Volcanic history reconstruction in northern Ecuador: insights for eruptive and erosion rates on the whole Ecuadorian arc
Résumé
In the northern Andes, the Ecuadorian arc presents a large number of Quaternary volcanoes, spread over a rather restricted area. The origin of this volcanic clustering is not well understood, and only a few chronological data older than the Holocene are available in northern Ecuador to document the arc development stages. In this study, we present new K-Ar ages obtained on lava flow and pumice samples for Cushnirumi, Mojanda, Fuya Fuya, Imbabura, Cubilche, and Cusín volcanoes, located about 40 km north of Quito, the Ecuador's capital city. Our results show that the volcanic activity in the northern part of the Ecuadorian arc started at least at ~ 1 Ma and that construction of volcanoes mainly occurred during the last 500 ka. Together with the radiometric data, numerical reconstructions of the paleomorphology of the volcanoes are used to estimate the volume of emitted magmas and the amount of eroded material in order to quantify their eruptive and erosion rates. Emission rates of Ecuadorian volcanoes range between < 0.2 and 3.6 ± 2.1 km3/kyr. Highest rates are obtained for volcanoes constructed over time periods shorter than 100 kyr by sporadic eruptive pulses, whereas lowest rates are calculated over longer periods that include quiescence phases. Erosion rates range between 0.02 ± 0.01 and 0.14 ± 0.09 km3/kyr and highlight that volcanic edifices whose activity ended recently are rapidly dismantled by physicochemical processes. Finally, the spatial distribution of Quaternary volcanoes as well as the spatio-temporal evolution of lava geochemistry may reflect the progressive influence of the Carnegie Ridge at depth.
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Licence : Copyright (Tous droits réservés)