The large eruption 4.2 ka cal BP in Cerro Blanco, Central Volcanic Zone, Andes: Insights to the Holocene eruptive deposits in the southern Puna and adjacent regions

Abstract

espanolLa erupcion del Complejo Volcanico Cerro Blanco en el sur de la Puna, noroeste de Argentina (4410–4150 a BP) se investigo para obtener nueva informacion sobre estratigrafia, geomorfologia, volcanologia fisica, dataciones por radiocarbono, petrografia y geoquimica. La caracterizacion de los productos en relacion a la evolucion de la caldera de Cerro Blanco permitio estimar la distribucion de los depositos de ceniza de la fase paroxismica Plineana de la erupcion. Estos novedosos resultados evidencian una gran erupcion explosiva riolitica que genero depositos cineriticos en un area de aproximadamente 500.000 km2, acumulando > 100 km3 de tefra (volumen total). Este ultimo valor supera el umbral inferior del Indice de Explosividad Volcanica (IEV) de 7. Los depositos de caida de ceniza cubrieron la region, llegando a mas de 400 km desde el Complejo Volcanico de Cerro Blanco, y los potentes depositos de flujos piroclasticos rellenaron los valles vecinos alcanzando una distancia de 35 km. Esta erupcion es la mas grande documentada durante los ultimos cinco milenios en la Zona Volcanica Central de los Andes y es probablemente una de las mayores erupciones explosivas holocenas del mundo. Ademas, se han identificado otras dos erupciones rioliticas en la region procedentes de otros dos centros eruptivos: una durante el Holoceno temprano y otra en el Holoceno tardio. La identificacion y caracterizacion de estos grandes eventos volcanicos proporcionan nuevas guias para los registros geologicos y arqueologicos regionales del Holoceno, siendo marcadores cronostratigraficos de aplicacion a una extensa area geografica de America del Sur. EnglishThe eruption of the Cerro Blanco Volcanic Complex, in the southern Puna, NW Argentina dated at 4410–4150 a cal BP, was investigated to produce new information on stratigraphy, geomorphology, physical volcanology, radiocarbon dating, petrography, and geochemistry. Identification of pre–, syn–, and post–caldera products allowed us to estimate the distribution of the Plinian fallout during the paroxysmal syn–caldera phase of the eruption. The new results provide evidence for a major rhyolitic explosive eruption that spread volcanic deposits over an area of ~500,000 km2, accumulating > 100 km3 of tephra (bulk volume). This last value exceeds the lower threshold of Volcanic Explosive Index (VEI) of 7. Ash-fall deposits mantled the region at distances > 400 km from source and thick pyroclastic-flow deposits filled neighbouring valleys up to 35 km away. This eruption is the largest documented during the past five millennia in the Central Volcanic Zone of the Andes, and is probably one of the largest Holocene explosive eruptions in the world. We have also identified two additional rhyolitic eruptions in the region from two other eruptive sources: one during the Early–Holocene and another in the Late–Holocene. The identification and characterisation of these significant volcanic events provide new constraints into regional Holocene geological and archaeological records, and offer extensive regional chronostratigraphic markers over a wide geographical area of South America.