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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.[Images not available. See PDF.]Graphical abstract

Volcanic material preserved in marine and lacustrine sediments is a key high‐resolution archive for studying the past eruptive history of volcanic regions. In this work, we use the geochemical and isotopic compositions of marine volcanic glass shards, the thicknesses, and age models of tephra layers preserved in the deep sediments of the eastern equatorial Pacific, to study their volcanic source, the long‐term evolution of volcanism, and its relationship with the regional geodynamics. We highlight that explosive eruptions associated with the Galápagos hotspot occurred in the Late Miocene and Early Pleistocene, which may reflect plume‐ridge interplays. We also show that the oldest products of the Northern Andean arc were deposited at ∼4.8 Ma, shortly before the extinction of volcanic activity in northern Peru‐southern Ecuador, due to the gradual flattening of the slab. The eruptive activity, apparently restricted to the Eastern Cordillera of Ecuador during the Pliocene, intensified and expanded from 2 Ma, with products of more varied compositions reflecting the construction of stratovolcanoes. This increase in volcanic activity, coeval with episodes of uplift of the Coastal Cordillera and with the development of the regional fault system that accommodates crustal deformations, may reflect the presence under the Ecuadorian Andes of the young Nazca oceanic crust, which carries the Carnegie Ridge. Finally, our results suggest that tephra of the Northern Andean arc recorded in sediments of the Panamá Basin were essentially emplaced by Plinian eruptions of a VEI‐5‐6 (Volcanic Explosivity Index), except one VEI‐7 caldera‐forming eruption, which occurred at 216 ± 5 ka.

Northern Andean volcanism is characterized by an intense Quaternary activity, whose onshore deposits have partly covered Mio‐Pliocene products associated with the early development of the arc, making it difficult to obtain an exhaustive catalog of past eruptions. To improve our knowledge of the largest eruptions that occurred in the Northern Andean arc, we analyzed several cores from drilling sites off Ecuador to seek tephra records. We characterize for the first time the mineralogical and geochemical characteristics of tephra beds recorded in the southern part of the Panamá Basin in the sediments of DSDP and ODP drilling Sites 504, 677, 678, 1238, 1239 and 1240. We show that products of at least 27 major eruptions from the Northern Andes have reached the Pacific Ocean since the Early Pliocene, and we have correlated 11 of them between several drilling sites. Products of the oldest volcanism had mainly rhyolitic compositions belonging to a High‐K calc‐alkaline magmatic series, whereas magmas display more heterogeneous SiO2 and K2O contents from the beginning of the Pleistocene. Correlations established in this work allow us to provide new temporal constraints to age models of sedimentary sequences of Sites 677, 1238 and 1240 constructed based on biostratigraphy. In addition, we show that sediments of ODP Site 1240, the closest to the Galápagos islands, recorded several Pleistocene rhyolitic eruptions associated with the hotspot's activity, possibly revealing past oceanic ridge‐hotspot interactions.

Tephra layers preserved in marine sediments are strong tools to study the frequency, magnitude and source of past major explosive eruptions. Thirty‐seven volcanoes from the Ecuadorian and Colombian arc, in the northern Andes, experienced at least one eruption during the Holocene. The volcanic hazard is therefore particularly high for the populated areas of the Andes and in particular cases for the coastal region, and it is crucial to document such events to improve hazard assessment. The age and distribution of deposits from major Holocene eruptions have been studied in the Cordillera, but no descriptions of distal fallouts have been published. In this study, we focused on 28 Holocene tephra layers recorded in marine sediment cores collected along the northern Ecuador—Southern Colombia margin. New lithological, geochemical and isotope data together with 14C datings on foraminifers allow us to determine the age and volcanic source of marine tephra, and to propose a first land‐sea correlation of distal tephra fallouts. We show that at least seven explosive eruptions from Guagua Pichincha, Atacazo‐Ninahuilca, Cotopaxi, and Cerro Machín volcanoes left tephra deposits recorded in marine cores over 250 km away from their source. Volume estimates of emitted tephra range between 1.3 and 6.0 km3 for the tenth century Guagua Pichincha, ∼5 ka Atacazo‐Ninahuilca, ∼6.7 and ∼7.9 ka Cotopaxi events, suggesting that they were eruptions of Volcanic Explosivity Index of 5. The distribution of these deposits also brings new constraints for a better evaluation of the volcanic hazard in Ecuador. Plain Language Summary During major explosive eruptions, large volumes of gases and tephra (lapilli and ash particles) are thrown into the atmosphere and can be spread by winds over 100 km and more. Tephra fallouts can impact the population, infrastructures and climate. It is therefore essential to document the age and magnitude of past major eruptions to better assess the volcanic hazards. In this study, we use the mineralogy, glass shard morphology, and the geochemical composition of tephra settled in marine sediments off Ecuador and Colombia to investigate their source. Thickness of tephra layers and radiocarbon ages performed on under‐ and over‐lying marine fauna allow us to determine the age of the eruptions, whereas the distribution of tephra yields constraints on the volume of fallout deposits. We show that the largest explosive eruptions from Ecuadorian and Colombian volcanoes reached the Pacific Ocean with a recurrence rate of about 1.5 events per millennium over the past 8 kyr. Key Points We propose a first land‐sea correlation of distal Holocene tephra off Ecuador based on 14C age and geochemical data Products from at least seven explosive Holocene eruptions in Ecuador and south Colombia reached the Pacific Ocean Volumes of tephra emitted by largest eruptions vary between 1.3 and 6.0 km3, suggesting they were VEI‐5 eruptions

The Ecuadorian arc is composed of an unusually high number of volcanoes, organized as along-arc alignments and across-arc clusters, in a relatively small area. Although several geochronological studies have been carried out in the last three decades, the eruptive history of the central zone of the arc remains poorly documented, preventing analysis of the initiation of volcanism of the whole arc. In this study, we present new K–Ar ages obtained from this central area, referred to as the Quito segment. These results were then incorporated into an updated comprehensive geochronological database of about 250 ages, allowing us to describe, at the arc scale, the spatial and temporal evolution of Quaternary volcanism in Ecuador. About eighty Quaternary volcanoes have been identified in the Ecuadorian Andes, 45 of which have been radioisotopically dated and/or identified as active or potentially active. The volcanic arc developed in three stages, characterized by an increase in the total number of active volcanoes. During the oldest Plio-Early Pleistocene stage, documented volcanic activity was mostly concentrated in the Eastern Cordillera of the Quito segment, with minor effusive eruptions in the southern Back-Arc. Since ~ 1.4 Ma, activity has spread to the surroundings of the Quito segment, and new edifices also appeared in the Western Cordillera and the Inter-Andean Valley. Towards the end of this intermediate stage (i.e., ~ 800 ka), volcanism occurred in isolated areas north and south of the Inter-Andean Valley. Finally, the late and current has been characterized by a remarkable increase in volcanic activity since ~ 600 ka. About 50 volcanoes were active during this stage. The spatial distribution of the Ecuadorian arc volcanism seems to be guided by deep mechanisms (i.e., slab geometry and age, amount and composition (fluids and melts) of slab input, mantle heterogeneities) and old crustal tectonic structures of the Western Cordillera, while neotectonics seems to influence the development of stratovolcanoes. In addition, we note that the spatial and temporal evolution of volcanism highlights the influence of the Carnegie Ridge and the young Nazca crust on the thermal regime of the subduction system, which in turn increases of volcanic activity in Ecuador.