title: Source identification of volcanic ashes by geochemical analysis of well preserved lacustrine tephras in Nahuel Huapi National Park.
abstract: Well preserved volcanic ashes produced in recent events, recovered from sedimentary sequences extracted from three lakes belonging to Nahuel Huapi National Park, Northern Patagonia, were geochemically characterized in order to reveal patterns that allow the identification of the source. Two water bodies are situated in the direct impact area of volcanoes Calbuco and Puyehue-Cordón Caulle, while the third, lake Moreno, is situated in-between. The sedimentary sequences were dated by (210)Pb and (137)Cs techniques; the elemental composition was determined by Instrumental Neutron Activation Analysis. Distinctive patterns were found out when comparing glass shards, and also white pumice but in a lesser degree, of tephra layers extracted from lake Ilón, related mostly to volcano Calbuco events, and lake Nahuel Huapi (Brazo Rincón site), associated to Puyehue-Cordón Caulle eruptions. The geochemical parameters that showed decisive differences were SiO(2) and Na(2)O+K(2)O contents, the Eu anomaly, Rare Earth element ratios; the concentration of incompatible elements Cs, Rb, Th, Hf, Ta and Zr, and the compatible elements Cr and V. The six upper tephra layers extracted from lake Moreno showed geochemical patterns that allowed clear association with Calbuco and Puyehue-Cordón Caulle sources. These results set up the base for tephrochronological applications in historical periods in Nahuel Huapi National Park area.
authors.affiliation: Laboratorio de Análisis por Activación Neutrónica, Centro Atómico Bariloche, 8400 Bariloche, Argentina. romina@cab.cnea.gov.ar
authors.forename: Romina
authors.initials: R
authors.lastname: Daga
authors.forename: Sergio
authors.initials: S
authors.lastname: Ribeiro Guevara
authors.forename: María Lidia
authors.initials: ML
authors.lastname: Sánchez
authors.forename: María
authors.initials: M
authors.lastname: Arribére
mesh_terms: D001118:Argentina; D002588:Cesium Radioisotopes / Q000032:analysis*; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry*; D006207:Half-Life; D007856:Lead Radioisotopes / Q000032:analysis*; D018707:Volcanic Eruptions / Q000032:analysis*
chemical_list: D002588:Cesium Radioisotopes; D007856:Lead Radioisotopes