Koko Guyot

Coordinates: 35°15′N 171°35′E / 35.250°N 171.583°E / 35.250; 171.583
Source: Wikipedia, the free encyclopedia.
Koko Guyot
Hawaiian-Emperor seamount chain
Age of rock48.1 million[3]
Last eruption40 million years ago[4]
History
First visit1973, ODP Site 308

Koko Guyot is a 48.1-million-year-old

Hawaiian-Emperor seamount chain.[5] Pillow lava has been sampled on the north west flank of Koko Seamount, and the oldest dated lava is 40 million years old.[4] Seismic studies indicate that it is built on a 9 km (6 mi) thick portion of the Pacific Plate.[6] The oldest rock from the north side of Koko Seamount is dated at 52.6 and the south side of Koko at 50.4 million years ago. To the southeast of the bend is Kimmei Seamount at 47.9 million years ago and southeast of it, Daikakuji at 46.7.[7]

Geology and characteristics

The seamount was named for the 58th emperor of Japan,

Emperor Koko (A.D. 885-887) by geologist Thomas Davies and his colleagues in 1972, based on the results from a bathymetric expedition and contents of two dredge hauls, led by Thomas Washington and undertaken with the ship Aries-7.[2][5] The seamount is elongate in shape, aligned northwest-southeast (the same direction as the chain), and has a gentle slope and a large, flat top. Koko Seamount also has a lot of small reefal bodies on its slopes.[2] It rises from the abyssal floor
about 5,000 m (16,000 ft) in height.

A prominent south-trending ridge extends about 50 km (31 mi) from the summit area in the direction of

Ojin Seamount about 200 km (124 mi) to the northwest and Kimmei Seamount 100 km (62 mi) to the southeast.[5] The seamount is located just 2.3 degrees north of the bend.[2]

Much of what we know about Koko comes from early dredgings and the Ocean Drilling Program's core samples, collected as part of Leg 197, at Site 1206, which aimed to supply information on the relatively obscure Emperor seamounts and study their relation to the Hawaiian chain.[2][8] Site 1206 was the last and southernmost drilling site during Leg 197, and was located on the southeastern side of the lower summit terrace of Koko Seamount.[2] A seismic survey of the region was utilized to locate a suitable place for the drill site, initially targeted near Site 308, drilled in 1973 during Leg 32. Weather conditions during the drilling had prevented it from reaching 68.5 m (225 ft) in depth, the approximate depth of the sediment cover in the region.[2] Due to a shortage of time, priority was placed on finding a region with a thin sedimentary cover. The site eventually chosen was located at a water depth of 1,545 m (5,069 ft), 6.2 km (4 mi) south of Site 308, at coordinates 34°55.55′N 172°8.75′E / 34.92583°N 172.14583°E / 34.92583; 172.14583. The sediment cover at this site was less than half that at the 1973 drill site, and rock was hit at a subsurface depth of 57 m (187 ft). Drilling continued to 278 m (912 ft) into the slopes.[2]

The top 57 m (187 ft) of sediment included fossil-rich calcarenite and calcium-rich mudstone and siltstone, indicating a shallow-water setting at the time of deposition.[2] The lower part of the core sample recovered a 15 cm (6 in) to 20 cm (8 in) section of shell-bearing mudstone containing many microfossils typical of the early to middle Eocene (43.5-49.7 Ma). This age range fits well with a radiometric analysis (48.1 Ma) reported for a dredged rock from Koko Seamount from the 1973 expedition. Although shell fragments had been recovered from the sediment cover in 1973, none of these deposits contained microfossils.[2]

Lava flows dominate the

phyric lava, and tholeiitic or alkalic in composition. The basaltic lavas from Koko Seamount resemble those drilled during Leg 55, at Suiko Seamount.[2]

Studies suggested that the magnetic arrangement of the rock, used to determine its latitude at formation (magnets align to the

percent of error is +8.4°/-10.9°). That would put the seamount at 21.7° N in latitude during its early history, before the Pacific Plate moved it to its current position relative to Earth.[2]

Ancient ecology

Dredged carbonate samples from the top of the seamount contained

bryozoans, and coralline at deeper depths. The recorded lepidocyclinids indicate an Early Miocene age for the drowned carbonate platforms found on the seamount, at about 500 m (1,640 ft).[9]

See also

See also

  • List of volcanoes in the Hawaiian – Emperor seamount chain

References

  1. ^ "Seamount Catalog". Seamounts database. EarthRef, a National Science Foundation project. Retrieved 2009-04-09.
  2. ^ a b c d e f g h i j k l m "SITE 1206". Ocean Drilling Program Database-Results of Site 1206. Ocean Drilling Program. Retrieved 2009-04-09.
  3. ^ a b Dyar, Darby. "HOTSPOTS AND PLATE MOTION". Archived from the original on 2011-06-07. Retrieved 2009-04-04.
  4. ^ a b Seach, John. "Koko Seamount, NW Flank - John Seach". Volcanic database. Volcano Live.com. Retrieved 2009-04-09.
  5. ^ a b c d e "6. Site 12061 BACKGROUND AND SCIENTIFIC OBJECTIVES". Drilling Site Recommendation Submission for Koko. Ocean Drilling Program. Retrieved 2009-04-09.
  6. ^ K. FURUKAWA; J. F. GETTRUST; L. W. KROENKE; J. F. Campbell (1980). "Crust and upper mantle structure along the flank of Koko Seamount". Scientific Paper-Abstract. Hawaii Institute of Geophysics University of Hawaii, Honolulu, Hawaii 96822. Retrieved 2009-04-09.
  7. ^ TenBruggencate, Jan (2006). "Hawaiian geology gets update". Honolulu Advertiser web article. Honolulu Advertiser. Retrieved 2009-04-09.
  8. ^ "DRILLING STRATEGY". Ocean Drilling Program - Leg 197 Proposal. Ocean Drilling Program. Retrieved 2009-04-09.
  9. ^ David A. Clauge; Juan C. Braga; Jody M. Webster; Davide Bassi; Willen Renema. "Lower Miocene submerged reefs on the Koko Seamount". Essay Abstract. Retrieved 2009-04-09.
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