HR: 0800h
AN: V51A-1473    [Abstracts]
TI: Unspiked K-Ar dating of the Koloa rejuvenated volcanism and shield Waimea Canyon Basalt on Kauai, Hawaii
AU: Tagami, T
EM: tagami@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
AU: * Sano, H
EM: sanoukun@kueps.kyoto-u.ac.jp
AF: Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto, 606-8502 Japan
AU: Garcia, M O
EM: garcia@soest.hawaii.edu
AF: Department of Geology and Geophysics, University of Hawai`i, Honolulu, HI 96822 United States
AU: Gandy, C E
EM: cgandy@hawaii.edu
AF: Department of Geology and Geophysics, University of Hawai`i, Honolulu, HI 96822 United States
AU: Blay, C
EM: cgandy@hawaii.edu
AF: TEOK Investigations, PO Box 549, Koloa, HI 96756 United States
AB: Rejuvenated Koloa Volcanics on Kauai is distributed extensively through the east and south of the island from more than 40 vents on the shield and postshield Waimea Canyon Basalt which composes most volume of the island. Unspiked K-Ar ages on groundmass in 23 samples from Koloa volcanics including lava from 12 traceable vents and five from late shield were determined in order to reveal the temporal distribution of rejuvenated vents and the length and timing of the quiescence and the rejuvenation. All samples dated were judged to be fresh mainly in thin section and partly in XRF analysis. The mass fractionation correction procedure, which is essential when samples have high atmospheric contamination, was applied in argon isotopic analysis for accurate dating. Our new K-Ar results show that the ages of Koloa Volcanics ranged from 0.15 to 3.85 Ma and that of late shield from 4.1-4.5 Ma. Ages of 3.95 Ma and 3.92 Ma were previously published from the end of shield volcanism meaning that very little time, at most ~0.1 m.y., intervened between the end of the Waimea Canyon Basalt and the beginning of the Koloa Volcanics. Our ages of Koloa Volcanics are composed of 0.15-2.1 Ma from 21 samples with no clear breaks, 2.5 Ma and 3.85 Ma, and a big gap exists between 2.5 Ma and 3.85 Ma. The new ages also reveal that one of the rejuvenated-stage vents, Kilohana, was active during separate two periods at least; 1.2 Ma and 1.5-1.6 Ma. These new results are inconsistent with the flexure-induced decompressional melting and convective mantle plume upwelling models for rejuvenated volcanism. They are more consistent with a lithospheric melting by conductive heating model, especially if small small convection has thinned the lithosphere.
DE: 1105 Quaternary geochronology
DE: 1115 Radioisotope geochronology
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005