M2 isotope excursion. We thus conclude that aridity in the south-central Andes is associated with cold periods at high southern latitudes, perhaps due to a northward migration of the Southern Hemisphere westerlies, which disrupted the South American Low Level Jet that delivers moisture to southeastern South America. Colder glacial periods, and possibly associated reductions in atmospheric CO 2 , thus seem to be an important driver of Mio-Pliocene ecological transitions in the central Andes. Finally, this study demonstrates that paleo-erosion rates can be a powerful proxy for ancient continental climates that lie beyond the reach of most lacustrine and glacial archives., Competing Interests: The authors declare no conflict of interest.