HR: 0800h
AN: V51B-0546    [Abstracts]
TI: High precision Pb, Sr, and Nd isotope geochemistry of alkalic early Kilauea magmas from the submarine Hilina bench region, and the nature of the Hilina/Kea mantle component
AU: * Kimura, J
EM: jkimura@riko.shimane-u.ac.jp
AF: Shimane University, Nishikawatsu 1060, Matsue, 690-8504 Japan
AU: Sisson, T W
EM: tsisson@usgs.gov
AF: US Geological Survey, Middlefield Road, Menlo Park, CA 94025 United States
AU: Nakano, N
EM: s029207@matsu.shimane-u.ac.jp
AF: Shimane University, Nishikawatsu 1060, Matsue, 690-8504 Japan
AU: Coombs, M L
EM: mcoombs@usgs.gov
AF: US Geological Survey, Middlefield Road, Menlo Park, CA 94025 United States
AU: Lipman, P W
EM: plipman@usgs.gov
AF: US Geological Survey, Middlefield Road, Menlo Park, CA 94025 United States
AB: Submarine lavas recovered from the Hilina bench region, offshore Kilauea, Hawaii Island provide information on ancient Kilauea volcano and the geochemical components of the Hawaiian hotspot. Alkalic lavas, including nephelinite, basanite, hawaiite, and alkali basalt, dominate the earliest stage of Kilauea magmatism. Transitional basalt pillow lavas are an intermediate phase, preceding development of the voluminous tholeiitic subaerial shield and submarine Puna Ridge. Most alkalic through transitional lavas are quite uniform in Sr-Nd-Pb isotopes, supporting the interpretation that variable extent partial melting of a relatively homogeneous source was responsible for much of the geochemical diversity of early Kilauea magmas (Sisson et al., 2002). These samples are among the highest 206Pb/204Pb known from the Hawaii islands and may represent melts from a distinct geochemical and isotopic endmember involved in the generation of most Hawaiian tholeiites. This endmember is similar to the postulated literature Kea component, but we propose it should be renamed Hilina, to avoid confusion with the geographically defined Kea-trend volcanoes. Isotopic compositions of some shield-stage Kilauea tholeiites overlap the Hilina endmember but most deviate far into the interior of the isotopic field defined by magmas from other Hawaiian volcanoes, reflecting the introduction of melt contributions from both _gKoolau_h (high 87Sr/86Sr, low 206Pb/204Pb) and depleted (low 87Sr/86Sr, intermediate 206Pb/204Pb) source materials. This shift in isotopic character from nearly uniform, endmember, and alkalic, to diverse and tholeiitic corresponds with the major increase in Kilauea_fs magmatic productivity. Two popular geodynamic models can account for these relations: (1) The upwelling mantle source could be concentrically zoned in both chemical/isotopic composition, and in speed/extent of upwelling, with Hilina (and Loihi) components situated in the weakly ascending margins and the Koolau component in the interior. The depleted component could be refractory and spread throughout or scavenged from the overlying lithosphere. (2) The Hilina (and Loihi) components could be more fertile material (lower melting temperature) spread irregularly throughout the Hawaiian source in a matrix of more refractory depleted and Koolau compositions. Modest upwelling along the leading hotspot margin melts the fertile domains predominantly, while the refractory matrix also partially melts in the more vigorously upwelling hotspot interior, diluting the Hilina and Loihi components and yielding voluminous isotopically diverse tholeiitic magmas.
DE: 1749 Volcanology, geochemistry, and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting