A PALEOELEVATION HISTORY OF THE PATAGONIAN ANDES FROM HYDRATED VOLCANIC GLASS
To assess the topographic history of the Patagonian Andes, we constructed a water isotope record from hydrated volcanic glasses contained in Cenozoic sediments from sections at Lago Jeinimeni (Paleocene-early Eocene), Gran Barranca (Eocene-Miocene), and Lago Posadas (early Miocene), all located on the eastern side of the Patagonian Andes. We extracted glasses from these sediments and measured their H isotopic composition. The precipitation δD values reconstructed from those glasses for the Paleocene-Eocene samples were concentrated at values of -85‰, Eocene-Oligocene samples average -100‰, and early Miocene samples cluster around -110‰. This steady progression towards more negative water isotope values from the Paleocene to the Miocene implies that (1) the Patagonia Andes had a protracted history of mountain building that began well before the Miocene and (2) that history appears likely to have been one of gradual mountain building during that period.