Abstract
Zircon and monazite ID-TIMS U-Pb dating of four Lower Ordovician altered ash-fall tuff beds (K-Bentonites) in NW Iberia provided coetaneous ages of 477.5±1, 477±1.3 Ma, 477.2±1.1 Ma and 477.3±1 Ma, with a pooled concordia age of 477.2±0.74 Ma. A conservative estimation of the volume and mass of the studied K-bentonite beds (using data from the Cantabrian Zone) returns a minimum volume for the preserved deposits of ca. 37.5 km3 (Volcanic Explosivity Index - VEI = 6, Colossal). When considering other putative equivalent beds in other parts of Iberia and neighbouring realms the volume of ejecta associated to this event would make it reach the Supervolcanic-Apocalyptic status (VEI=8, >1000 km3). Contrary to most cases of this kind of gargantuan eruption events, the studied magmatic event took place in relation to continental margin extension and thinning and not to plate convergence. We speculate that a geochronologically coincident large caldera event observed in the geological record of NW Iberia could be ground zero of this super-eruption.
Highlights
IOP PublishingLópez-Carmona Geology Department; Faculty of Science; University of Salamanca; Plaza de la Merced s/n, 37008, Salamanca, Spain
Volcanic supereruptions [1] are contemplated to be those that discharge magma in excess of 1015 kg, commensurate to a volume of more than 450 km3 [2,3] in a relatively brief period of time [4,5] with a Volcanic Explosivity Index (VEI) [6] commonly over 8
Published under licence by IOP Publishing Ltd. Few such eruptions are noticed in the geological record on account of: i) the odds of preservation are scant as the deposits they generate are eroded and ii) even if the deposits are perpetuated, they are challenging to recognize and reconstruct once they have been altered, deformed, metamorphosed and dismembered by ensuing geological events
Summary
López-Carmona Geology Department; Faculty of Science; University of Salamanca; Plaza de la Merced s/n, 37008, Salamanca, Spain
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