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doi:10.2204/iodp.pr.312.2006

Table T2. Key parameters for Hole 1256D and preliminary subdivisions of the upper oceanic crust at Site 1256 adopted for Expeditions 309 and 312.

Location: 6°44.163'N, 91°56.061'W
Water depth (m): 3634.7
Sediment thickness (m): 250
16-in casing string (m): 269.5
Interval in Hole 1256D drilled during
ODP Leg 206: 752 mbsf, 502 msb
IODP Expedition 309: 1255.1 mbsf, 1005.1 msb
IODP Expedition 312: 1507.1 mbsf, 1257.1 msb

Major lithologic zone
Sublithology
Top core, section,
interval (cm)
Top igneous unit
Depth (mbsf)
Criteria






Lavas
Lava Pond
206-1256D-2R-1, 0
1256D-1
(1256C-1 through 18)
~250
Massive ponded lava including overlying sheet flows.
Inflated Flows
206-1256D-13R-1, 0
1256D-2
350.3
Massive sheet and pillowed flows with rare inflation features.
Sheet and massive flows
206-1256D-43R-1, 0
1256D-16
533.9
Sheet flows with subordinate massive flows.
Transition zone

309-1256D-117R-1, 85
1256D-40
1004.2
Sheet flows with breccias, rare dikes, and alteration at (sub-) greenschist facies conditions.
Sheeted dike complex
Upper dikes
309-1256D-129R-1, 0
1256D-44a
1060.9
Massive basalts, common subvertical intrusive contacts. Elevated VP and TC.
Granoblastic dikes
312-1256D-192R-1, 0
1256D-78
1348.3
Granoblastic texture; equant grains; secondary clinopyroxene, orthopyroxene, plagioclase, hornblende, magnetite, and illite.
Plutonic section
Gabbro 1
312-1256D-213R-1 (Piece 13, 52)
1256D-81
1406.62
Medium-grained gabbroic rocks intrude overlying dikes: gabbro, disseminated oxide gabbro, patchy gabbro, and quartz-rich oxide diorite.
Upper dike screen
312-1256D-225R-1 (Piece 1, 0)
1256D-90
1458.9
Fine-grained to cryptocrystalline basalt dike. Highly altered, granoblastic texture, secondary clinopyroxene, orthopyroxene, plagioclase, mt, illite, and hornblende.
Gabbro 2
312-1256D-230R-1 (Piece 5, 15)
1256D-91
1483.1
Plutonic rock intrudes upper and lower dike screens; medium-grained gabbro, oxide-bearing quartz gabbro, oxide gabbro, orthopyroxene-bearing gabbro, trondjhemite; leucocratic-gabbro; all highly altered; stoped basalt.
Gabbronorite of uncertain origin.
Late dike Unit 95 at 1502.6 mbsf.

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