Evidence for large compositional ranges in coeval melts erupted from Kīlauea's summit reservoir

Rosalind T. Helz; David A. Clague; Larry G. Mastin; Timothy R. Rose

doi:10.1002/9781118872079.ch7

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Evidence for large compositional ranges in coeval melts erupted from Kīlauea's summit reservoir

Rosalind T. Helz·David A. Clague·Larry G. Mastin·Timothy R. Rose

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Abstract

Petrologic observations on Kīlauea's lavas include abundant microprobe analyses of glasses, which show the range of melts available in Kīlauea's summit reservoir over time. During the past two centuries, compositions of melts erupted within the caldera have been limited to MgO = 6.3–7.5 wt%. Extracaldera lavas of the 1959, 1971, and 1974 eruptions contain melts with up to 10.2, 8.9, and 9.2 wt% MgO, respectively, and the 1924 tephra contains juvenile Pele's tears with up to 9.1 wt% MgO. Melt compositions from explosive deposits at Kīlauea, including the Keanakāko‘i (A.D. 1500–1800), Kulanaokuaiki (A.D. 400–1000), and Pāhala (10–25 ka) tephra units, show large ranges of MgO contents. The range of melt MgO is 6.5–11.0 wt% for the Keanakāko‘i; the Kulanaokuaiki extends to 12.5% MgO and the Pāhala Ash includes rare shards with 13–14.5% MgO. The frequency distributions for MgO in the Keanakāko‘i and Kulanaokuaiki glasses are bimodal, suggesting preferential magma storage at two different depths. Kīlauea's summit reservoir contains melts ranging from 6.5 to at least 11.0 wt% MgO, and such melts were available for sampling near instantaneously and repeatedly over centuries. More magnesian melts are inferred to have risen directly from greater depth.

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Source-reported bounding extent: 19.391477141932167° to 19.43243859897175° latitude; -155.30960083007812° to -155.23492813110352° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Rosalind T. Helz, David A. Clague, Larry G. Mastin, Timothy R. Rose. 2015-02-27. Evidence for large compositional ranges in coeval melts erupted from Kīlauea's summit reservoir. https://doi.org/10.1002/9781118872079.ch7

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