Site summaries (continued)

Proposed Site LOUI-9A (Seamount 168.3°W - Koko equivalent)

Priority: Alternate site
Position: 37°59.72′S, 168°17.11′W
Water depth (m): 1150
Target drilling depth (mbsf): ~465 (115 m sediment; ≥350 m basement)
Approved maximum penetration (mbsf): 465 (350 m basement; additional basement penetration must be reviewed by the operator during drilling operations)
Survey coverage: • AMAT02RR (Fig. AF21)
• Line AMAT 168.3-1 (CDP 24118) (Fig. AF22)
• Line AMAT 168.3-2 (CDP 25393) (Fig. AF23)
Objective: (see text for details) 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.
Drilling, coring, and downhole measurement program: • RCB coring to TD.
• FFF deployment and two bit changes (two reentries).
• Wireline logging (triple combo, FMS-sonic, and magnetometer).
Anticipated lithology (mbsf): • 0–10: pelagic ooze
• 10–115: lithified limestones, volcaniclastics, and minor lava flows(?)
• >115: basalt (~48 m.y. old)
Site characterization: This alternate site is very close to and only 0.3° northeast of proposed primary Site LOUI-4B on the 168.6°W guyot. Three new 40Ar/39Ar ages (48.2 ± 0.3, 47.4 ± 0.5, and 50.4 ± 0.5 Ma) have been measured, and these are similar to the 49 Ma age of Koko Seamount in the Emperor Seamount Trail. The estimated pelagic cap is ~8–10 m thick over large summit areas based on 3.5 kHz CHIRP data (0.010 s two-way traveltime at 1.6–1.9 km/s). The intercalated sequence of volcaniclastics and lava flows is estimated to be at least 75–105 m thick (0.060 s two-way traveltime at 2.5–3.5 km/s), although the sequence at this site is less developed in the multichannel seismic reflection data.