doi:10.2204/iodp.pr.309.2005

Superfast Spreading Rate Crust 2

A complete in situ section of upper oceanic crust formed at a superfast spreading rate

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Table of Contents

• TITLE PAGE
• PUBLISHER'S NOTES
• PARTICIPANTS
• ABSTRACT
• BACKGROUND AND OBJECTIVES
  • Rationale for Site Selection and Location Criteria for Deep Drilling
  • Site Selection
  • Geological Setting of Hole 1256D
  • Scientific Objectives of Expeditions 309 and 312
  • Principal Results of ODP Leg 206
  • Predictions of Depth to Gabbros
• OPERATIONS
• SCIENTIFIC RESULTS
  • Predrilling Experiments
  • Ocean Crust formed at Superfast Spreading Rate: Deep Drilling the Ocean Basement in Hole 1256D
• CONCLUSIONS
• PRELIMINARY ASSESSMENTS
  • Preliminary Operational Assessment
  • Preliminary Scientific Assessment
• REFERENCES
• TABLES
  • Table T1. Predicted depths to gabbros.
  • Table T2. Operations conducted during Expedition 309.
  • Table T3. Summary of coring bits used during Expedition 309.
  • Table T4. Key parameters and preliminary subdivisions of upper oceanic crust.
  • Table T5. Igneous unit and contact log.
• FIGURES
  • Figure F1. Basement age versus depth and depth of penetration.
  • Figure F2. Age map of the Cocos plate.
  • Figure F3. Depth to axial low-velocity zone.
  • Figure F4. Reconstruction of Site 1256 and vicinity.
  • Figure F5. Details of isochrons and bathymetry and site survey track map.
  • Figure F6. Site survey MCS data.
  • Figure F7. One-dimensional velocity model.
  • Figure F8. Contour map of seismic P-wave velocity and geological map of Site 1256 area.
  • Figure F9. Recovery and lithology schematics and selected chemical and logging results.
  • Figure F10. Distribution of alteration zones with depth.
  • Figure F11. Depth versus time predicted for drilling and wireline logging operations.
  • Figure F12. Bit sub under tension on the rotary table.
  • Figure F13. Crack found in the 5 inch drill pipe.
  • Figure F14. Drilling progress in Hole 1256D during Expedition 309.
  • Figure F15. Boreholes drilled into in situ ocean crust compared to Hole 1256D.
  • Figure F16. Simplified igneous stratigraphy, Hole 1256D.
  • Figure F17. Summary of basement stratigraphy, Hole 1256D.
  • Figure F18. Aphyric cryptocrystalline to microcrystalline basalt.
  • Figure F19. Sparsely olivine-clinopyroxene-plagioclase phyric microcrystalline basalt sheet flow.
  • Figure F20. Holocrystalline fine-grained gabbroic xenolith.
  • Figure F21. Typical aphyric fine-grained massive basalt.
  • Figure F22. Sparsely plagioclase-olivine phyric moderately vesicular microcrystalline basalt.
  • Figure F23. Intergranular texture in massive fine-grained basalt.
  • Figure F24. Cryptocrystalline basalt clasts.
  • Figure F25. Mineralized volcanic breccia and volcanic breccia interbedded with sheet flow.
  • Figure F26. Holocrystalline, intergranular texture.
  • Figure F27. Sulfide-impregnated dike margin breccia.
  • Figure F28. Three complex intrusive contacts.
  • Figure F29. Expedition 309 phenocryst content compared with Leg 206 phenocryst data.
  • Figure F30. Plots of whole-rock chemical composition versus depth.
  • Figure F31. Plots of all elements versus MgO.
  • Figure F32. Zr versus Y and Zr versus TiO2.
  • Figure F33. EPR MORB normalized multielement plot of lithologic subdivisions.
  • Figure F34. Comparison of incompatible element ratio versus MgO and basalt.
  • Figure F35. Zr/TiO2 and Zr/Y ratios.
  • Figure F36. Alteration style and intensity.
  • Figure F37. Total volume percent of secondary minerals.
  • Figure F38. Abundance of secondary mineral veins.
  • Figure F39. Mineral plot versus depth.
  • Figure F40. Distribution of structural features and variation of intensity of fracturing.
  • Figure F41. Cataclastic zone at contact with clast of chilled basalt.
  • Figure F42. Subtype of hyaloclastite.
  • Figure F43. Hyaloclastic breccias.
  • Figure F44. Cataclastic zone at dike contact.
  • Figure F45. Rose diagram of true dips of the dike contacts.
  • Figure F46. AF demagnetization behavior of stable sample.
  • Figure F47. Examples of intensity variation and histogram showing frequency of thickness.
  • Figure F48. Discrete sample results.
  • Figure F49. Variation in porosity with depth.
  • Figure F50. Average thermal conductivity.
  • Figure F51. Selected preliminary logging measurements.
  • Figure F52. Temperature profiles and FMS data.
  • Figure F53. Example of whole-round image and matching slab image.
• MOVIES
  • Movie M1. First reentry of Hole 1256D.
  • Movie M2. Vigorous jet of drilling mud exiting the 5 inch pipe.
  • Movie M3. Tenth reentry of Hole 1256D.