HR: 0800h
AN: V41D-1497    [Abstracts]
TI: Geochemical Systematics of Hawaiian Post-shield Lavas: Implications for the Chemical Structure of the Hawaiian Mantle Plume
AU: * Hanano, D
EM: dhanano@eos.ubc.ca
AF: Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Weis, D
V41D-1497 AF: Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Aciego, S
V41D-1497 AF: Center for Isotope Geochemistry, Earth and Planetary Science, University of California, Berkeley, CA 94720-4767 United States
AU: Scoates, J S
V41D-1497 AF: Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: DePaolo, D J
V41D-1497 AF: Center for Isotope Geochemistry, Earth and Planetary Science, University of California, Berkeley, CA 94720-4767 United States
AB: High-precision Pb and Hf isotopic ratios by MC-ICP-MS and trace element concentrations by HR-ICP-MS of lavas forming Hawaiian volcanoes allow for new perspectives in the study of the source components associated with the Hawaiian mantle plume. In particular, late-stage lavas represent small-volume eruptions and small degrees of melting, and can provide better resolution of the geochemical heterogeneities in the plume. This study involves post-shield lavas from the Mauna Kea, Kohala, and Hualalai volcanoes on the island of Hawaii. Lavas from these specific volcanoes provide information about the region in which the plume is being deflected and sheared to the northwest by the movement of the Pacific plate. Pb isotopic compositions from Hualalai are the least radiogenic with ²⁰⁶Pb/²⁰⁴Pb = 17.888-18.028, compared to 18.343-18.408 for Mauna Kea and 18.286-18.439 for Kohala, which is consistent with each volcano belonging to their respective Loa-Kea Pb trends. Mauna Kea post-shield lavas are less radiogenic in Pb than the shield and post-shield Mauna Kea lavas from HSDP-2, showing a systematic decrease as the volcano evolved from the shield to post-shield stage. A similar trend is observed between the tholeiites and alkaline lavas of Hualalai, while the opposite trend is observed for Kohala. Hualalai and Kohala post-shield lavas form linear arrays in Pb-Pb space with their respective tholeiites, indicating an origin from the same source. However, the relative proportions of the components involved in the genesis of the post-shield lavas appear to be different. Mauna Kea post-shield lavas lie along the lower extension of the Kea-lo8 array of HSDP-2 (Eisele et al., 2003), distinct from older (350-550 kyr) Mauna Kea lavas and recent Kilauea lavas (Abouchami et al., 2005). The low ²⁰⁶Pb/²⁰⁴Pb ratios of Hualalai post-shield lavas are indicative of a unique component in that volcano. The Pb isotopic compositions of the post-shield lavas are thus sampling isotopically distinct compositional streaks at more peripheral parts of the Hawaiian plume that are not seen in the main tholeiitic stage.
DE: 1000 GEOCHEMISTRY
DE: 1025 Composition of the mantle
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005