First cosmogenic ages for glacial deposits from the Plata range (33° S): New inferences for Quaternary landscape evolution in the Central Andes

Abstract

This paper presents the first numerical cosmogenic ages of glacial deposits from the eastern slope of the Plata peak (6000) in the arid Central Andes (32° S). The moraines are distributed along three different valleys: Vallecitos, Angostura, and Las Mulas. In the first, only one moraine was identified and no blocks could be sampled for dating. The other two have evidence of two glacial advances, Angostura I and Angostura II. The advances Loma de los Morteritos I and II were recognised in the Las Mulas valley. In both cases, first and second advances are preserved at a similar altitude. Surface boulders on the top of moraines were sampled for Be10. Obtained ages are all similar and Late Pleistocene in age. They fit very well with local stratigraphy and regional paleoclimate evidence. The Loma de los Morteritos moraine II located at 3000 masl dated to ∼25,000 years. Ages of ∼8,000 and ∼12,000 years were found for the Angostura II deposit (∼3300 masl). An age was obtained for the outwash deposit identified along the El Salto valley (∼69,000 years) associated with a Late Pleistocene drift. Quantitative datings presented here improve knowledge about the glacial chronology of the Plata range and Quaternary stratigraphy of the Central Andes, even though they represent a maximum age for these glacial advances. New findings support the occurrence of two Late Pleistocene glacial advances, and an older one in the Blanco River valley. Adjusted ages around ∼8,000 and ∼25,000 years for younger stage could be evidence of the Last Glacial Maximum (LGM) period for this region.