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Earth Planets Space, Vol. 61 (No. 3), pp. 319-331, 2009
Tae-Gook Lee1, Kiehwa Lee2, James R. Hein3, and Jai-Woon Moon4
1Development Operations Team, Korea National Oil Corporation, 1588-14, Anyang 431-711, Korea
2School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea
3U.S. Geological Survey, 345 Middlefield Rd., MS 999, Menlo Park, CA, 94025-3591, USA
4Marine Resources Research Department, Korea Ocean Research and Development Institute, Ansan
P.O. Box 29 425-600, Korea
(Received October 13, 2004; Revised October 9, 2008; Accepted October 21, 2008; Online published March 3, 2009)
Abstract:
This paper provides an analysis of multi-channel seismic data obtained during 2000-2001 on seamounts near the Ogasawara Fracture Zone (OFZ) northwest of the Marshall Islands in the western Pacific. The OFZ is unique in that it is a wide rift zone that includes many seamounts. Seven units are delineated on the basis of acoustic characteristics and depth: three units (I, II, and III) on the summit of seamounts and four units (IV, V, VI, and VII) in basins. Acoustic characteristics of layers on the summit of guyots and dredged samples indicate that the seamounts had been built above sea level by volcanism. This was followed by reef growth along the summit margin, which enabled deposition of shallow-water carbonates on the summit, and finally by subsidence of the edifices. The subsidence depth of the seamounts, estimated from the lower boundary of unit II, ranges between 1,550 and 2,040 m. The thick unit I of the southern seamounts is correlated with proximity to the equatorial high productivity zone, whereas local currents may have strongly affected the distribution of unit I on northern seamounts. A seismic profile in the basin around the Ita Mai Tai and OSM4 seamounts shows an unconformity between units IV and V, which is widespread from the East Mariana Basin to the Pigafetta Basin.
Key words:
Ogasawara Fracture Zone, acoustic characteristics, subsidence depth, unconformity.