Mio-Piiocene glaciations of Central Patagonia: new evidence and tectonic implications.

• Yves Lagabrielle ^[1] ; Bruno Scalabrino ^[1] ; Manuel Suárez Dittus ^[2] ; Jean Francoise Ritz ^[2]
  1. [1] CNRS-UMR. Geosciences Montpellier
  2. [2] Servicio Nacional de Geología y Minería. Chile
• Localización: Andean geology: Formerly Revista geológica de Chile, ISSN-e 0718-7106, ISSN 0718-7092, Vol. 37, Nº. 2, 2010, págs. 276-299
• Idioma: español
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• Resumen

  • Patagonia is well known for spectacular occurrences of a variety of glacial-derived landforms and deposits and for a long history of ancient glaciations. In this paper, we frrst review the diverse evidence that demonstrates the development of glacial-related sedimentary units within the Central Patagonian Cordillera since 7 Ma. Well preserved glaciallandforms at the top surface of mesetas on both sides of the Lago General Carrera-Buenos Aires are described: the Meseta Guenguel to the north, and the volcanic Meseta del Lago Buenos Aires to the south. The latter meseta corresponds to a 3 Ma old, morphologically in verted paleo-piedmont, based on Ar/ Ar dates of the uppermost lava flows. It shows evidence of glacier advances to the NE direction. Over a distance of 20 km, glacial landforms observed by remote sensing data and digital elevation model define glacial tongues that were fed by the Cordillera reliefs to the west. These lobes are now beheaded from their westward sources along a morpho-structural corridor that bounds the Meseta del Lago Buenos Aires to the west. These remnants can be correlated with the oldest glaciallandforms recognized north of Lago General Carrera-Buenos Aires, on the Meseta Guenguel that form the Chipanque moraine system. From these features it is concluded that the glacial drainage network of Central Patagonia has been strongly modified following relief inversion in response to erosion processes and to tectonic causes. Changes occurred after 3 Ma, from a smooth piedmont surface covered by an extensive ice rnantle ending with ample glaciallobes, to the current series of deeply incised glacial valleys such as the Lago General Carrera-Buenos Aires depression. These new data bear important constraints on the history and development ofthe first glaciations in southem SouthAmerica.