Glacial record and 36Cl cosmogenic dating in the Nevados de Chillán Volcanic Complex, Northern Patagonia

Andean landscapes contain key paleoclimate records of the Southern Hemisphere. However, many mountain regions in the Andes remain scarcely investigated in detail. In this study, we present an analysis of the Nevados de Chillán Volcanic Complex (NCVC), in Southern Chile (37ºS), aiming at unveiling the potential of this landscape to register past climatic conditions. This site is within a region of Temperate-Mediterranean climate transition (TMT; 35.5°–39.5°S), which comprises most of the Southern Volcanic zone (SVZ) of the Andes, that host the most active volcanoes of the cordillera, almost all of them are ice-capped. These volcanoes witnessed the multiple expansions and retreats of the Patagonian Ice Sheet (PIS) during Pleistocene glaciations and of smaller mountain glaciers during the Holocene, reflecting local climatic variations. Our findings show the NCVC preserves a recent and diverse glacial record, as identified with a detailed geomorphological mapping (1:20.000). The elevation and preservation of glacial deposits and scoured bedrock point to multiple glacial advances after the Last Glacial Maximum. Current analysis of ages obtained with 36Cl dating of andesitic boulders atop moraines support field observations and geomorphological interpretations, with different episodes from Early-Middle Holocene until the last centuries. The oldest measurements in could represent late glacial advances, which also occurred in central Andes and Patagonia. Ages from frontal moraines are coeval with the Little Ice Age, consistent with results of recent studies in adjacent volcanic areas. From lateral moraines dispersed age results suggest persistent glacial activity since the last millennia until 200 years ago. The younger ages are supported by historical accounts from 19th century that document glacial extent comparable with the location of sampled boulders. Overall, these results should be interpreted in light of uncertainties related to geomorphological mapping and especially with chronological constraints. Despite these limitations, the integrated approach adopted here provides a useful framework to identify regional-scale patterns of glacier fluctuations and to assess their sensitivity to climatic variability during the Late Pleistocene–Holocene.