Table T4. 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 inch 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, piece, interval (cm) | Top igneous unit | Depth (mbsf) | Criteria |
|---|---|---|---|---|---|
| Lavas | Lava pond | 206-1256D-2R-1 (Piece 1, 0) | 1256D-1(1256C-1 through 18) | ~250 | Massive ponded lava including overlying sheet flows. |
| Inflated flows | 206-1256D-13R-1 (Piece 1, 0) | 1256D-2 | 350.3 | Massive sheet and pillowed flows with rare inflation features. | |
| Sheet and massive flows | 206-1256D-43R-1 (Piece 1, 0) | 1256D-16 | 533.9 | Sheet flows with subordinate massive flows. | |
| Transition zone | 309-1256D-117R-1 (Piece 6, 85) | 1256D-40 | 1004.1 | Sheet flows with breccias, rare dikes, and alteration at (sub-) greenschist facies conditions. | |
| Sheeted dike complex | Upper dikes | 309-1256D-129R-1 (Piece 1, 0) | 1256D-44a | 1060.9 | Massive basalts, common subvertical intrusive contacts. Elevated VP and TC. |
| Granoblastic dikes | 312-1256D-192R-1 (Piece 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 | 1406.6 | Medium-grained gabbroic rocks intrude overlying dikes: gabbro, disseminated oxide gabbro, patchy gabbro, and quartz-rich oxide diorite. |
| 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, magnetite, ilmenite, 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 1256D-95 at 1502.6 mbsf. |
Note: TC = thermal conductivity.
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