Figure F1. Scientific drilling of the oceanic lithosphere, 19682003. World map of the oceans showing the distribution of drill holes into in situ ocean basement formed at mid-ocean ridges. Despite more than 30 yr of ocean drilling, there are still relatively few drill holes in oceanic crust and a very poor sampling distribution in terms of basement depth, crustal age, and spreading rate. Note the clustering of drill sites along the Mid-Atlantic Ridge and in the eastern Pacific Ocean. Stars = holes drilled by DSDP and ODP.
Figure F2. Basement age vs. depth of basement penetration for scientific drill holes deeper than 50 m drilled into in situ ocean crust formed at the mid-ocean ridges. Note the boundaries between the erupted lavas, dikelava transition zone, and the sheeted dike complex/upper gabbro boundary are placed at arbitrary depths based loosely on the Hole 504B stratigraphy. Predictions based on marine seismic reflection studies indicate that the combined thickness of the lava-dike sequences should decrease with spreading rate but are yet to be tested, and whether it is the dikes or lavas that is thinned is so far unknown. Black lines = DSDP drill holes, dark blue lines = ODP drill holes, red lines = Holes 1256C and 1256D drilled into basement during Leg 206.
Figure F3. Depth of penetration of drill holes into in situ basement subdivided by ocean basin. Black lines = DSDP drill holes, dark blue lines = ODP drill holes, red lines = Holes 1256C and 1256D drilled into basement during Leg 206.
Figure F4. Depth of penetration of drill holes into in situ basement clustered by broad spreading rate subdivisions where slow < 40 mm/yr < moderate < fast. Black lines = DSDP drill holes, dark blue lines = ODP drill holes, red lines = Holes 1256C and 1256D drilled into basement during Leg 206.
Figure F5. Schematic cross section of oceanic crust created by superfast seafloor spreading (after Karson et al., 2002). Approximate boundaries of seismic layers are given to the left. Black arrows = magma withdrawal in the subaxial magma chamber, yellow arrows =e deformation related to faulting, fracturing, and block rotation in the sheeted dikes and lower lavas.
Figure F6. Depth to axial low-velocity zone plotted against spreading rate, modified from Purdy et al. (1992) and Carbotte et al. (1997). Depth vs. rate predictions from two models of Phipps Morgan and Chen (1993) are shown, extrapolated subjectively to 200 mm/yr.
Figure F7. Age map of the Cocos plate and corresponding regions of the Pacific plate. Isochrons at 5-m.y. intervals have been converted from magnetic anomaly identifications according to the timescale of Cande and Kent (1995). Selected DSDP and ODP sites that reached basement are indicated by circles. The wide spacing of 10- to 20-m.y. isochrons to the south reflects the extremely fast (200220 mm/yr) full spreading rate. Dashed boxes show locations of figures showing details of magnetic anomalies near Site 1256 (Fig. F8) and the Alijos Rocks survey area (Fig. F13). FZ = fracture zone.
Figure F8. Details of isochrons inferred from magnetic anomalies near Site 1256. Gray shading shows normal magnetic polarity, based on digitized reversal boundaries (small circles, after Wilson, 1996). Bold line shows location of Guatemala basin MCS tracklines from the site survey conducted in MarchApril 1999. Anomaly ages: 5A = ~12 Ma, 5B = ~15 Ma, and 5D = ~17 Ma.
Figure F9. Reconstruction of Site 1256 and vicinity at 14 Ma, ~1 m.y. after formation of the site at the East Pacific Rise. Positions and plate velocities (arrows labeled in millimeters per year) are relative to the Antarctic plate, which is reasonably fixed relative to the spin axis and hotspots. Reconstructed positions of mapped magnetic Anomalies 5B, 5C, and 6 (ages 1520 Ma), and existing DSDP/ODP drill sites are shown by shaded bars and circles, respectively.
Figure F10. Bathymetry and site survey track map for Site 1256 (proposed Site GUATB-03). Abyssal hill relief of up to 100 m is apparent in the southwest part of the area; relief to the northeast is lower and less organized. Line numbers 2128 identify multichannel seismic (MCS) lines for subsequent figures. Triangles = locations of ocean-bottom hydrophones (OBHs) recovered with data.
Figure F11. Underway geophysics plotted perpendicular to track line for the Guatemala Basin sites. A. Magnetic anomaly, with negative anomaly (normal polarity) shaded and identifications labeled. B. Center-beam bathymetry. C. Free-air gravity anomaly.
Figure F12. Bathymetry and track maps for proposed alternate Site GUATB-01. Site GUATB-01 has very shallow depths and low relief, excluding seamounts, in contrast to proposed Site ALIJOS (Fig. F13), which is slightly deep and has very high relief. MCS = multichannel seismic survey.
Figure F13. Bathymetry and track maps for proposed Site ALIJOS, a surveyed site that was not drilled.
Figure F14. Stacked, migrated section of MCS data from line 22, showing positions of primary proposed drill Site GUATB-03C and proposed alternate Site GUATB-03B. Crossing positions of lines 2428 are labeled.
Figure F15. Stacked, migrated section of MCS data from line 27, showing the primary proposed drill Site GUATB-03C and crossing positions of lines 2123. The bright reflector at 5.55.7 s near the line 21 crossing may be a thrust fault, and site selection decisions avoided this feature.
Figure F16. One-dimensional velocity model based on inversion of refraction data. At shallow depths, separate inversions were performed on northeast and southwest data subsets, with slightly faster velocities found to the northeast where abyssal hill topography is very subdued. The Layer 2/3 boundary is present in the depth range 1.21.5 km. The velocity model of Detrick et al. (1998) for Site 504, also based on ocean-bottom hydrophone refraction, is shown for comparison. Apparent differences are dominated by differences in the inversion techniques, but the differences at 1.31.7 km may be barely above uncertainty.
Figure F17. Location map showing relative positions of the four holes drilled at Site 1256.
Figure F18. Schematic of the reentry cone and casing installed in Hole 1256D. TOC = top of casing, ID = inner diameter, TD = total depth.
Figure F19. Simplified lithostratigraphic column for Site 1256. The lithology column gives the approximate relative abundance of major components (>10%) contributing to the rock name, following the conventions used for the AppleCore core description sheets.
Figure F20. The magnetostratigraphy and the inclination and declination of the cored interval as estimated from stable endpoints from split-core sections. Also shown is the intensity of magnetization following 30-mT alternating-field demagnetization. The brackets indicate intervals where the interpretation is uncertain. Orange box = an interval where the magnetic polarity could not be determined.
Figure F21. The magnetostratigraphy and declination of the cored interval as estimated from principal component analysis (PCA) and stable endpoints (SEP) from split-core sections and discrete samples.
Figure F22. Age-depth plot of Neogene calcareous nannofossil datums (diamonds) and geomagnetic reversals (squares) from Hole 1256B. Nannofossil datum ages and depths are given in Table T7 (see also "Biostratigraphy"), and geomagnetic reversal ages and depths are given in Table T9 (see also "Paleomagnetism"). FO = first occurrence, LO = last occurrence.
Figure F23. Sedimentation rates as constrained by the magnetostratigraphy, biostratigraphy, and a linear sedimentation rate model. The linear rates are shown extrapolated to basement.
Figure F24. Depth profiles of calcium carbonate, organic carbon, terrigenous matter, and biogenic silica in sediments.
Figure F25. Depth and age profile of Ba/Ti ratios, a chemical proxy for productivity, in sediments.
Figure F26. Depth profiles of Mg/Ca, Sr/Ca, K/Ca and K/Mg, and Li/Mg and Li/Ca. JDF = values observed at Juan de Fuca Ridge flank, representing basement fluid. SW = seawater values. Mg/Ca and K/Ca displays diffusion between seawater and basement fluids. Sr/Ca values are larger than what is observed at Juan de Fuca Ridge flank, suggesting a strong influence of recrystallization taking place. Li/Mg and Li/Ca ratios are similar to Mg/Ca profile.
Figure F27. Whole-core gamma ray attenuation (GRA) bulk density, discrete sample bulk density, and grain density, porosity, and split-core P-wave velocity (PWS3) for the sediments of Site 1256. Open symbols = anomalous values. Also shown is the simplified lithostratigraphy, blue = nannofossil ooze, orange and yellow = clay, silt, or silty clay, shades of purple = diatom-rich intervals. Dashed lines = the boundary between lithologic Units I and II at 40.6 mbsf, the top of the diatom mat at 111 mbsf, and a physical property boundary at ~205 mbsf. The GRA density data have been smoothed by averaging over a 41-point (102.5 cm long) window.
Figure F28. Downhole variations in temperature, thermal conductivity, and heat flow for Hole 1256B.
Figure F29. Summary of basement stratigraphy at Site 1256 showing (from left) depth, core, recovered intervals, unit and subunit boundaries, igneous lithology, groundmass grain size, and phenocryst percentages based on thin section descriptions for Holes 1256C and 1256D.
Figure F30. Typical aphyric cryptocrystalline to microcrystalline texture of sheet flow interior (top) with decreasing grain size toward the chilled margin at the base of the piece in basement Unit 1256C-6 (interval 206-1256C-6R-5, 1335 cm).
Figure F31. Folded recrystallized material at base of ponded flow in basement Unit 1256C-18i (interval 206-1256C-11R-7, 2142 cm).
Figure F32. Typical textures of massive lavas and thin sheet flows. A. Interior of massive lava (interval 206-1256C-10R-4, 114 cm). B. Glassy margin of thin sheet flow in basement Unit 1256D-2 (interval 206-1256D-13R-3, 2533 cm). Note the horizontal planar shape to glassy margin and parallel vesicle horizon just below the margin.
Figure F33. Pieces of hyaloclastite consisting of rounded glassy blocks with chilled margins and angular clasts of glass in basement Unit 1256D-21 (intervals 206-1256D-51R-1, 106150 cm).
Figure F34. Volcaniclastic rock composed of angular fragments of cryptocrystalline basalt embedded in a matrix of altered glass in basement Unit 1256D-4a (interval 206-1256D-20R-1, 3150 cm).
Figure F35. Modal abundance of phenocrysts in basalt from Holes 1256C (solid line), 1256D (broken line), and all of Site 1256 (thick broken line). Lava flows and dikes from Hole 504B (dotted line) and the Mid-Atlantic Ridge (MAR) (thick line) are plotted for comparison.
Figure F36. Proportion of phenocrystic clinopyroxene-plagioclase-olivine in basalt from Holes 1256C and 1256D in comparison with Hole 504B and the Mid-Atlantic Ridge (MAR).
Figure F37. Plagioclase phenocryst clots (Sample 206-1256D-55R-2, 6364 cm) (width of view = 0.7 mm). A. Normally zoned plagioclase partially enclosing augite microphenocrysts. B. Reversely zoned plagioclase clotted with augite and olivine. Note that augite microphenocrysts are not in direct contact with the riddled, resorbed core of plagioclase.
Figure F38. Plots of shipboard geochemistry analyses vs. depth with igneous stratigraphy and units for comparison. Dashed lines = Hole 1256C unit boundaries, solid lines = Hole 1256D unit boundaries, h = hyaloclastite, a = altered basalt.
Figure F39. Nb-Zr-Y ternary diagram showing the fields for different basalt types. Samples taken from Site 1256 all lie in the N-MORB field. E-MORB = enriched mid-ocean-ridge basalt, N-MORB = normal mid-ocean-ridge basalt. Open squares = Hole 1256C, open diamonds = Hole 1256D, solid diamonds = Unit 1256D-1, crosses = Unit 1256C-18, open triangles = Hole 1256D high-Zr samples, solid triangles = Hole 1256D hyaloclastite samples, solid circles = Hole 1256D altered basalt.
Figure F40. Zr vs. TiO2 and Nb. Open squares = Hole 1256C, open diamonds = Hole 1256D, solid diamonds = Unit 1256D-1, crosses = Unit 1256C-18, open triangles = Hole 1256D high-Zr samples, solid triangles = Hole 1256D hyaloclastite samples, solid circles = Hole 1256D altered basalt.
Figure F41. Plots of elemental abundance vs. MgO for all shipboard analyses.
Figure F42. Distributions of alteration types with depth in Hole 1256D. Data are averaged for each core and plotted vs. depth to the top of the core.
Figure F43. Distribution of secondary minerals with depth in Hole 1256D. Lines reflect presence or absence of a phase only. Note the late magmatic/hydrothermal minerals at 275350 mbsf in massive Unit 1 and the appearance of secondary albite below 625 mbsf.
Figure F44. Total volume percent secondary minerals contained in veins, breccia, and interflow sediment with depth in Hole 1256D. Data for each core are plotted vs. depth to the top of the core.
Figure F45. Abundance of secondary mineral veins with depth in Hole 1256D. Numbers of veins per core are normalized to the amount of recovered material per core (veins per meter) and plotted vs. depth to the top of the core.
Figure F46. Volume percent secondary mineral veins with depth in Hole 1256D. Area percentages of veins on cut core surfaces are normalized to amount of recovered material per core, and area percentages are assumed equal to volume percentages, which are plotted vs. depth to the top of the core.
Figure F47. Distribution of alteration zones with depth in selected ODP basement sections (after J. Alt, unpubl. data). Hole 1256D is shown for comparison.
Figure F48. Occurrence of measured structure with depth, Holes 1256C and 1256D.
Figure F49. Rose diagrams of true dip values of all oriented structures for Holes 1256C and 1256D.
Figure F50. Thermal demagnetization plots for Sample 206-1256D-24R-2, 1820 cm, a sample with relatively high blocking temperatures and little drilling overprint. Component plot at upper right shows north and east horizontal components as solid symbols and total horizontal and vertical components as open symbols.
Figure F51. Alternating-field demagnetization plots for Sample 206-1256C-11R-3, 6264 cm. This exceptionally stable sample appears to have the drilling overprint removed by 14 mT. Component plot at upper right shows north and east horizontal components as solid symbols and total horizontal and vertical components as open symbols.
Figure F52. Summary of downhole logging results in Hole 1256C and 1256D; caliper, total gamma ray emission, porosity, formation capture cross section, density, photoelectric effect, electrical resistivity, straight FMS and UBI images (not oriented) are shown. Laboratory physical property measurements of the porosity and bulk density are also plotted along with the graphic lithology log based on core descriptions in Hole 1256B.
Figure F53. A comparison between unrolled core images from the massive ponded basalt (Unit 1c) recovered in Section 206-1256D-6R-5 and FMS/UBI images from ~300 mbsf. Several features can be identified as potential matches on the whole-round core image and in the oriented image logs. The depth scale shown is the ODP curated depth, and core pieces have not been reoriented with respect to the FMS/UBI images because the DMT CoreLog Integra software that performs this routine was not functional during Leg 206.
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