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Accueil > Documents > Pages personnelles > Benoît ILDEFONSE > Recherche > En mer

En mer ...

Drilling Deep in the East Pacific Crust : ODP Hole 1256D, IODP Expedition 335

Pipe tripping ...

Integrated Ocean Drilling Program (IODP) Expedition 335 “Superfast Spreading Rate Crust 4” returned to deepen Ocean Drilling Program (ODP) Hole 1256D several hundred meters into cumulate gabbros to understand the formation of ocean crust accreted at fast spreading ridges. Site 1256 is located in 15 Ma crust formed at the East Pacific Rise during an episode of superfast ocean spreading (>200 mm/yr full rate) and exploits the inverse relationship between spreading rate and the depth to seismically imaged magma chambers at modern mid-ocean ridges. Three earlier cruises to Hole 1256D have drilled 1507 m through the sediments, lavas and dikes and 100 m into a complex dike-gabbro transition zone. The specific objectives of IODP Expedition 335 were to : (1) test models of magmatic accretion at fast spreading ocean ridges ; (2) quantify the vigor of hydrothermal cooling of the lower crust ; (3) establish the geological meaning of the seismic Layer 2-3 boundary ; and (4) estimate the contribution of lower crustal gabbros to marine magnetic anomalies.

Operations proved challenging from the outset with almost three weeks spent re-opening and securing unstable sections of Hole 1256D. When coring commenced, the absolute destruction of a hard-formation C9 rotary coring bit required further remedial operations to remove junk and huge volumes of accumulated drill cuttings. A minor advance to 1522 mbsf was achieved. Hole-cleaning operations returned large (up to 3.5 kg) samples that preserve hitherto unseen magmatic, hydrothermal and structural relationships. The dike-gabbro transition zone sampled in Hole 1256D to date is over 170 m thick, of which >100 m are contact metamorphosed granoblastic basalts. This zone records a dynamically evolving thermal boundary between the principally hydrothermal domain of the upper crust and a deeper zone of intrusive magmatism. The samples document intimate coupling between temporally and spatially intercalated intrusive, hydrothermal, contact metamorphic, partial melting and retrogressive processes.

Although operational difficulties precluded the achievement of primary objectives, Hole 1256D has been thoroughly cleared of junk and drill cuttings that have hampered operations during this and previous Expeditions. At the end of Expedition 335, we briefly resumed coring and stabilized problematic intervals with cement. Hole 1256D is open to its full depth. Deepening this important reference hole into intact ocean crust should be undertaken in the near future to achieve long standing primary goals of scientific ocean drilling.


References :
- Teagle, D.A.H., Ildefonse, B., Blum, P., and the IODP Expedition 335 Scientists, 2012. Proc. IODP, 335 : College Station TX (Integrated Ocean Drilling Program Management International, Inc.). in press.
- Teagle, D.A.H., Ildefonse, B., Blum, P., and the IODP Expedition 335 Shipboard Scientists, 2012. Battling through the thermal boundary layer : Deep sampling in ODP Hole 1256D during IODP Expedition 335. Scientific Drilling, in press.
- Koepke, J., France, L., Mueller, T., Faure, F., Goetze, N., Dziony, W., Ildefonse, B., 2011. Gabbros from IODP Site 1256, equatorial Pacific : Insight into axial magma chamber processes at fast spreading ocean ridges. Geochemistry Geophysics Geosystems 12, Q09014. doi:10.1029/2011gc003655
- Teagle, D.A.H., Ildefonse, B., Blum, P., Scientists, I.E.S., 2011. Battling through the thermal boundary layer : Deep sampling in ODP Hole 1256D during IODP Expedition 335. InterRidge News 20, 12-17
- Teagle, D., Ildefonse, B., 2011. Journey to the mantle of the Earth. Nature 471, 437-439. doi:10.1038/471437a
- Ildefonse, B., Teagle, D.A.H., Blum, P., and IODP Expedition 335 Scientists, 2011. Battling through the thermal boundary layer : Deep sampling in ODP Hole 1256D during IODP Expedition 335 (Invited). Abstract V13F-01 presented at 2011 Fall Meeting, AGU, San Francisco, Calif., 3-9 Dec.
- France, L., Koepke, J., Ildefonse, B., Cichy, S.B., Deschamps, F., 2010. Hydrous partial melting in the sheeted dike complex at fast spreading ridges : experimental and natural observations. Contributions to Mineralogy and Petrology 160, 683-704. doi:10.1007/s00410-010-0502-6
- France L., Ildefonse B., Koepke J., Bech F., 2010. A New Method to Estimate the Oxidation State of Basaltic Series from Microprobe Analyses. Journal of Volcanology and Geothermal Research, 189, 340-346. doi:10.1016/j.jvolgeores.2009.11.023
- Violay, M., Pezard, P.A., Ildefonse, B., Belghoul, A., Laverne, C., 2010. Petrophysical properties of the root zone of sheeted dikes in the ocean crust : A case study from Hole ODP/IODP 1256D, Eastern Equatorial Pacific. Tectonophysics 493, 139–152. doi:10.1016/j.tecto.2010.07.013
- France L., Ildefonse B., Koepke J., Godard M. & MacLeod C., 2010. Melting the Hydrothermally Altered Sheeted Dike Complex : Chemical Composition of the Main MORB Crustal Contaminant. Goldschmidt 2010, June 13-18, Knoxville, Tenessee.
- France, L., Ildefonse, B., and Koepke, J., 2009. Interactions between magma and hydrothermal system in Oman ophiolite and in IODP Hole 1256D : fossilization of a dynamic melt lens at fast spreading ridges. Geochem. Geophys. Geosyst., 10, Q10O19, doi:10.1029/2009GC002652
- France, L., Ildefonse, B., Koepke, J., MacLeod, C.J., and Godard, M., 2009, Melting the Hydrothermally Altered Sheeted Dike Complex : Experiments and Chemical Compositions, Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract OS11B-07
- France, L., Ildefonse, B., and Koepke, J., 2009. Dynamics of the Axial Melt Lens/Dike transition at fast spreading ridges : assimilation and hydrous partial melting. EGU General Assembly 2009, Vienna (Austria), April 19-24, 2009. Geophysical Research Abstracts, Vol. 11, EGU2009-10159.
- Violay, M., Pezard, P.A., Ildefonse, B., Belghoul, A., and Mainprice, D., 2009. Petrophysical characterization of the hydrothermal root zone in the sheeted dike complex from IODP Hole 1256D. Geophysical Research Abstracts, Vol. 11, EGU2009-5636.
- France, L., Ildefonse, B., and Koepke, J., 2008. The fossilisation of a dynamic melt lens at fast spreading centers : insights from the Oman ophiolite. Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract V51F-2111.
- France, L., Ildefonse, B., Koepke, J., Cordier, C., and Bech, F., 2008. A new method to constrain the oxidation state of basaltic series from microprobe analysis. Geophysical Research Abstracts, Vol. 10, EGU2008-A-04345, 2008. SRef-ID : 1607-7962/gra/EGU2008-A-04345
- France, L., Ildefonse, B., and Koepke, J., 2008. Processes governing the magmatic-hydrothermal interface at the sheeted dike complex-gabbro transition : From the comparison between the IODP Hole 1256D and the Oman ophiolite to a general model ? Geophysical Research Abstracts, Vol. 10, EGU2008-A-04325, 2008. SRef-ID : 1607-7962/gra/EGU2008-A-04325