HR: 0800h
AN: V41C-1468    [Abstracts]
TI: Hf, Pb, Sr, and Nd Isotope Geochemistry of Submarine Lavas from Hualalai Volcano, Hawaii
AU: * Yamasaki, S
EM: 041d8532@sci.stud.kumamoto-u.ac.jp
AF: Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AU: Kani, T
EM: kani@sci.kumamoto-u.ac.jp
AF: Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AU: Hanan, B B
EM: barry.hanan@ geology.sdsu.edu
AF: San Diego State University, 5500 Campanile Dr, San Diego, CA 92182-1020 United States
AU: Nohda, S
EM: snohda@sci.kumamoto-u.ac.jp
AF: Kumamoto University, 2-39-1 Kurokami, Kumamoto, 860-8555 Japan
AB: The volcanoes of the Hawaiian islands are distributed in two parallel trends ('Loa' and 'Kea'), whose rocks are characterized by general geochemical differences. It is broadly accepted that Hawaiian plume is composed of several components, but the chemical structure of Hawaiian plume remains a matter of considerable debate. Hualalai volcano, the third youngest on the island of Hawaii and located on Loa trend, has been in the post shield alkalic stage for >100 ky. The study of the deep submarine ridges of this volcano has not been previously conducted. Many of submarine ridge lavas are older than any exposed on land, and extend our view of Hualalai magmatism back in time. To identify source materials involved in Hualalai ridge volcanism can provide constraints on the chemical structure of the Hawaiian plume. We analyzed Hf, Pb, Sr, Nd isotopic compositions and trace element contents of 16 lava samples from the submarine ridges of Hualalai. The samples were collected from North Kona region at 2700 - 3500 m water depth by 2001 Kaiko dive (K219) and at 2100 - 4500 m depth by 2002 Shinkai 6500 dives (S690, S692). It is considered that these samples are older than 105 ka, and are erupted at the pre-shield or shield stage of this volcano based on the stratigraphy and lithology. Isotopic compositions of the lavas have ⁸⁷ Sr/⁸⁶Sr ratios ranging from 0.703638 to 0.703813, ¹⁴³Nd/¹⁴⁴Nd from 0.512932 to 0.512946, ¹⁷⁶Hf/¹⁷⁷Hf from 0.2830988 to 0.2831234, ²⁰⁶Pb/²⁰⁴Pb from 18.1554 to 18.2663, ²⁰⁷Pb/²⁰⁴Pb from 15.4488 to 15.5518, and ²⁰⁸Pb/²⁰⁴Pb from 37.8661 to 38.2583. Hf, Nd, Sr isotopic compositions of the basalt samples are similar to, and overlap with the data previously reported for shield stage tholeiite from Hualalai and older tholeiite (>100ka) from Mauna Loa. Some of new Pb isotopic data have higher ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb, for a given ²⁰⁶Pb/²⁰⁴Pb, than published data from Mauna Loa and Hualalai. The results indicate that the Loa Pb isotope signature of the Hualalai source was present before 105 ka.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005