Scientific Participants |
Table of Contents
Site: OSN-2
Priority: 1
Position: 5°17.566'N, 110°04.579'W
Water Depth: 3860 m
Sediment Thickness: 116 m
Target Drilling Depth: 216 mbsf
Approved Maximum Penetration: Unlimited (pending approval)
Seismic Coverage: North-south SCS line collected during ODP Leg 138. North-south analog seismic line collected during the Thomas Washington Venture 1 cruise. Proposed observatory site is at ODP Site 852 cored during Leg 138.
Objectives: The objectives at proposed Site OSN-2 are to:
- Drill a reentry hole into basement for a permanent broadband borehole seismograph;
- Provide a borehole for other long-term borehole measurements; and
- Provide a "reference site" with in situ igneous samples in normal, fast-spreading, ~12-Ma ocean crust to constrain geochemical and hydrothermal models of crustal evolution.
Drilling Program: Jet-in a reentry cone with 20-in casing to 40-60 mbsf; drill to 140 mbsf, install 16-in casing to 130 mbsf, which is ~14 m into basement; RCB core from 140 to 216 mbsf or deeper if time permits, log with the triple-combo and FMS/sonic tool strings, open hole and set 10.75-in casing ~5 m above the total depth of the hole. If time permits, drill a second hole to ~80-90 mbsf, RCB core to ~140 mbsf, and log with the triple-combo and FMS/sonic tool strings.
Logging and Downhole: Triple-combo and FMS/sonic.
Nature of Rock Anticipated: Soft sediment and fractured pillow basalt. See Figure F5 and Figure F7 for the seismic lines and Figure F4 and Figure F6 for the track lines.
Scientific Participants |
Table of Contents