doi:10.2204/iodp.pr.312.2006

Superfast Spreading Rate Crust 3

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
• SHIPBOARD PARTICIPANTS
  • Expedition Scientists
  • Transocean Officials
  • IODP Shipboard Personnel and Technical Representatives
• 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
• SCIENTIFIC RESULTS
  • Predrilling Experiments during Expedition 309
  • Ocean Crust formed at Superfast Spreading Rate: Deep Drilling the Ocean Basement in Hole 1256D
• CONCLUSIONS
• PRELIMINARY ASSESSMENTS
  • Preliminary Operational Assessment of Expedition 309
  • Preliminary Operational Assessment of Expedition 312
  • Preliminary Scientific Assessment of Expedition 309
  • Preliminary Scientific Assessment of Expedition 312
• OPERATIONS
  • Expedition 309
  • Expedition 312
• REFERENCES
• TABLES
  • Table T1. Predicted depths to gabbros at Site 1256.
  • Table T2. Key parameters for Hole 1256D and preliminary subdivisions of the upper oceanic crust at Site 1256 adopted for Expeditions 309 and 312.
  • Table T3. Summary of results of Expedition 312 Vertical Seismic Profile experiment in Hole 1256D.
  • Table T4. Hole 1256D operations conducted during Expedition 309.
  • Table T5. Summary of coring bits used on Expedition 309.
  • Table T6. Operations Summary, Expedition 312.
• FIGURES
  • Figure F1. Basement age versus depth of basement penetration.
  • Figure F2. Age map of the Cocos plate and corresponding regions of the Pacific plate.
  • Figure F3. Depth to axial low-velocity zone plotted against spreading rate.
  • Figure F4. Reconstruction of Site 1256 and vicinity at 14 Ma.
  • Figure F5. Details of isochrons inferred from magnetic anomalies near Site 1256.
  • Figure F6. Site survey MCS data.
  • Figure F7. One-dimensional velocity model based on inversion of refraction data.
  • Figure F8. Contour map of seismic P-wave velocity at the top of basement.
  • Figure F9. Lithology schematics and chemical and logging results, Leg 206.
  • Figure F10. Distribution of alteration zones.
  • Figure F11. Time predicted for drilling and wireline logging operations.
  • Figure F12. Summary of drilling progress during Leg 206 and Expeditions 309 and 312.
  • Figure F13. Boreholes >200 m deep drilled into in situ ocean crust compared to Hole 1256D.
  • Figure F14. Simplified igneous stratigraphy.
  • Figure F15. Summary of basement stratigraphy.
  • Figure F16. Basalt typical of interior of sheet flows.
  • Figure F17. Sparsely olivine-clinopyroxene-plagioclase phyric microcrystalline basalt sheet flow.
  • Figure F18. Holocrystalline fine-grained gabbroic xenolith in an aphyric microcrystalline basaltic sheet flow.
  • Figure F19. Typical aphyric fine-grained massive basalt.
  • Figure F20. Sparsely plagioclase-olivine phyric moderately vesicular microcrystalline basalt.
  • Figure F21. Intergranular texture in massive fine-grained basalt.
  • Figure F22. Cryptocrystalline basalt clasts embedded in fine- to medium-grained cataclastic massive unit.
  • Figure F23. Mineralized volcanic breccia.
  • Figure F24. Holocrystalline, intergranular texture.
  • Figure F25. Cryptocrystalline chilled margin.
  • Figure F26. Units and dike subdivisions.
  • Figure F27. Sulfide-impregnated dike margin breccia.
  • Figure F28. Three complex intrusive contacts.
  • Figure F29. Expedition 309 and Leg 206 phenocryst data.
  • Figure F30. Intersertal to radiate texture.
  • Figure F31. Typical sample from Gabbro 1.
  • Figure F32. Typical Gabbro 2.
  • Figure F33. Contact between basalt dike and Unit 1256D-91.
  • Figure F34. Plots of whole-rock chemical composition.
  • Figure F35. Plots of all elements versus MgO.
  • Figure F36. Sc/Y versus Sr/Y.
  • Figure F37. Zr versus Y and Zr versus TiO2.
  • Figure F38. EPR MORB normalized multielement plot.
  • Figure F39. Comparison of incompatible element ratios versus MgO, Hole 504B.
  • Figure F40. Zr/TiO2 and Zr/Y ratios.
  • Figure F41. Alteration style and intensity.
  • Figure F42. Total volume percent of secondary minerals in veins.
  • Figure F43. Abundance of secondary mineral veins.
  • Figure F44. Mineral plot.
  • Figure F45. Variations in alteration.
  • Figure F46. Lithostratigraphy and alteration types, Holes 504B and 1256D.
  • Figure F47. Structural features and fracturing intensity.
  • Figure F48. Cataclastic zone at contact with clast of chilled basalt.
  • Figure F49. Variations in fracturing intensity.
  • Figure F50. Mineralized volcanic breccia.
  • Figure F51. Hyaloclastic breccias.
  • Figure F52. Cataclastic zone at dike contact.
  • Figure F53. Dips of structural features.
  • Figure F54. AF demagnetization of one of the most stable samples.
  • Figure F55. Intensity variation in demagnetized archive-half samples.
  • Figure F56. AF demagnetization of a sample typical of 1256Ð1400 mbsf.
  • Figure F57. AF demagnetization of a typical gabbro.
  • Figure F58. Inclination and declination.
  • Figure F59. NRM and magnetic susceptibility.
  • Figure F60. Discrete sample physical property results.
  • Figure F61. Variations in porosity.
  • Figure F62. Preliminary logging measurements.
  • Figure F63. TAP temperatures and FMS data.
  • Figure F64. Logging results for sheeted dikes and gabbro.
  • Figure F65. Bulk density and velocity from logs and discrete samples.
  • Figure F66. Whole-round and matching slab images.
  • Figure F67. Bit sub under tension.
  • Figure F68. Crack in the 5 inch drill pipe.
  • Figure F69. Used C-7 bit missing all of its cones.
• MOVIES
  • Movie M1. Video from the VIT showing the first reentry of Hole 1256D during Expedition 309.
  • Movie M2. Video from the VIT showing vigorous jet of drilling mud exiting the 5 inch pipe from a crack.
  • Movie M3. Video from the VIT showing the tenth reentry (ninth RCB coring bit) of Hole 1256D during Expedition 309.

Publication date: 20 April 2006

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