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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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Using Radiometric Dating, Magnetostratigraphy, and Tephrostratigraphy to Calibrate Rates of Hominin Evolution in the East African Rift
Age-calibration of hominin fossils and artifacts in the East African Rift is principally achieved through dating of associated volcanic-sedimentary strata. The dominant dating techniques for sites ≳100 ka are the 40Ar/39Ar radiometric dating method, magnetostratigraphy, and tephrostratigraphy. The 40Ar/39Ar technique relies on the occurrence of volcanic deposits in the target strata, which are often present as a consequence of the interplay of rift formation and volcanic activity. The frequency of datable material may be limited; however, by also applying the relative dating methods of magnetostratigraphy and tephrostratigraphy to these same strata, a chronostrati-graphic framework can be built and applied to fossiliferous strata. This chapter provides examples of the application of these techniques at Olduvai Gorge, Tanzania, and two areas of the East African Rift in Ethiopia.
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- Award ID(s):
- 2020044
- PAR ID:
- 10432598
- Date Published:
- Journal Name:
- Elements
- Volume:
- 19
- Issue:
- 2
- ISSN:
- 1811-5209
- Page Range / eLocation ID:
- 88 to 95
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.2138/gselements.19.2.88
