HR: 1330h
AN: V22C-0593    [PDF]
TI: Eruptive style and geochemistry of North Arch lavas
AU: * Hirano, N
EM: nhirano@geo.titech.ac.jp
AF: Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Clague, D
EM: clague@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039-9644 United States
AU: Takahashi, E
EM: etakahas@geo.titech.ac.jp
AF: Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Hirata, T
EM: hrt1@geo.titech.ac.jp
AF: Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551 Japan
AU: Coombs, M
EM: mcoombs@usgs.gov
AF: U.S. Department of the Interior, U.S. Geological Survey, 345 Middlefield Rd Mail Stop 910, Menlo Park, CA 94025 United States
AU: Eakins, B
EM: beakins@usgs.gov
AF: U.S. Department of the Interior, U.S. Geological Survey, 345 Middlefield Rd Mail Stop 910, Menlo Park, CA 94025 United States
AB: Following JAMSTEC's initial bathymetric survey of the North Arch volcanic field in 1999 (Clague et al., 2002), we revisited the area with R/V Yokosuka in 2002 and have now mapped 90% of the lava field using SeaBeam 2112. Two types of volcanic cones are recognized; 1) flat top cones representing lava lakes formed above vents, and 2) steep sided cones made of highly vesiculated pillow lava and hyaloclastite. These volcanic cones are distributed mainly on the southern slope from the hinge line of the arch, perhaps reflecting the steeper slope south of the flexural arch. In the area where the volcanic cones are clustered, there is a subtle swell, which might be explained by a series of shallow level intrusive sheets (sills) near the vents. Two submersible dives were conducted in 2002. The first dive was in the central vent area and observed and sampled a flat top cone and an adjacent steep sided cone to clarify the volcanic sequence. The steep sided cone consisted of highly vesiculated pillow lava and breccia (hyaloclastite) of basanite composition. The lavas in the flat top cone and the sheet flow are dense alkali-olivine basalt. The steep sided cone appears to have erupted after the flat-topped cone was emplaced as the flat top cone is covered by pyroclastic ejecta (including submarine limu o Pele and Pele's tears) that most likely came from the steep sided cone. The second dive, on a sheet flow at the western edge of North Arch, explored the vent region for a long narrow flow. Uplifted and disrupted sediment observed during the dive suggest that intrusions were important in the development of the flow field. Trace element compositions of recovered samples, determined by LA-ICPMS have patterns generally similar to other ocean island basalts, except for significantly higher Ba and lower K, Zr, and Hf. The basanite lavas have distinctly higher concentrations of LILE, HFSE and LREE than the alkali basalts but are similar in HREE. These geochemical variations imply that the lavas formed from different degrees of partial melting of similar source in the stability field of garnet as proposed by Frey et al., (2000). Our preliminary conclusions are; 1) the eruption style of North Arch lavas is largely determined by volatile contents (Dixon et al., 1997); and 2) at the first dive site, voluminous effusive alkali-olivine basalt lavas formed flat top cones and sheet flows that were followed by submarine strombolian-type eruptions of basanite that formed steep sided cones. A more detailed geologic history of the North Arch volcanic field should be developed, but will require more dives and radiometric dating of lava flows.
DE: 3045 Seafloor morphology and bottom photography
DE: 3600 MINERALOGY AND PETROLOGY (replaces
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
DE: 8414 Eruption mechanisms
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting