From source to surface for small eruptive centres: using Sr–Nd isotopes and olivine diffusion timescales of the Fui Group (Chilean Andes)

The Fui Norte and Fui Sur small eruptive centres, together with the nearby Mocho-Choshuenco Volcanic Complex, are all located within what is potentially the most hazardous segment of the Southern Volcanic Zone of Chile. Developing comprehensive knowledge on the origin of evolution of these systems is not only important to better understanding of small eruptive centres, but also contributes to improved volcanic hazard prediction and mitigation. Using Sr–Nd isotopes, we determined that Fui Norte cluster has an independent plumbing system, while Fui Sur would be genetically related to the Mocho-Choshuenco stratovolcano. Through mixing models, we determined that the isotopic signatures of Fui Norte are closer to a MORB mantle isotopic composition, whereas the products from the Fui Sur cluster and Mocho-Choshuenco volcano exhibit a greater influence from slab components. This result shows that even in spatially constrained areas, magmas can record significant source differences. Using petrographic information and diffusion chronometry, we determined crustal timescales for the Fui Norte and Fui Sur SECs, from 1 month up to 4.5 years. This unexpectedly large time-scale range is interpreted as the lifespan of the crustal reservoir for these small eruptive centres. The significant differences in their source origin and the petrologic approaches reveal that both Fui Norte and Fui Sur have independent magmatic histories at the mid to upper crustal environment under similar timescales. Understanding that these systems operate independently from mantle to crust is relevant for future hazard assessment in the Southern Andes.