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SUMMARY The 2011–2012 eruption at Cordón Caulle in Chile produced crystal-poor rhyolitic magma with crystal-rich mafic enclaves whose interstitial glass is of identical composition to the host rhyolite. Eruptible rhyolites are thought to be genetically associated with crystal-rich magma mushes, and the enclaves within the Cordón Caulle rhyolite support the existence of a magma mush from which the erupted magma was derived. Moreover, towards the end of the 2011–2012 eruption, subsidence gave way to inflation that has on average been continuous through at least 2020. We hypothesize that magma segregation from a crystal mush could be the source of the observed inflation. Conceptually, magma withdrawal from a crystal-poor rhyolite reservoir caused its depressurization, which could have led to upward flow of interstitial melt within an underlying crystal mush, causing a new batch of magma to segregate and partially recharge the crystal-poor rhyolite body. Because the compressibility of the crystalline matrix of the mush is expected to be lower than that of the interstitial melt, which likely contains some fraction of volatile bubbles, this redistribution of melt would result in a net increase in volume of the system and in the observed inflation. We use numerical modelling of subsurface magma flow and storage to show under which conditions such a scenario is supported by geodetic and petrologic observations.
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Crystal mush interaction controls eruptive style during the 2018 Kīlauea fissure eruption
We use new geochemical, petrological, and rheological data to constrain the formation and emplacement of the highly compositionally unusual(andesitic basalt) Kīlauea 2018 Fissure 17 (F17) eruptive products. Despite the restricted spatial and temporal distribution, F17 samples are texturally and geochemically diverse. The western samples are enriched in SiO2 by up to 10 wt%, relative to their eastern equivalents; additionally, the western samples contain microcrystalline enclaves, absent from the homogenous eastern samples. The compositions erupted along F17 suggest interaction between the basaltic 2018 juvenile magma and a crystal mush at depth, likely a left-over from the nearby 1955 eruption. Magma mingling caused heating and local melting of remnant mush, leading to melt hybridization and volatile exsolution. Rapid water exsolution likely caused overpressurization of the reservoir underneath the western side of F17, leading to Strombolian explosions of viscous magma, in contrast to sustained Hawaiian fountaining on the eastern side. Remelting of remnant crystal mush and melt hybridization in open-conduit systems may hence be an effective mechanism in inducing volatile saturation.
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- Award ID(s):
- 2119838
- PAR ID:
- 10539935
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of volcanology and geothermal research
- ISSN:
- 0377-0273
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The 2018 LERZ eruption of Kilauea featured a wide range of eruptive styles. In particular, Fissure 17 (F17) displayed activity ranging from Hawaiian fountaining in the eastern part of the fissure to Strombolian explosions in the western part. Lava erupted from F17-West was highly viscous and contained magmatic enclaves. Magmatic enclaves have previously been observed in many other volcanic systems (e.g. Vulcano Island, IT and Sete Cidades Volcano, PT), where they have been attributed to injection of mafic magma into an evolved magma chamber, resulting in viscous fingering, quenching, and break-off into fragments. The F17 enclaves differ from previous studies in that the chemical compositions of the enclave and host magmas are very similar, and that the enclaves have a limited spatial distribution and lack signs of viscous behavior and quenching, pointing to a different formation mechanism than inferred for other volcanic systems. In order to test a different formation hypothesis, we conducted fractal analysis of the size distribution of 84 individual enclaves from F17-West lavas. Our results, including a fractal dimension of fragmentation Df of 2.59, indicate that the F17 enclaves likely formed by brittle fragmentation. Since the enclave and host magmas were at temperatures far above the glass transition during the magma hybridization, high strain rates have to be invoked to explain the brittle fragmentation. This may have caused the enclave magma to transition into solid-state behavior, allowing it to break off into fragments that were subsequently picked up by the host magma and carried to the free surface. The enclaves from F17-West therefore offer a unique insight into the diversity of processes that characterizes the shallow parts of volcanic systems, as well as the importance of strain rates in modulating the rheological behavior of magmas.more » « less
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