2014 GSA Annual Meeting in Vancouver, British Columbia (19–22 October 2014)

Paper No. 118-3
Presentation Time: 9:30 AM

WHAT'S DIFFERENT ABOUT HUALALAI, KOHALA AND LOIHI?


HARRISON, Lauren N., Pacific Center for Isotopic and Geochemical Research, University of British Columbia, 2020-2207 Main Mall, Vancouver, BC V6T-1Z4, Canada, WEIS, Dominique, Earth, Ocean and Atmospheric Sciences, University of British Columbia, Pacific Centre for Isotopic and Geochemical Research, 2020-2207 Main Mall, Vancouver, BC V6T 1Z4, Canada and GARCIA, M.O., Department of Geology and Geophysics, University of Hawaii, Honolulu, HI 96822

New high precision isotope data on Hawaiian basalts indicate the relationship between the structure of the Hawaiian plume and the geographically separated and geochemically distinct Loa and Kea trends is not as simple as the models (e.g. concentric vs. bilaterally zoned plume) would suggest. Both Loa and Kea compositional signatures occur at some volcanoes, regardless of their location on the Kea or Loa side1,2. We have analyzed samples from three such volcanoes: Hualalai, (6 shield, 2 post-shield), Kohala (18 shield), and Loihi (11 preshield) for Pb-Hf-Nd-Sr-Li isotopes and trace elements. Loihi is the only Hawaiian volcano currently in the preshield stage and is the only Loa trend volcano with Loa-like Pb and Li isotopes but transitional between Kea and Loa types in other isotopes and trace elements3. Kohala, with the most unradiogenic 208Pb/204Pb and 143Nd/144Nd of any Kea trend volcano, is the most Loa-like Kea trend volcano. Hualalai has the lowest 206Pb/204Pb at a given 208Pb/204Pb observed in Hawaiian post-shield lavas4, and the highest Li/Y ratio and lowest δ7Li of any oceanic island basalt5.

Hualalai and Kohala were the first subaerial volcanoes to form after a gap in volcanic activity between Maui and the Island of Hawaii. They also erupted during the largest upsurge in magmatic flux of the Hawaiian plume6,7. Higher magma flux does not necessarily translate into higher degrees of partial melting, as indicated by higher Ba/Y, Nb/Y, and La/Yb for Kohala lavas relative to other Hawaiian shields. In general, Hualalai, Kohala, and Loihi all have intermediate isotope and trace elemental compositions overlapping the Kea-Loa boundary. It is interesting to note that all Island of Hawaii volcanoes are characterized by a juxtaposition of both Kea and Loa trend characteristics in the same volcano, and the most extreme crossover volcanoes occur after a gap in volcanism between islands, i.e. Kauai, West Molokai, Waianae, Mahukona, and Kohala. Approximately 16% of Hawaiian shield samples “crossover” the Loa-Kea divide based on an analysis of radiogenic Pb (N=542).

1Xu et al. (2014) GCA, 132, 214-327. 2Marske et al. (2007) EPSL, 259, 34-50. 3Jackson et al. (2012) G3, 13(9). 4Hanano et al. (2010) G3, 11(1). 5Harrison et al. (in press) AGU Mono. 6Vidal & Bonneville (2004) JGR 109, B03104. 7Robinson & Eakins (2006) JVGR, 151, 309-317.