HR: 0800h
AN: V51A-1468    [Abstracts]
TI: Origin of the Honolulu Volcanics Series (Oahu, Hawaii) From High Precision Pb Isotope Data
AU: * Fekiacova, Z
EM: zuzana@mpch-mainz.mpg.de
AF: Max-Planck-Institut fuer Chemie, Abt.Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: Abouchami, W
EM: wafa@mpch-mainz.mpg.de
AF: Max-Planck-Institut fuer Chemie, Abt.Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: Galer, S J
EM: sjg@mpch-mainz.mpg.de
AF: Max-Planck-Institut fuer Chemie, Abt.Geochemie, Postfach 3060, Mainz, 55020 Germany
AU: Garcia, M O
EM: garcia@soest.hawaii.edu
AF: Dept. of Geology & Geophysics, Univ. of Hawaii, 2525 Correa Rd., Honolulu, HI 96822 United States
AB: The origin and sources of rejuvenated volcanism in Hawaii has been long debated with the depleted isotopic features commonly attributed to assimilation of the 110 Ma-old Pacific oceanic lithosphere underlying Hawaii. Alternatively, it has been recently suggested that this depleted component is a long-lived feature intrinsic to the Hawaiian plume [1, 2]. Here, we report triple-spike Pb isotope data on lavas erupted from the different evolutionary stages of Koolau volcano, including the rejuvenated Honolulu Volcanics Series (HVS), the main shield stage lavas, sampled by the Koolau Scientific Drilling Project (KSDP) and late-shield Makapuu subaerial lavas [3]. These data demonstrate the existence of compositional source variations throughout the evolution of the volcano. In addition, we obtained new Pb isotope data on basalts from ODP Site 843, located 225 km southwest of Honolulu which sampled 110 Ma-old Pacific crust. If these data are representative of the local oceanic crust and mantle, then the Hawaiian Pacific lithosphere is not a viable source component for the rejuvenated Honolulu Volcanics. Despite a narrow range in Pb isotope ratios, both the KSDP and HVS lavas define linear isotope arrays in Pb isotope space. While the two arrays have distinct slopes in ²⁰⁸Pb-²⁰⁶Pb space, suggesting the involvement of at least three Pb components, the two datasets overlap in ²⁰⁷Pb-²⁰⁶Pb space due to the extremely limited variation (< 1per mil) in ²⁰⁷Pb/²⁰⁴Pb ratios. By comparison, ODP site 843 basalts have significantly more radiogenic Pb isotopic compositions and form a linear Pb isotope array distinct from that of the HVS, although lying within the field of present-day EPR MORB [4]. Thus, there appears to be no major differences in the Pb isotopic character of ''old'' vs. ''young'' Pacific MORB. We infer that three distinct Pb components were involved in the source of Koolau: (1) an EM-type component, corresponding to the so-called ''Koolau component'', predominantly sampled by subaerial Makapuu lavas but recurrent in the main shield lavas, (2) a radiogenic Pb component, similar to the ''Kea-lo8'' of [5] common to the main-shield (KSDP) and HVS lavas, and (3) a depleted component unique to the rejuvenated HVS. The relatively uniform isotopic compositions of this ''depleted'' component (low ⁸⁷Sr/⁸⁶Sr, high ¹⁴³Nd/¹⁴⁴Nd) and, particularly its Pb isotopic composition, definitively rule out any involvement of Pacific lithosphere in the HVS. We conclude that the Hawaiian ''rejuvenated depleted'' component is intrinsic to the Hawaiian plume, probably thermally entrained by the upwelling plume during its ascent [6]. 1. Frey et al. Geochem. Geophys. Geosyst., 6(1), (2004GC000757), 2005 2. Fekiacova, Z. and Abouchami, W., Eos Trans. AGU, 84(46), Fall Meet. Suppl., Abstract V32A-0991, 2003. 3. Abouchami et al., Nature 434, 851-856, 2005 4. Galer, S.J.G. et al., Eos Trans. AGU, 80(46), Fall Meet. Suppl., Abstract V11E-08, 1999 5. Eisele et al., Geochem. Geophys. Geosyst., 4(2), doi:10.1029/2002GC000339, 2003 6. Ribe N.M. and Christensen U.R. Earth Planet. Sci. Letters 171, 517-531, 1999
DE: 3619 Magma genesis and partial melting (1037)
DE: 3621 Mantle processes (1038)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8415 Intra-plate processes (1033, 3615)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005