Leg 206 synthesis; initiation of drilling an intact section of upper oceanic crust formed at the superfast spreading rate at Site 1256 in the eastern Equatorial Pacific

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doi: 10.2973/odp.proc.sr.206.001.2007
Author(s): Teagle, Damon A. H.; Wilson, Douglas S.
Ocean Drilling Program, Leg 206, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
University of Southampton, National Oceanography Centre, Southampton, United Kingdom
Other:
University of California, Santa Barbara, United States
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
Universitë de 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
University of California, Santa Barabara, United States
Volume Title: Proceedings of the Ocean Drilling Program; volume 206; scientific results; an in situ section of the 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): Teagle, Damon A. H.; Wilson, Douglas S.; 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 J.; Laverne, Christine; Nichols, Holly J.; Sandwell, Rachel; Tartarotti, Paola; Umino, Susumu; Ziegler, Christa
Source: Proceedings of the Ocean Drilling Program; volume 206; scientific results; an in situ section of the 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, Damon A. H. Teagle, Douglas S. Wilson, 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 J. Kerneklian, Christine Laverne, Holly J. Nichols, Rachel Sandwell, Paola Tartarotti, Susumu Umino and Christa Ziegler; Ocean Drilling Program, Leg 206, Shipboard Scientific Party, College Station, TX. Proceedings of the Ocean Drilling Program, Scientific Results (CD ROM), Vol.206, 15p. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 1096-2514
Note: In English. 27 refs.CD-ROM format, ISSN 1096-2514; WWW format, 1096-7451; illus., incl. geol. sketch map
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 understanding igneous accretion and the complex interplay between magmatic, hydrothermal, and tectonic processes, as well as providing a means for calibrating remote geophysical observations, particularly seismic and magnetic data. Ocean Drilling Program (ODP) Leg 206 was the initial phase of the Superfast Spreading Rate Crust campaign to ODP Site 1256, a multicruise program to exploit the observed relationship between the depth to axial low-velocity zones imaged at active mid-ocean ridges and spreading rate. Because of the known difficulties of drilling young ocean basement, targeting a region where gabbros should occur at their shallowest optimizes the chances of reaching gabbro in intact ocean crust by reducing the distance to be drilled and the time required on site. Following the recent recognition of an episode of superfast spreading (200-220 mm/yr) on the East Pacific Rise ∼11-20 m.y. ago, Site 1256 (6.736°N, 91.934°W) on ∼15-Ma oceanic lithosphere of the Cocos plate was identified as the optimal site for a new deep drill hole into ocean crust. Even allowing for significant burial by lavas that flowed off axis (∼300 m), the upper gabbros, thought to be the frozen axial melt lens, are predicted at ∼1275-1550 meters below seafloor (mbsf). 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. Following installation of a reentry cone with a 16-in-diameter casing string that extended 20 m into basement in Hole 1256D, >500 m of young Pacific extrusive lavas was cored with moderate to high rates of recovery. These upper lavas comprise sheet flows with subordinate pillow lavas, hyaloclastites, and rare dikes, capped by an evolved, massive flow >74 m thick and other sheet flows that probably ponded in small faulted depressions several kilometers off axis. The lavas have normal mid-ocean-ridge basalt chemistries, with evolved compositions more common upsection, and heterogeneous incompatible element ratios. Hole 1256D was exited cleanly, leaving the hole clear of debris, open to its full depth, and primed for the future deepening into the sheeted dikes and gabbros that took place early in the next phase of scientific ocean drilling during Integrated Ocean Drilling Program Expeditions 309 and 312. This Scientific Results volume comprises a collection of papers, mostly data reports, of the initial postcruise research undertaken by the ODP Leg 206 science party. This synthesis also briefly describes research published to date in the external scientific literature. With follow- up cruises to deepen Hole 1256D occurring soon after Leg 206, we anticipate that numerous future manuscripts and data that investigate the complete upper crustal section at Site 1256 will soon be available in the wider scientific literature.
Year of Publication: 2007
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Basalts; Basement; Biostratigraphy; Boreholes; Cenozoic; Cores; Crust; East Pacific; Equatorial Pacific; Geochemistry; Guatemala Basin; Hydrothermal alteration; Igneous rocks; Lava; Leg 206; Lithostratigraphy; Metasomatism; Mid-ocean ridge basalts; Mineral composition; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Sea-floor spreading; Sedimentary rocks; Upper crust; Volcanic rocks
Coordinates: N064400 N064400 W0915600 W0915600
Record ID: 2007124228
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