SITE SUMMARY

Site: 439 (DSDP Leg 57)

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To 186 Site 439 Line JNOC-1

Priority: 2
Position: 40°37.61´N, 143°18.63´E
Water Depth: 1666 m
Sediment Thickness: 1140 m above Cretaceous basement
Target Drilling Depth: 1000-1200 m
Approved Maximum Penetration: PPSP approval needed
Seismic Coverage:

Objectives: This is a back-up site for JT-2G. The objectives of Site 439 are:

1. Install long-term geophysical borehole observatory to monitor strain, seismicity, tilt, and temperature. Quantify episodic plate motions within seismically inactive part of the interplate seismogenic zone.
2. Constrain subsidence history of the Japan Trench forearc.
3. Determine nature of Cretaceous basement, if time permits.

Drilling Program: APC to 250 mbsf, XCB to 450 mbsf, and RCB to 1000 mbsf. Coring will be done only if time permits because this site was previously cored on Leg 57. Drill the instrumented borehole to ~1000 mbsf, install reentry cone, and case through unstable section.

Logging and Downhole Operations: Triple combo, FMS/sonic/temperature, BHTV; install long-term sensor package and cement at the bottom.

Nature of Rock Anticipated: Sandy, silty, pebbly clay with ash layers (50 m); clayey diatom ooze, diatomaceous clay, ash layers (~300 m); diatomaceous claystone, clayey diatomite (~250 m); claystone, diatomaceous claystone, calcareous claystone (~200 m); sandy claystone, diatomaceous claystone (~125 m); turbidites and silty claystone (~75 m), sandstone and siltstone (~100 m), boulder to pebble conglomerate and breccia, dacite and mudstone clasts (~50 m); and silicified claystone (~100 m).

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