Progressive Glacial Retreat in the Southern Altiplano (uturuncu Volcano, 22°S) Between 65 and 14 Ka Constrained by Cosmogenic 3he Dating

This work presents the first reconstruction of late Pleistocene glacier fluctuations on Uturuncu volcano, in the Southern Tropical Andes. Cosmogenic 3He dating of glacial landforms provides constraints on ancient glacier position between 65 and 14ka. Despite important scatter in the exposure ages on the oldest moraines, probably resulting from pre-exposure, these 3He data constrain the timing of the moraine deposits and subsequent glacier recessions: the Uturuncu glacier may have reached its maximum extent much before the global LGM, maybe as early as 65ka, with an equilibrium line altitude (ELA) at 5280m. Then, the glacier remained close to its maximum position, with a main stillstand identified around 40ka, and another one between 35 and 17ka, followed by a limited recession at 17ka. Then, another glacial stillstand is identified upstream during the late glacial period, probably between 16 and 14ka, with an ELA standing at 5350m. This stillstand is synchronous with the paleolake Tauca highstand. This result indicates that this regionally wet and cold episode, during the Heinrich 1 event, also impacted the Southern Altiplano. The ELA rose above 5450m after 14ka, synchronously with the Bolling–Allerod.