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Petrology of Koko Rift Basalts: Hawai‘i's most recent and atypical rejuvenation stage eruptive sequence

Garcia, M.O.; Swanson, K.; Lormand, C.; Norman, M.D.

Authors

M.O. Garcia

K. Swanson

M.D. Norman



Abstract

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.

Citation

Garcia, M., Swanson, K., Lormand, C., & Norman, M. (2022). Petrology of Koko Rift Basalts: Hawai‘i's most recent and atypical rejuvenation stage eruptive sequence. Journal of Volcanology and Geothermal Research, 424, Article 107504. https://doi.org/10.1016/j.jvolgeores.2022.107504

Journal Article Type Article
Acceptance Date Feb 11, 2022
Online Publication Date Feb 22, 2022
Publication Date 2022-04
Deposit Date Feb 14, 2022
Journal Journal of Volcanology and Geothermal Research
Print ISSN 0377-0273
Electronic ISSN 1872-6097
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 424
Article Number 107504
DOI https://doi.org/10.1016/j.jvolgeores.2022.107504
Public URL https://durham-repository.worktribe.com/output/1213945