Study of temporal and spatial variation of Hawaiian plume

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Here we summarize below our recent results of unspiked K-Ar dating on rejuvenated lavas from five Hawaiian volcanoes.(1) West Maui (Sherrod et al., in press) : Nine ages for the underlying postshield and 28 for shield stage units range from 1.8-1.3 Ma and 1.3-1.2 Ma, respectively. Therefore, the duration of volcanic quiescence prior to rejuvenation is about 0.6 m.y. at West Maui, much longer than estimated previously.(2) Koolau, Oahu (Ozawa et al., 2005) : New ages, on 41 samples from 32 vents of rejuvenated-stage Honolulu Volcanics and on eight samples of underlying shield-stage Koolau Volcanics show that shield volcanism ended at 2.1 Ma and that rejuvenated volcanism started at 0.8 Ma, resulting in a 1.3 m.y. hiatus in volcanic activity. Two distinct pulses were found for Honolulu volcanism at 0.8-0.35 and 〜0.1 Ma.(3) Kahoolawe (Sano et al., this meeting and submitted) : youngest eruptions left five small deposits of dike-fed cinders and sparse lava flows, which were previously undated but thought part of a rejuvenated stage on the basis of a substantial erosional unconformity. Two samples from the southernmost site and one sample from the next site northward show ages of 1.0 to 1.4 Ma, suggesting a short gap between the postshield and youngest eruptions.(4) Kauai (Sano et al., in prep.) : New ages of 23 samples from rejuvenated Koloa Volcanics range from 0.15 to 3.9 Ma, whereas ages of five samples from late shield-stage Waimea Canyon Basalt are 4.1-4.5 Ma. Hence, the volcanic quiescence before rejuvenation is at most about 0.3 m.y. The Kauai rejuvenated-stage can be divided into at least five eruptive pulses.