Leg 206 summary

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doi: 10.2973/odp.proc.ir.206.101.2003
Author(s): Wilson, Douglas S.; Teagle, Damon A. H.; Acton, Gary D.; Alt, Jeffrey C.; Banerjee, Neil R.; Barr, Samantha R.; Coggon, Rosalind; Cooper, Kari M.; Crispini, Laura; Einaudi, Florence; Jiang, Shijun; Kalberkamp, Ulrich; Kerneklian, Marcie; Laverne, Christine; Nichols, Holly J.; Sandwell, Rachel; Tartarotti, Paola; Umino, Susumu; Ziegler, Christa
Ocean Drilling Program, Leg 206, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
University of California at Santa Barbara, Department of Geological Sciences, Santa Barbara, CA, United States
Other:
University of Southampton, United Kingdom
Ocean Drilling Program, United States
University of Michigan, United States
University of Alberta, Canada
University of Leicester, United Kingdom
California Institute of Technology, United States
Universita di Genova, Italy
Université de Montpellier II, France
Florida State University, United States
Bundesanstalt für Geowissenschaften und Rohstoffe, Federal Republic of Germany
University of Utah, United States
Université d'Aix-Marseille, France
Christian-Albrechts-Universität zu Kiel, Federal Republic of Germany
Macquarie University, Australia
Universita di Milano, Italy
Shizuoka University, Japan
Boston University, United States
Volume Title: Proceedings of the Ocean Drilling Program, initial reports; an in situ section of upper oceanic crust formed by superfast seafloor spreading; covering Leg 206 of the cruises of the drilling vessel JOIDES Resolution; Balboa, Panama, to Balboa, Panama, Site 1256, 6 November 2002-4 January 2003
Volume Author(s): Wilson, Douglas S.; Teagle, Damon A. H.; Acton, Gary D.; Alt, Jeffrey C.; Banerjee, Neil R.; Barr, Samantha R.; Coggon, Rosalind; Cooper, Kari M.; Crispini, Laura; Einaudi, Florence; Jiang, Shijun; Kalberkamp, Ulrich; Kerneklian, Marcie; Laverne, Christine; Nichols, Holly J.; Sandwell, Rachel; Tartarotti, Paola; Umino, Susumu; Ziegler, Christa; Peters, Lorri L.
Source: Proceedings of the Ocean Drilling Program, initial reports; an in situ section of upper oceanic crust formed by superfast seafloor spreading; covering Leg 206 of the cruises of the drilling vessel JOIDES Resolution; Balboa, Panama, to Balboa, Panama, Site 1256, 6 November 2002-4 January 2003, Douglas S. Wilson, Damon A. H. Teagle, Gary D. Acton, Jeffrey C. Alt, Neil R. Banerjee, Samantha R. Barr, Rosalind Coggon, Kari M. Cooper, Laura Crispini, Florence Einaudi, Shijun Jiang, Ulrich Kalberkamp, Marcie Kerneklian, Christine Laverne, Holly J. Nichols, Rachel Sandwell, Paola Tartarotti, Susumu Umino, Christa Ziegler and Lorri L. Peters; Ocean Drilling Program, Leg 206, Shipboard Scientific Party, College Station, TX. Proceedings of the Ocean Drilling Program, Part A: Initial Reports, Vol.206, 117p. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 0884-5883 CODEN: IDSDA6
Note: In English. Also available on CD-ROM in PDF format and on the Web in PDF or HTML. 53 refs.CD-ROM format, ISSN 1096-2522; WWW format, ISSN 1096-2158; illus., incl. sects., 11 tables, sketch maps
Summary: Drilling a complete section of oceanic crust has been an unfulfilled ambition since the inception of scientific ocean drilling. Recovery of in situ oceanic crust is imperative to understand igneous accretion and the complex interplay between magmatic, hydrothermal, and tectonic processes, as well as a means for calibrating remote geophysical observations, particularly seismic and magnetic data. Only by drilling a complete section of upper crust formed away from fracture zones can the processes operating at normal mid-ocean ridges be understood. There is an observed relationship between the depth to axial low-velocity zones imaged at active mid-ocean ridges and spreading rate. Recent recognition of an episode of superfast spreading (200-220 mm/yr) on the East Pacific Rise ∼11-20 m.y. ago presents an opportunity to drill through the upper oceanic crust into the gabbroic rocks in minimal time. Even allowing for significant burial by lavas that have flowed off axis (∼300 m), the upper gabbros, thought to be the frozen axial melt lens, are predicted at ∼1100-1300 meters below seafloor (mbsf). During Leg 206, we completed the initial phase of a planned two-leg project to drill a complete in situ section of the upper oceanic crust that will eventually extend through the extrusive lavas and sheeted dikes and into gabbros. Drilling was conducted at Ocean Drilling Program (ODP) Site 1256 (6.736°N, 91.934°W) on ∼15-Ma oceanic lithosphere of the Cocos plate, which was formed by superfast spreading (>200 mm/yr) at the East Pacific Rise. To fully characterize the sedimentary overburden and establish depths for the casing strings, three pilot holes were cored, recovering a nearly complete section of the 250.7 m of sediment overlying basement and penetrating 88.5 m into basement with very good recovery (61.3%). The sediments can be subdivided into two main lithologies. Unit I (0-40.6 mbsf) is clay rich with a few carbonate-rich intervals, whereas Unit II (40.6-250.7 mbsf) is predominantly biogenic carbonate. More than 500 m of young Pacific extrusive lavas were cored with moderate to high rates of recovery following the installation of a reentry cone with a 16-in-diameter casing string that extended 20 m into basement in Hole 1256D. Axial sheet flows with subordinate pillow lavas, hyaloclastites, and rare dikes are capped by a more evolved massive flow >74 m thick and other sheet flows that probably ponded in small faulted depressions several kilometers off axis.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Bathymetry; Biostratigraphy; Cenozoic; Cocos Plate; Cores; Crust; East Pacific; Guatemala Basin; Igneous rocks; Leg 206; Lithostratigraphy; Miocene; Neogene; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Ocean floors; Oceanic crust; Pacific Ocean; Paleomagnetism; Pleistocene; Quaternary; Sea-floor spreading; Tertiary
Coordinates: N064200 N064200 W0915400 W0915400
Record ID: 2004021701
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