168 Prospectus

Site: HT-2A

Priority: 1
Position: 47°55.04´N; 128°47.52´W
Water Depth: 2608 m
Sediment Thickness: 195 m
Total Penetration: 195 mbsf (stop at first basement recovery)
Seismic Coverage: Line 95-15, SP 300 (Fig. 4, Appendix 1A)

Objectives: The Hydrothermal Transition site comprises a suite of four holes spanning a transition from open to sediment-sealed hydrothermal circulation. Holes are sited from 200 m to 20 km away from the nearest basement outcrop. Heat flow across the transect increases from about 15% to more than 80% of expected lithospheric values; upper basement temperatures increase from a few degrees to more than 40°C; hydrothermal fluid composition changes from normal to altered seawater; upper crustal seismic velocities increase from approximately 3.5 to more than 5.5 km/s. This hole is anticipated to find basement at roughly 15°C.

Drilling Program: APC/XCB

Logging and Downhole: APC temperature at up to every core; five temperature probe trips

Nature of Rock Anticipated: Turbidite sediments, weakly altered basalt

To Site HT-3A

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