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Rejuvenated volcanism is a worldwide phenomena occurring on many volcanic oceanic islands in all of the major ocean basins (e.g., Samoa, Madeira, Mauritius). This plume-related volcanism follows the main edifice-building stage after a hiatus of variable duration (e.g., 0.6–2 Myrs in Hawai‘i). Hawaiian rejuvenated basalts typically have high MgO contents (>10 wt%) and carry upper mantle xenoliths. Thus, these magmas are assumed to have ascended rapidly through the crust. The basalts erupted along the Koko Rift in Honolulu, Hawai‘i are unusual in their large range in MgO (5.4–11.4 wt%), absence of mantle xenoliths and history of magma mixing. The Koko Rift is the youngest area of rejuvenated volcanism in Hawai‘i (67 ± 2 ka) and its best developed rejuvenation-stage rift system (15-km long rift with 12 major and several minor subaerial and submarine eruptive centers). Here we report on the first systematic petrologic investigation of the Koko Rift basalts to better understand this most recent example of Hawaiian rejuvenated volcanism. New textural and mineral chemical evidence indicates magma was stored along the rift and later mixed to produce the subaerial lavas with 10–11 wt% MgO. The lower MgO (5–6 wt%) subaerial lavas were probably byproducts of the initial hybrid magma, subsequent crystal fractionation and then a second magma mixing event. The absence of mantle xenoliths in Koko Rift lavas and the relatively moderate forsterite contents (84–85%) in the higher MgO lavas may be related to the development of a crustal magma system within the rift. The record of crustal magma storage and crystal fractionation, and two magma mixing episodes in the Koko Rift lavas is unique among Hawaiian rejuvenated volcanism.
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A possible sea-level fall trigger for the youngest rejuvenated volcanism in Hawaiʻi
Many intraplate oceanic islands undergo “rejuvenated” volcanism following the main edifice-building stage. Honolulu features Hawaiʻi’s most recent rejuvenated volcanism. K-Ar dating of Honolulu volcanism suggests that it started at ca. 750 ka and ended at <100 ka. Here, we present new 40Ar/39Ar ages and olivine diffusion modeling from Koko Rift lavas to resolve when the most recent Honolulu eruptions occurred and to evaluate possible mechanisms of rejuvenated volcanism and volcanic hazards. Diffusion modeling of olivine zoning profiles in Koko Rift basalts suggests that magmas were stored in the crust for many months prior to eruption. Six new 40Ar/39Ar ages cluster at 67 ± 2 ka (2σ), which demonstrates that Koko Rift is Hawaiʻi’s youngest known area of rejuvenated volcanism. The timing of Koko Rift eruptions coincides with the pronounced drop in global sea level (∼100 m) during Marine Isotope Stage 4. This major sea-level fall may have triggered the eruptions of Koko Rift magmas that were stored in the crust for months to years at < 15 km depth. The proposed mechanism is similar to that at other volcanic islands, which suggests that changes in global sea level may have significant control on the magnitude and frequency of eruptions at ocean island volcanoes.
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- Award ID(s):
- 1737284
- PAR ID:
- 10459972
- Date Published:
- Journal Name:
- GSA Bulletin
- ISSN:
- 0016-7606
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1130/B36615.1
