Table T5. Key parameters for Hole 1256D and preliminary subdivisions of the upper oceanic crust at Site 1256 adopted for Expedition 335.
| Location: 6°44.163’N, 91°56.061’W | |||||
| Water depth (m): 3634.7; 3645.4 mbrf | |||||
| Sediment thickness (m): 250 | |||||
| Interval in Hole 1256C drilled during Leg 206: 338.5 mbsf, 88.5 msb | |||||
| Casing in Hole 1256D: | |||||
| Height of reentry cone: 2.4 m | |||||
| Internal diameter of reentry cone: 3.5 m (11 ft, 5 inches) | |||||
| 20 inch casing string (m): 95.12 | |||||
| 16 inch casing string (m) 269 | |||||
| Interval in Hole 1256D drilled during | |||||
| Leg 206: 752 mbsf, 502 msb; basement advance (m): 502 | |||||
| Expedition 309: 1255.1 mbsf, 1005.1 msb; basement advance (m): 503 | |||||
| Expedition 312: 1507.1 mbsf, 1257.1 msb; basement advance (m): 252 | |||||
| Expedition 335: 1521.6 mbsf, 1271.6 msb; basement advance (m): 14.5 | |||||
|
Major
lithologic zone
|
Sublithology
|
Top of lithology
|
Top igneous unit
|
Depth
(mbsf)
|
Criteria
|
|---|---|---|---|---|---|
| Lavas | Lava pond | 206-1256D-2R-1, 0 cm | 1256D-1 (1256C-1 through 1256C-18) | ~250 | Massive ponded lava including overlying sheet flows. |
| Inflated flows | 206-1256D-13R-1, 0 cm | 1256D-2 | 350.3 | Massive, sheet, and pillowed flows with rare inflation features. | |
| Sheet and massive flows | 206-1256D-43R-1, 0 cm | 1256D-16 | 533.9 | Sheet flows with subordinate massive flows. | |
| Transition zone | 309-1256D-117R-1, 85 cm | 1256D-40 | 1004.2 | Sheet flows with breccia, rare dikes, and alteration at (sub)greenschist facies conditions. | |
| Sheeted dike complex | Upper dikes | 309-1256D-129R-1, 0 cm | 1256D-44a | 1060.9 | Massive basalt, common subvertical intrusive contacts. Elevated P-wave velocity and thermal conductivity. |
| Granoblastic dikes | 312-1256D-192R-1, 0 cm | 1256D-78 | 1348.3 | Granoblastic texture; equant grains; secondary clinopyroxene, orthopyroxene, plagioclase, hornblende, magnetite, and ilmenite. | |
| Plutonic section | Gabbro 1 | 312-1256D-213R-1 (Piece 13, 52 cm) | 1256D-81 | 1406.62 | Medium-grained, generally orthopyroxene-bearing gabbroic rocks intrude overlying dikes: olivine gabbro, gabbro, and (disseminated) oxide gabbro, intruded by oxide gabbro to oxide quartz diorite. |
| Dike screen 1 | 312-1256D-225R-1 (Piece 1, 0 cm) | 1256D-90 | 1458.9 | Fine-grained to cryptocrystalline basalt dikes. Highly altered; granoblastic texture; secondary clinopyroxene, orthopyroxene, plagioclase, magnetite, ilmenite, and hornblende. | |
| Gabbro 2 | 312-1256D-230R-1 (Piece 5, 15 cm) | 1256D-91 | 1483.1 | Plutonic rock intrudes dike screen; medium-grained disseminated oxide gabbronorite with subordinate oxide gabbro, intruded by oxide gabbro, (oxide) diorite, and oxide quartz diorite veins; all highly altered; stoped basalt. | |
| Dike screen 2 | 312-1256D-232R-2 (Piece 9, 98 cm) | 1256D-94 | 1494.9 | Fine-grained granoblastic basalt (Unit 1256D-94) may have igneous or metamorphic origin. Unrecrystallized greenschist-facies late dike (Unit 1256D-95) at 1502.6 mbsf. Strongly to completely recrystallized granoblastic basalts containing minor oxide diorite patches; subordinate quartz diorite and tonalite (Unit 1256D-96). Also includes granoblastic basalts intruded by oxide gabbro to tonalite patches, veins, and dikelets and with minor (<3%) gabbroic rocks, from the “junkyards” at ~1500–1521.6 mbsf. | |
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