Dispersion and preservation of tephras in extra-Andean Patagonia associated with the H2 eruption of Hudson volcano during the late Holocene.

Abstract

In Patagonia, tephra deposits are associated with volcanoes from the Southern Volcanic Zone and the Austral Volcanic Zone of the Andean volcanic belt. Their spatial distribution is mainly influenced by the dominant westerly winds, dispersing and depositing the finest particles to the east of Andes, where arid climatic conditions prevailed during the Holocene. In this context, four sites located in southeastern Chubut were studied, where tephras preserved in deposits associated with ephemeral fluvial systems and dunes were identified and characterized, with evidence of local remobilization and primary deposition. The analyzed samples are mainly composed of a transparent vitroclasts population, accompanied by dark brown vitroclasts. Morphologies are typical of plinian phases, derived from bubble wall breaks in pumiceous fragments. Major-elements geochemistry of the volcanic glass indicated clustered compositions at the boundary of rhyolite-dacite-trachyte/trachydacite fields, consistent with the geochemistry recorded for the H2 eruption of Hudson volcano, whose dispersion was recorded to the E-SE. Also, radiocarbon dating of bones and charcoal associated with archaeological remains, recorded 40 cm below the layer, are consistent with H2 and give the tephra a maximum age between 3636 and 3882 cal. AP. In this way, H2 tephra can be considered a regional chronostratigraphic market of the Holocene in extra-andean Patagonia.