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Constraints from source to surface: using Sr-Nd isotopes and olivine diffusion timescales in the Fui Group small eruptive centres (Chilean Andes)

Francisca Mallea-Lillo1 , Eduardo Morgado2, Lucy McGee1, Carl Spandler1, Miguel-Ángel Parada3,4

  • Affiliations: 1Department of Earth Sciences, School of Physics, Chemistry and Earth Sciences, University of Adelaide, SA 5005, Australia; 2 Escuela de Geología, Universidad Mayor, Manuel Montt 318, Providencia, Chile; 3 Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile; 4 Centro de Excelencia en Geotermia de los Andes (CEGA), Universidad de Chile, 803 Plaza Ercilla, 8370450 Santiago, Chile

  • Presentation type: Talk

  • Presentation time: Thursday 16:00 - 16:15, Room S160

  • Programme No: 3.7.6

  • Theme 3 > Session 7

Abstract

Small eruptive centres (SECs) located close to composite volcanoes are a common feature in the Southern Volcanic Zone of the Chilean Andes, and determining their level of connection is crucial to understand the magmatic processes in a small area comprising different styles of volcanism. Furthermore, determining the crustal pre-eruptive conditions and timescales can aid the assessment of volcanic hazards and describe the magmatic pathway for these SECs. The Fui Group Holocene SECs comprise two clusters: Fui Norte and Fui Sur, which are separated by less than 2 km and located next to the Mocho-Choshuenco volcano. Using Sr-Nd isotopes, we determined that Fui Norte cluster has an independent 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 Fui Sur cluster and Mocho-Choshuenco volcano have more influence of slab components. This result shows that even in very spatially constrained areas, magmas can show significant source differences. Using petrographic information and pre-eruptive conditions, we determined crustal timescales for the Fui Group, from 1-month up to 4.5 years. This unexpectedly large time-frame is interpreted to be the lifespan of the crustal reservoir for these SECs. The combination of chemical and petrographic approaches in the Fui Group show that the magma composition is controlled by the source composition, while the crystallisation history is associated to the crustal stalling and reservoir processes.