Offshore Record of Explosive Volcanic Eruptions in the Southern Part of the Panamá Basin During the Past 10 Myr: 2. Inferences About the Construction of the Northern Andean Arc and Regional Geodynamics

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.