HR: 0800h
AN: V51B-0549    [Abstracts]
TI: The Chemical Structure of the Hawaiian Mantle Plume
AU: * Ren, Z
EM: ren@geo.titech.ac.jp
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo, 152-8551 Japan
AU: Hirano, N
EM: nhirano@geo.titech.ac.jp
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo, 152-8551 Japan
AU: Hirata, T
EM: hrt1@geo.titech.ac.jp
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo, 152-8551 Japan
AU: Takahashi, E
EM: etakahas@geo.titech.ac.jp
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo, 152-8551 Japan
AU: Ingle, S
EM: single@geo.titech.ac.jp
AF: Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguroku, Tokyo, 152-8551 Japan
AB: Numerous geochemical studies of Hawaiian basaltic lavas have shown that the Hawaiian mantle plume is isotopically heterogeneous. However, the distribution and scale of these heterogeneities remain unknown. This is essentially due to the complex interactions created by melting a heterogeneous source, subsequent aggregation of the melts on their way to the surface, and mixing that takes place in shallow magma chambers prior to eruption. In sum, the measured compositions of bulk lavas may represent only _eaverage_f compositions that do not fully reflect the complexity of either the mantle source heterogeneity and/or chemical structure. Melt inclusions, or samples of the local magma frozen in olivine phenocrysts during their formation, are better at recording the complex magmatic history than are the bulk samples. Here, we report major and trace element compositions of olivine-hosted melt inclusions from submarine Haleakala lavas that were collected by 2001-2002 JAMSTEC cruises measured by EPMA and LA-ICP-MS after homogenization at $1250\deg$C, QFM for 20min. Melt inclusions from the submarine Hana Ridge (Haleakala volcano) show large ranges in CaO/Al$_{2}$O$_{3}$ (0.92-1.50), TiO$_{2}$/Na$_{2}$O (0.79-1.60) and Sr/Nb (14.56-36.60), Zr/Nb (6.48-16.95), ranging from Kilauea-like to Mauna Loa-like compositions within separately-sampled lavas as well as in a single host lava sample. Bulk rocks geochemistry shows that major element composition and trace element ratios such as Zr/Nb, Sr/Nb (Ren et al., 2004a, in press, J. Petrol.) together with Pb, Nd and Sr isotopic ratios (Ren et al., 2004b, submitted to J. Petrol.) of Haleakala shield volcano also display systematic compositional variation changing from a Kilauea-like in the submarine Hana Ridge (main shield stage) to Kilauea-Mauna Loa-like in the subaerial Honomanu stage (late shield stage, data from Chen and Frey, 1991). Some of the compositional variations in melt inclusions in single rocks are wider range than over-all variation observed in bulk rocks. It is important that both Kilauea-like and Mauna Loa-like compositions co-exist in melt inclusions in single submarine Hana Ridge rocks which are identified as Kilauea-like based on bulk geochemistry. These observations are inconsistent with the current interpretation that magma compositions are controlled by concentric zonation of the Hawaiian mantle plume (e.g. Kea component and Loa component), manifested as the Kea trend and the Loa trend volcanoes (e.g. Hauri, 1996; Lassiter et al., 1996). Our new data from olivine-hosted melt inclusions imply that the chemical structure of the Hawaiian mantle plume is significantly more complicated than previously modeled and the length-scale of chemical heterogeneity must be remarkably smaller than estimated based on bulk rock geochemistry.
DE: 8400 VOLCANOLOGY
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting