168 Prospectus

Proposed Drill Sites

Site: HT-1A

Priority: 1
Position: 47°55.56´N; 128°50.02´W
Water Depth: 2600 m
Sediment Thickness: 85 m
Total Penetration: 85 mbsf (stop at first basement recovery)
Seismic Coverage: Line 95-15, S.P. 170 (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 in the oceanic crust. Holes are sited from 200 m to about 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 located in the youngest crust of the transect, and only a few hundred meters from outcropping basement. Basement temperature is expected to be less than 10°C.

Drilling Program: APC/XCB (if necessary)

Logging and Downhole: APC temperature every core

Nature of Rock Anticipated: Turbidite sediments, unaltered basalt

To Site HT-2A

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