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Priority:
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Alternate site
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Position:
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32°13.44′S, 171°53.87′W
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Water depth (m):
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1560
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Target drilling depth (mbsf):
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~470 (120 m sediment; ≥350 m basement)
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Approved maximum penetration (mbsf):
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Approval pending (470 m requested)
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Survey coverage:
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• AMAT02RR (Fig. AF16)
• Line AMAT 32.33-2 (CDP 36889) (Fig. AF18)
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Objective: (see text for details)
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1. Core thin sediment cover and igneous basement until enough igneous units suitable to acquire accurate paleolatitudes and 40Ar/39Ar ages are recovered.
2. Study the geochemical evolution of this guyot. |
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Drilling, coring, and downhole measurement program:
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• RCB coring to TD.
• FFF deployment and two bit changes (two reentries).
• Wireline logging (triple combo, FMS-sonic, and magnetometer).
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Anticipated lithology (mbsf):
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• 0–10: pelagic ooze
• 10–120: lithified limestones, volcaniclastics, and minor lava flows(?)
• >120: basalt (~64 m.y. old)
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Site characterization:
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This alternate drilling site is located on another small guyot ~1.4° north of proposed primary Site LOUI-2B on the 33.7°S guyot, which gives this site an interpolated age of ~64–65 Ma, older than the Suiko Seamount (61 Ma) in the Emperor Seamount Trail. Three other seamounts also have crossing seismic lines; however, the 32.3°S seamount has the thinnest sequence of volcaniclastics. The estimated pelagic cap is ~10 m thick, with an intercalated sequence of volcaniclastics and lava flows estimated to be at least 70–110 m thick (0.055–0.060 s two-way traveltime at 2.5–3.5 km/s in volcaniclastic sediment). This guyot has a reflective summit (possibly due to a manganese pavement) and some small-scale roughness (5–20 m high peaks) that may be posterosional in origin or an erosional remnant (close-spaced small guyots like these can be submerged quickly before planation is complete, particularly if they end up in the flexural moat of the next-youngest volcano to load the lithosphere). This alternate site is preferred to alternate Site LOUI-7A because it is located farther away from the posterosional peaks or erosional remnants to the northeast.
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