Understanding the Timing and Extent of Glaciers in the El Tatio Geothermal Field During and Prior to the Last Glacial Maximum Using Cosmogenic Dating

Abstract

The Chilean Atacama-Altiplano, in the subtropical Andean Region, is an elevational plateau of >4000 masl, but the current annual precipitation is too low (e.g., <100 mm/yr) to sustain glaciers. However, geomorphic evidence including moraines indicates the past presence of alpine glaciers in the area. Previous studies exist in Chile and nearby Bolivia, but the datasets are still too limited to produce good glacial chronologies. Additionally, in South America and elsewhere, it is still uncommon to find dateable reconstructions of alpine glaciers before Marine Isotope Stage 2 (MIS 2 ~29 ka to 14 ka). In order to advance the understanding of past glaciations in the subtropical Andes, we collected 14 samples from andesite boulders of at least 3 well-preserved moraines from the El Tatio Geothermal Field in the Chilean Altiplano (~21-23॰S, ~68-69॰W). For constraining the ages, we utilized 3He cosmogenic dating in pyroxene, a well-established method, which is not a common practice for the subtropical Andean Region. Our results show at least three stages of glacial expansion in the El Tatio area ca. 22-30 ka (MIS 2), 58-59 ka (MIS 4), and 155-200 ka (MIS 6). Considering other glacial chronologies and paleoclimatic proxies in the Andes, our ages align well with climatic cold stages. Additionally, although prior research in other parts of South America have typically identified glacial expansions during MIS 2 and MIS 4, our data reveals evidence of a previously underexplored glacial expansion during MIS 6. Our research focuses on dating moraines in the arid, subtropical Andes, offering valuable insights into the timing and extent of glaciation, which can enhance paleoclimate reconstructions in the Southern Hemisphere. This work assists with future research on the local effects of glacial accumulation and retreat in and around the El Tatio Geothermal Field.