New Mocho-Choshuenco explosive events identified in Laguna Carirriñe sediment cores, Northern Patagonia, Argentina

COTTET, JULIETA; VILLAROSA, GUSTAVO; OUTES, VALERIA

San Carlos de Bariloche

Congreso; IAL IPA 2022. Lakes, Memories of the Landscape; 2022

IAL-IPA

Mocho-Choshuenco Volcanic Complex (MCVC) is one of the most active volcanoes of the CSVZ during postglacial times, however its explosive record is poorly studied in Argentina. In order to improve the knowledge of its eruptive history and dispersion patterns east of the Andes, we studied a ̴ 7 m long lake sediment record from Laguna Carirriñe (SW volcán Lanín) spanning 12 ka. We identified several tephras of the E-NE driven plumes derived from the MCVC based on the analysis of tephra layers preserved in Carirriñe lake sediments and their correlation with tephras from Laguna Huaca Mamuil record (NE volcán Lanín) and nearby surface exposures. They are characterized by their glass morphology, geochemistry, mineral association, being the presence of framboidal pyrite a main characteristic that confirms MCVC provenance. We developed a Bayesian age-depth model to estimate the age interval of each described tephra.We identify the presence of 44 direct fallout events sourced from MCVC. The record includes the four largest eruptions previously reported: Neltume (white pumiceous rhyolitic tephra, 12.1-10.8 ka BP, VEI 5.7), Pirehueico (dacitic-rhyolitic glass, 9.2-8.4 ka BP, VEI 5.3) with a scoria layer at its base, Huilo (dacitic-rhyolitic with associated andesitic scoria, 8.4-8.1 ka BP, VEI 5.3), Enco (dacitic-andesitic fine ash, 1.5-1.4 ka BP, VEI 5); three new prominent tephras identified between Neltume and Pirehueico and two events between Pirehueico and Huilo eruptions. Another distinctive bimodal (rhyolitic/basaltic-andesitic) layer (996–931 yr BP), provisionally named Carirriñe Tephra, is identified in both, Carirriñe and Huaca Mamuil records. This layer is geochemically and morphologically characterised, and its NE dispersion is consistent with other prominent events identified within the Lago Carirriñe core. In addition, the ~9.5 cal. ka Chana tephra from Volcán Chaitén and several minor events derived from monogenetic cones sourced from MCVC are also identified in this high-resolution record.