HR: 0800h
AN: V51B-0547    [Abstracts]
TI: Submarine Alkalic Lavas Around the Hawaiian Hotspot; Plume and Non-Plume Signatures Determined by Noble Gases
AU: * Hanyu, T
EM: hanyut@jamstec.go.jp
AF: Institute for Frontier Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho 2-15, Yokosuka, 237-0061 Japan
AU: Clague, D A
EM: clague@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039 United States
AU: Kaneoka, I
EM: Ikaneoka@aol.com
AF: Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo, 113-0032 Japan
AU: Dunai, T J
EM: dunt@geo.vu.nl
AF: Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, 1081HV Netherlands
AU: Davies, G R
EM: gareth.davies@falw.vu.nl
AF: Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, Amsterdam, 1081HV Netherlands
AB: Noble gas isotopic ratios were determined for submarine alkalic volcanic rocks distributed around the Hawaiian islands to constrain the origin of such alkalic volcanism. Samples were collected by dredging or using submersibles from the Kauai Channel between Oahu and Kauai, north of Molokai, northwest of Niihau, Southwest Oahu, South Arch and North Arch volcanic fields. Sites located downstream from the center of the hotspot have 3He/4He ratios close to MORB at about 8 Ra, demonstrating that the magmas erupted at these sites had minimum contribution of volatiles from a mantle plume. In contrast, the South Arch, located upstream of the hotspot on the Hawaiian Arch, has 3He/4He ratios between 17 and 21 Ra, indicating a strong plume influence. Differences in noble gas isotopic characteristics between alkalic volcanism downstream and upstream of the hotspot imply that upstream volcanism contains incipient melts from an upwelling mantle plume, having primitive 3He/4He. In combination with lithophile element isotopic data, we conclude that the most likely source of the upstream magmatism is depleted asthenospheric mantle that has been metasomatised by incipient melt from a mantle plume. After major melt extraction from the mantle plume during production of magmas for the shield stage, the plume material is highly depleted in noble gases and moderately depleted in lithophile elements. Partial melting of the depleted mantle impregnated by melts derived from this volatile depleted plume source may explain the isotopic characteristics of the downstream alkalic magmatism.
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1010 Chemical evolution
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting