[S-VC28] International Volcanology

[SVC28-02] Temporal Evolution of the Magma Supply System of Mentolat volcano, southern Chile

*Derek James Weller¹, Fidel Costa^2,3, Álvaro Amigo⁴, Jeffrey Oalmann^2,5 (1.National Institute of Advanced Industrial Science and Technology (AIST), Geologic Survey of Japan, 2.Earth Observatory of Singapore, Nanyang Technological Univeristy, 3.Institut de Physique du Globe de Paris (IPGP), Université de Paris, 4.Servicio Nacional de Geología y Minería (SERNAGEOMIN), 5.Univeristy of Tasmania)

Keywords:Mentolat, magma plumbing system, tephra, explosive eruptions, Chile

Mentolat volcano of the southernmost sector of the Andean Southern Volcanic Zone has produced at least 18 explosive eruptions over the last 18 ka. The petrology and geochemistry of 10 of the largest and regionally widespread eruptions were investigated to study the temporal evolution of the magma storage system feeding the explosive eruptions and the mechanism that could be triggering explosive activity at Mentolat. During the Late-Glacial period, Mentolat generated andesitic to dacitic products with unimodal plagioclase core compositions that were sourced from the middle crust (~11-15 km) and lacked clear evidence for magma mixing prior to the eruption. During the Early Holocene, the products were predominantly rhyolites, with bimodal plagioclase compositions, and mineral and glass textural evidence suggesting magma mixing and mingling prior to the eruptions. The melts from these eruptions were sourced from the upper- (4-7 km) and mid-crustal regions. From the Early Holocene up to the present time, the glass (rhyolitic to andesitic) and plagioclase core compositions are bimodal, the magmas from these eruptions were also sourced from the middle to upper crust, and textural evidence suggests that these two endmember glass compositions interacted prior to the eruption. For four of the eruptions, temperature estimates obtained from core and rim magnetite and ilmenite pairs indicate pre-eruptive reheating on the order of ~100-150 °C which could be a mechanism triggering the explosive events. The high crystallinity of the eruptive products and the presence of polymineralic crystal clots (plagioclase, amphibole, Fe-Ti oxides, ± apatite) indicates the presence of a crystal mush hot zone beneath Mentolat. These results indicate that magma mixing and resulting heat transfer may play an important role in triggering explosive eruptions at Mentolat. These findings suggest a mid-crustal source has been temporally invariant throughout the last approximately 18 ka with shallow magma sources being periodically tapped into since the deglaciation of the region.