Old magma and a new, intrusive trigger: using diffusion chronometry to understand the rapid-onset Calbuco eruption, April 2015 (Southern Chile)

Abstract

In April 2015, an unpredicted rapid-onset eruption occurred at Calbuco Volcano, Southern Andes of Chile. This event consisted of two, sub-Plinian eruptions separated by a few hours. By analysis of Fe-Ti exchange between ilmenite and titanomagnetite crystals in samples of erupted material, we determine timescales of pre-eruptive heating experienced at the partially solidified chamber base and constrain the magma residence time for the bulk of the carrier magma. Analysis of the Fe-Ti oxide pairs from a sample retrieved from a pyroclastic density current deposit (Cal-160) shows that it was affected by a significant heating event (recording 70-220 °C of heating), while other collected samples did not record this late heating. This sample is interpreted to represent a piece of crystal mush located at the bottom of a prolate, ellipsoidal mush reservoir, mobilised < 4 days before the eruption by a triggering pulse of mafic magma considerably hotter than the typical magmatic temperature of the reservoir. Another two fall deposit samples (lapillus, Cal-149Tb and Cal-155) of the eruption are interpreted to represent resident, eruptible magmas that did not interact with any magma recharge immediately prior to or during the eruption. We infer that these magmas had been at eruption temperature for some years based on their extensively equilibrated Fe-Ti oxides.

The petrology of a hazardous volcano: Calbuco (Central Southern Volcanic Zone, Chile)

“…Glomerocryst designates a monomineralic or polymineralic assemblage of macrocrysts. Our petrographic observations agree with those previously described by Lopez-Escobar et al (1992), Lopez-Escobar et al (1995), Moreno (2011), Romero et al (2016), Arzilli et al (2019), Morgado et al (2019b) and Namur et al (2020). There is a gradual evolution in the mineralogy from the basalts to the andesites: olivine and plagioclase are the sole macrocrysts in the least differentiated sample (basalt CL119), the proportion of olivine relics surrounded by a peritectical rim apparently decreases with increasing SiO 2 , augite macrocrysts are rare or absent in the basalts, abundant in the basaltic andesites and again less abundant in the andesites, amphibole has not been observed in the basalt and is much more abundant in the andesites than in the basaltic andesites.…”

“…The tephra (0.27 ± 0.007 km 3 : Romero et al (2016); 0.38 ± 0.1 km 3 : Castruccio et al (2016); 0.58 ± 0.28 km 3 : Van Eaton et al ( 2016)) were essentially deposited on the northeastern part of the volcano and the finest ash dispersed across Chile, Argentina and Uruguay. They mainly consist of a basaltic andesite (Castruccio et al 2016;Romero et al 2016;Morgado et al 2019b;Namur et al 2020) with a high amount of crystals (35 to 65 vol. %), plagioclase, orthopyroxene and clinopyroxene being dominant.…”

Using Conceptual Models to Relate Multiparameter Satellite Data to Subsurface Volcanic Processes in Latin America

“…Deformation data were first available on 26 April 2007, and 28 cloud-free ASTER scenes were acquired before eruption. The triggering mechanism is believed to have been transient: fracturing during seismic events caused a network of cracks to become interconnected, which provided a conduit for a deep source magma to heat shallower magma bodies, triggering an eruption (e.g., Castruccio et al, 2016;Morgado et al, 2019;Wicks et al, 2011). It is unlikely that the current level of sensitivity of satellite data would be able to detect this process due to the source depth and limitations in temporal resolution.…”

The Temporal Variation of Magma Plumbing System of the Kattadake Pyroclastics in the Zao Volcano, Northeastern Japan

“…This may require keeping the two magmas in contact a certain time, during which they may allow chemical diffusion and facilitate magma mixing (Cooper 2018 [9]; Nishi et al 2019 [10]). The detailed petrologic examination of erupted mixed rock provides important information about the processes of the reactivation of the shallow chamber and mixing (Singer et al 2016 [11]; Morgado et al 2019 [12]).…”