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Abstract Recharges of magma underneath basaltic volcanoes can occur as precursory events prior to an eruption but are not always revealed in geophysical data streams or erupted lavas compositions. In contrast, phosphorus within primitive, Mg‐rich (Fo89‐90), olivine can preserve recharge information lost by the mixed melt. Evidence of rapid growth and dissolution are preserved only in phosphorus X‐ray intensity maps, which reveal that Mg‐rich olivine from eruptions occurring between 2008 and 2020 at Kīlauea Volcano (Hawaiʻi) experienced at least two episodes of magma intrusion. We develop numerical diffusion models that evaluate the fidelity of the Fe‐Mg compositional archive by quantifying three factors that influence Fo population distributions: (a) the frequency at which an Mg‐rich basaltic liquid (in equilibrium with Fo90olivine) intrudes the reservoir, (b) the pre‐existence of a polymodal distribution of olivine crystal sizes and their shapes (c) the effects of sectioning on apparent olivine core compositions. We find that most crystals lose their initial Mg‐rich composition if they are held at temperatures relevant to summit magma storage conditions (1,160–1,190°C) for more than 10 years. Thus, previous assertions that Mg‐rich olivine crystals at Kīlauea are scavenged from centuries‐old stored magmas are unrealistic. Our method permits critical evaluation of contrasting explanations of heterogeneous Fe‐Mg contents of olivine cargo: (a) different total durations of mush storage with partial diffusive erasure of compositional traits, or (b) coexistence of multiple chemically distinct magmas. Our approach provides general guidance for the conservative interpretation of temporal information preserved within olivine Fe‐Mg compositional archives.
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A preliminary assessment of olivine phenocrysts from the monogenetic basalt of the McCartys Flow, Zuni-Bandera Volcanic Field, New Mexico
Monogenetic small-volume basaltic volcanoes are the most abundant subaerial volcanic landforms on Earth but are some of the most poorly understood systems. Their short durations, small volumes, and lack of recurrence make monitoring and hazard assessment difficult. The Zuni-Bandera volcanic field in western New Mexico contains small-volume basaltic centers erupting tholeiitic to alkalic basalts. Evidence shows no correlation of magma composition with eruption age, location, or volumetric output, prompting questions about the influence of magma ascent rates, magma storage conditions, and mantle source characteristics on lava compositions. Here, we present olivine major and minor element mineral chemistry from the 3200-year-old McCartys Flow, the youngest tholeiite basalt in the volcanic field. Olivine displays four phenocryst types with unique textures and major and minor element compositions. Multiple olivine types co-exist at the thin section scale. Major and minor element diffusion at frozen melt–phenocryst interfaces was modeled, revealing magma residence times ranging from 3–9 months. Type 3 olivine phenocrysts require step function initial conditions and record diffusion re-equilibration followed by magma mixing. These profiles indicate the magma resided in the reservoir for 10–15 years and accumulated from multiple batches of mixed magmas less than 10 days before the eruption. Our results show that primitive magmas in small-volume monogenetic volcanoes have complex lithospheric magmatic histories and stored in magma bodies influenced by an open system to develop different local chemical environments.
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- Award ID(s):
- 1828069
- PAR ID:
- 10299500
- Editor(s):
- Frey, Bonnie A.; Kelley, Shari A.; Zeigler, Kate E.; McLemore, Virginia T.; Goff, Fraser; Ulmer-Scholle, Dana S.
- Date Published:
- Journal Name:
- New Mexico Geological Society 72nd Annual Fall Field Conference Guidebook
- Page Range / eLocation ID:
- 141-152
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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