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- Title
Preservation of Magma Recharge Signatures in Kīlauea Olivine During Protracted Storage.
- Authors
Mourey, Adrien J.; Shea, Thomas; Hammer, Julia E.
- 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 Fo90 olivine) 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. Plain Language Summary: Geochemical characterization of olivine crystals is a valuable petrological tool that provides clues into the composition of primitive (Mg‐rich) basaltic melts. Olivine from three recent Kīlauea eruptions (2008 and 2020 Halemaʻumaʻu lava lake at the Kīlauea summit, 2018 lower East Rift Zone) are analyzed for their iron (Fe), magnesium (Mg) and phosphorus (P) compositions. Analyzing concentration changes in slow diffusing elements like P in olivine and in fast diffusing elements like Fe‐Mg helps to understand growth, dissolution, and diffusive re‐equilibration cycles in the crystals. These cycles are inferred to have been caused by magma intrusions for all three eruptions. Then, we develop an interpretative framework that incorporates the disparate patterns of chemical heterogeneity revealed in the chemical maps of sectioned olivine crystals. Using numerical diffusion models, we evaluate how the frequency of Mg‐rich primitive intrusions, the size of the olivine crystals, and crystal sectioning affect the Fe‐Mg content within a given olivine population. We show that the variable compositions of olivine crystals erupted in Kīlauea lavas cannot result from remobilization of century‐old crystal mush. Key Points: Olivine crystals from three recent Kīlauea eruptions have sharp truncations in phosphorus zoning that mark olivine dissolution event(s)Dissolution‐recrystallization of high‐Fo olivine at Kīlauea can occur in less than a yearFo contents in Kīlauea olivine crystals reflects either a high frequency of magma recharges (>10 events/y) or short diffusion times (<5 years)
- Subjects
KILAUEA Volcano (Hawaii); OLIVINE; VOLCANIC eruptions; MAGNESIUM isotopes; MAGMAS; LAVA; IRON
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 1, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2022JB025523