Table T35. Igneous unit and contact log, Hole 1256D, Expedition 312.
| Unit | Upper contact | Nature of contact/ Rationale for boundary |
Minimum thickness (m) |
Rock type | Thin section |
|
|---|---|---|---|---|---|---|
| Core, section, piece, interval (cm) |
Depth (mbsf) |
|||||
| 312-1256D- | ||||||
| 1256D-66 | 172R-1 (Piece 1, 0) | 1255.10 | Likely continues Unit 1256D-65 from Expedition 309. | 1.74 | Sparsely plagioclase-phyric to aphyric fine-grained basalt. | 1, 2, 3 |
| 1256D-67 | 174R-1 (Piece 5, 25) | 1265.65 | Mixed material from Units 1256D-66 and 68. | 0.27 | Mixed aphanitic and fine-grained basalts. | |
| 1256D-68 | 174R-1 (Piece 11, 57) | 1265.97 | Textural change—prominent acicular plagioclase. | 0.73 | Aphyric fine-grained basalt. | 4, 5, 6 |
| 1256D-68/69 | 175R-1 (Piece 1, 0) | 1271.30 | Mixed rubble Units 1256D-86 and 69. | 0.34 | Mixed aphyric fine-grained and cryptocrystalline to fine-grained basalt. | 7 |
| 1256D-69 | 175R-1 (Piece 12, 47) | 1271.77 | Cryptox. chilled margin material 1271.3–1272.0 mbsf, with subvertical contact exposed in Pieces 11 and 12, ~1271.75 mbsf. Complete cooling unit with fine-grained center and cryptox lower zone, ~1277 mbsf, but no lower contact. | 1.39 | Aphyric cryptocrystalline to fine-grained basalt. | 8, 9, 10, 11 |
| 1256D-70 | 176R-1 (Piece 25, 106) | 1277.16 | Textural change—prominent acicular plagioclase. | 0.37 | Aphyric microcrystalline to fine-grained basalt. | 12 |
| 1256D-71 | 176R-1 (Piece 33, 145) | 1277.55 | Brecciated basalt dike margin. | 0.09 | Aphyric cryptocrystalline basalt. | 13, 14 |
| 1256D-72 | 176R-2 (Piece 4, 17) | 1277.77 | Textural change—uniform, aphyric fine grained. | 0.68 | Aphyric fine-grained basalt. | 15, 16 |
| 1256D-73 | 177R-1 (Piece 1, 0) | 1280.90 | Textural change. Mostly fine-grained with short cryptocrystalline intervals, including multiple intrusive contacts at 1290.5 and 1295.3 mbsf. | 1.71 | Aphyric microcrystalline to fine-grained basalt. | 17, 18, 19, 20, 21 |
| 1256D-74 | 182R-1 (Piece 5, 15) | 1305.05 | Textural change. Microcrystalline, but coarsens downhole. | 1.27 | Aphyric microcrystalline basalt. | 22, 23, 24 |
| 1256D-75a | 186R-1 (Piece 1, 0) | 1319.50 | No upper contact. Intruded lower contact. | 1.65 | Aphyric microcrystalline to fine-grained basalt. | |
| 1256D-75b | 186R-1 (Piece 10,11) | — | Thin dike intruding into Unit 1256D-75a. | — | Aphyric cryptocrystalline basalt. <1cm aphanitic dike in Pieces 10 and 11, ~1320 mbsf. | 25, 26, 27 |
| 1256D-76 | 187R-1 (Piece 17, 71) | 1325.01 | Intrusive into Unit 1256D-75. Complete grain size–graded cooling unit. No lower contact. | 1.58 | Aphyric cryptocrystalline to microcrystalline basalt. | 28, 29 |
| 1256D-77 | 188R-1 (Piece 1, 0) | 1329.10 | Incomplete grain size–graded cooling unit. No contacts. | 1.20 | Aphanitic basalt rubble. | 30, 31 |
| 1256D-78 | 192R-1 (Piece 1, 0) | 1348.30 | Textural change—low recovery rubble. | 1.56 | Aphyric microcrystalline basalt rubble. | 32–39 (40–46 in ghost core 201G) |
| 1256D-79 | 202R-1 (Piece 1, 0) | 1372.80 | Hiatus in drilling and recovery above. | 0.41 | Aphyric fine-grained basalt. | |
| 1256D-80a | 202R-1 (Piece 4, 44) | 1373.24 | Sharp change in grain size in recovered rocks. | 1.42 | Aphyric cryptocrystalline basalt. | 47–56, 58, 104, 118 |
| 1256D-80b | 212-1 (Piece 5, 6) | — | Igneous contact, both sides exposed. | — | Fine-grained trondhjemite. | 57, 104 |
| 1256D-81 | 213R-1 (Piece 13, 52) | 1406.62 | Intrusive contact—little change in grain size, intrusive gabbro toward the margin. | 0.18 | Mixed dike and medium-grained oxide gabbro. | 59, 65 |
| 1256D-82 | 214R-1 (Piece 9, 31) | 1411.21 | Igneous contact—variation in grain size and lithology. | 0.79 | Medium-grained quartz-rich oxide diorite (FeTi diorite). | 60, 62, 65, |
| 1256D-83 | 214R-1 (Piece 15, 75) | 1411.65 | Igneous contact—sharp change in color/texture. | 0.26 | Medium-grained disseminated oxide gabbro. | 61, 66, 67 |
| 1256D-84 | 214R-1 (Piece 26, 132) | 1412.22 | Igneous contact (with Unit 1256D-82)—sharp change in color/texture. | 0.29 | Medium-grained disseminated oxide gabbro. | 63, 68, 69, |
| 1256D-85 | 214R-2 (Piece 7, 32) | 1412.67 | Change in texture to rounded patches. | 2.49 | Medium-grained patchy gabbro. | 64, 70–74, 119 |
| 1256D-86a | 215R-2 (Piece 9, 35) | 1416.10 | Change in texture to poikilitic clinopyroxene. | 1.7 | Medium-grained gabbro. | 75–77 |
| 1256D-86b | 216R-1 (Piece 19, 88) | 1427.20 | Igneous contact—coarser pale plagioclase. | — | 75 | |
| 1256D-87 | 216R-1 (Piece 134, 26) | 1434.80 | Change in size of poikilitic clinopyroxene to >1 cm. | 0.37 | Medium-grained gabbro. | 78 |
| 1256D-88 | 217R-1 (Piece 11, 44) | 1422.00 | Downhole appearance of coarser diffuse portions with pale plagioclase. | 7.29 | Medium-grained gabbro. | 79–88 |
| 1256D-89a | 223R-2 (Piece 1, 0) | 1450.80 | Rapid grain size decrease. | 1.56 | Medium-grained gabbro. | 89–96 |
| 1256D-89b | 223R-2 (Piece 1, 39) | 1451.20 | Intrusive contact—less diffuse and straighter than those observed in the patches in Unit 1256D-88. | — | Coarse-grained disseminated oxide gabbro. | |
| 1256D-90a | 225R-1 (Piece 1, 0) | 1458.90 | Lithology change. | 2.59 | Fine-grained to cryptocrystalline aphyric basalt. | 97–101, 103, 105–107 |
| 1256D-90b | 227R-1 (Piece 3, 12) | 1468.60 | Intrusive contact. | — | Medium-grained quartz diorite. | 99 |
| 1256D-90c, d | 227R-1 (Piece 13, 83) | 1469.30 | Intrusive contact. | — | C = fine-grained tonalite. D = medium-grained gabbro. | 101, 102 |
| 1256D-90e | 227R-2 (Piece 1, 0) | 1470.00 | Intrusive contact. | — | Medium-grained gabbro. | 105 |
| 1256D-90f | 227R-2 (Piece 11, 61) | 1470.60 | Intrusive contact. | — | Fine-grained tonalite. | 103 |
| 1256D-91a | 230R-1 (Piece 5, 15) | 1483.11 | Sharp change in grain size (fine grained to medium grained)—invasive into Unit 1256D-90. | 1.16 | Medium-grained oxide gabbro with basaltic fragments. | 106, 108–110 |
| 1256D-91b | 230R-1 (Piece 11, 111) | 1484.11 | Igneous contact—sutured contact. | — | Medium-grained leuco-gabbro intrusive (~10 mm wide). | 109 |
| 1256D-92a | 230R-1 (Piece 12, 131) | 1484.31 | Textural change—disappearance of basaltic fragment. | 7.89 | Medium-grained orthopyroxene-bearing gabbro. | 111–113 |
| 1256D-92b | 231R-1 (Piece 2, 23) | 1488.13 | Intrusive contact—cut at a high angle through Unit 1256D-92a. | — | Medium-grained leuco-gabbro dike (~1 cm). | |
| 1256D-92c | 231R-4 (Piece 6, 65) | 1492.58 | Igneous contact—mostly sharp (but partly diffuse). | — | Medium-grained quartz diorite (no chilled margin, 1 cm wide). | |
| 1256D-92d | 232R-2 (Piece 1, 0) | 1493.98 | Igneous contact—sutured contact. | — | Medium-grained oxide-bearing quartz gabbro. | 114 |
| 1256D-93 | 232R-2 (Piece 2, 4) | 1494.02 | Textural change—reappearance of rounded basaltic xenoliths toward boundary. | 0.39 | Medium-grained gabbro. | 115,116 |
| 1256D-94 | 232R-2 (Piece 9, 97) | 1494.95 | Intrusive contact—intruded by Unit 1256D-93 gabbro. | 0.25 | Aphyric fine-grained basalt with granoblastic texture. | 116,120 |
| 1256D-95 | 234R-1 (Piece 4, 10) | 1502.60 | Textural change—lighter color, finer grained. | 0.16 | Aphyric microcrystalline basalt, no metamorphic texture in thin section. | 117 |
Note: — = not applicable.
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