Objectives: (1) Provide estimates of the sediment inputs and altered basalt inputs (geochemical fluxes) into the Izu-Bonin subduction zone. (2) Contrast crustal budgets here with those for the Marianas to test whether along-strike differences in the volcanics can be explained by along-strike variations in the crustal inputs. (3) Compare basement alteration characteristics with those at Hole 801C (also in old Pacific crust). (4) Provide constaints on the Early Cretaceous paleomagnetic time scale. (5) Provide constraints on mid-Cretaceous CCD and equatorial circulation fluctuations.
Drilling Program: APC, XCB, MDCB, RCB
Logging and Downhole Operations: Triple combo, GLT, FMS/Sonic, GHMT, ARI, Permeability
Nature of Rock Anticipated: Pelagic clay with volcanic arc ash (150 m); cherty porcellanites and
chalks (450 m); basaltic pillows, flows, breccia, and possibly dikes (>300 m)
SITE: BON-9 (alternate to 8A)
PRIORITY: 2
POSITION: 31°18.5´N, 143°2.5´E
WATER DEPTH: 5875 m
SEDIMENT THICKNESS: 600 m
TOTAL PENETRATION: 900 m
SEISMIC COVERAGE:
Objectives: Same objectives as BON-8A.
SITE: 801C
PRIORITY: 1
POSITION: 18.642°N, 156.36°E
WATER DEPTH: 5674 m
SEDIMENT THICKNESS: 460 m
TOTAL PENETRATION: 950 m
SEISMIC COVERAGE: MESOPAC II, Line 10 at 0600, 8/26/89
Objectives: (1) Characterize the geochemical fluxes and geophysical aging attending the upper oxidative alteration of the oceanic crust at Hole 801C. (2) Compare igneous compositions, structure, and alteration with other drilled sections of in situ oceanic crust (in particular Hole 504B, contrasting a young site in Pacific crust with the oldest site in Pacific crust). (3) Help constrain models for seafloor alteration that depend on spreading rate and age (Hole 801C is the world's oldest oceanic crust and was formed at a fast-spreading ridge, so it embodies several end-member characteristics). (4) Test models for the Jurassic Magnetic "Quiet" Zone.
Drilling Program: RCB
Logging and Downhole Operations: Triple Combo, GLT, FMS/Sonic, ARI, Permeability
Nature of Rock Anticipated: Basaltic pillows, flows, breccia, and possibly dikes (>350 m)
SITE: PIG-3B (alternate to 801C)
PRIORITY: 2
POSITION: 18.663°N, 157.095°E
WATER DEPTH: 5674 m
SEDIMENT THICKNESS: 460 m
TOTAL PENETRATION: 950 m
SEISMIC COVERAGE:
Objectives: Same objectives as Hole 801C.