Integrated Ocean Drilling Program Expedition 312 preliminary report (including Expedition 309 accomplishments); superfast spreading rate crust 3; a complete in situ section of upper oceanic crust formed at a superfast spreading rate; 28 October-28 December 2005

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doi: 10.2204/iodp.pr.312.2006
Author(s): Teagle, Damon A. H.; Umino, Susumu; Banerjee, Neil R.; Einaudi, Florence; Alt, Jeffrey C.; Miyashita, Sumio; Belghoul, Akram; Cordier, Carole; Crispini, Laura; Galli, Laura; Gao, Yongjun; Geldmacher, Jörg; Gilbert, Lisa A.; Herrero-Bervera, Emilio; Holter, Sara Ann; Laverne, Christine; Vasquez, Haroldo L. Lledo; Rodriguez Durand, Sedelia; Sakuyama, Tetsuya; Sano, Takashi; Smith-Duque, Christopher E.; Tominaga, Masako; Tartarotti, Paola; Veloso Espinosa, Eugenio A.; Wilson, Douglas S.; Reichow, Marc K.; Anma, Ryo; Carlut, Julie; Christie, David M.; Coggon, Rosalind; Galli, Laura; Hayman, Nicholas W.; Hirano, Nobuo; Ingle, Stephanie; Koepke, Juergen; Laverne, Christine; Maclennan, John; Morgan, Sally; Neo, Natsuki; Park, Sung-Hyun; Scheibner, Birgit; Swift, Stephen A.; Tikku, Anahita A.; Yamasaki, Toru; Yamazaki, Shusaku
Integrated Ocean Drilling Program, Expedition 309 Scientists, College Station, TX
Author Affiliation(s): Primary:
University of Southampton, National Oceanography Centre, Southampton, United Kingdom
Other:
Shizuoka University, Japan
Integrated Ocean Drilling Program, United States
ISTEEM, France
University of Michigan, United States
Niigata University, Japan
Universite de Bretagne Occidentale, France
Universita di Genova, Italy
Universita di Milano, Italy
University of Houston, United States
Leibniz Institute for Marine Sciences Kiel, Federal Republic of Germany
Williams College and Mystic Seaport, United States
University of Hawaii at Manoa, United States
University of St. Thomas, United States
Université Paul Cézanne Aix-Marseille III, France
Binghamton University, United States
Florida International University, United States
University of Tokyo, Japan
Fuji Tokoha University, Japan
University of Tsukuba, Japan
University of California-Santa Barbara, United States
University of Leicester, United Kingdom
École Normale Supérieure, France
Oregon State University, United States
Duke University, United States
Tohoku University, Japan
Universität Hannover, Federal Republic of Germany
University of Edinburgh, United Kingdom
University of Leeds, United Kingdom
Seoul National University, South Korea
Universität Karlsruhe, Federal Republic of Germany
Woods Hole Oceanographic Institution, United States
Rensselaer Polytechnic Institute, United States
Hokkaido University, Japan
Source: Preliminary Report (Integrated Ocean Drilling Program), Vol.312, 11p. Publisher: IODP Management International, College Station, TX, United States. ISSN: 1932-9423
Note: In English. 85 refs.
Summary: The Superfast Spreading Rate Crust mission is a multicruise program to drill, for the first time, a complete section of the upper oceanic crust from extrusive lavas, through the dikes, and into the underlying gabbros. Hole 1256D was initiated during Ocean Drilling Program Leg 206 in the eastern equatorial Pacific and is drilled into 15 Ma crust that formed at the East Pacific Rise during a period of superfast spreading (>200 mm/y). This site is chosen to exploit the inverse relationship between spreading rate and the depth to axial low-velocity zones, thought to be magma chambers now frozen as gabbros, observed from seismic experiments. During Integrated Ocean Drilling Program (IODP) Expedition 309, Hole 1256D was deepened to a total depth of 1255 meters below seafloor (mbsf) (1005 m subbasement), having penetrated >800 m of extrusive normal mid-ocean-ridge basalt, and entered the sheeted dike complex. Expedition 312 returned to Hole 1256D and deepened it to 1507.1 mbsf. The hole now extends through the 345 m sheeted dike complex and 100.5 m into the upper portions of the plutonic complex. The uppermost crust at Site 1256 comprises a >74 m thick ponded lava overlying massive, sheet, and minor pillow flows, some of which exhibit inflation structures requiring eruption onto a subhorizontal surface. This suggests a total thickness of off-axis lavas of 284 m. Sheet and massive lava flows make up the remaining extrusive section (534-1004 mbsf) above subvertical cataclastic zones, intrusive contacts, and mineralized breccias denoting a lithologic transition zone. Below 1061 mbsf, massive basalts, some with doleritic textures, dominate the sheeted dikes, which exhibit increased thermal conductivity and P-wave velocity. Numerous subvertical dikes, commonly with brecciated and mineralized chilled margins, crosscut the sheeted dikes. The upper dikes (<1255 mbsf) contain greenschist facies minerals, actinolite becomes abundant below ∼1300 mbsf, and hornblende and secondary plagioclase are present below ∼1350 mbsf, reflecting a steep thermal gradient in the dikes. Superimposed on this is recrystallization of the lowermost 50 m of dikes to granoblastic textures as the result of intrusion of underlying gabbros. An upper gabbroic body intrudes the sheeted dikes at 1406.6 mbsf and is separated from a lower gabbroic body at 1483-1507.1 mbsf by an intervening metamorphosed dike screen. Gabbroic rocks are highly altered, fine to coarse grained (mostly medium grained), range from gabbro to oxide gabbro and gabbronorite, and include differentiated rocks (trondjhemite and quartz-rich oxide diorite). The base of the section contains a gabbronorite of uncertain origin (intrusive gabbronorite or metamorphosed dike) and is cut by a late basalt dike. Physical properties change downward across the dike/gabbro contact (increased porosity and decreased velocity and density).
Year of Publication: 2006
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; Alteration; Basalts; Basement; Boreholes; Chemical ratios; Chemostratigraphy; Cocos Plate; Cores; Crust; Deformation; Depth; Dikes; Drilling; East Pacific; Equatorial Pacific; Expeditions 309/312; Gabbros; Geochemistry; Geophysical methods; Geophysical profiles; Geophysical surveys; Guatemala Basin; Igneous rocks; Integrated Ocean Drilling Program; Intrusions; Lava; Lithostratigraphy; Low-velocity zones; Magnetic anomalies; Major elements; Marine drilling; Mid-ocean ridge basalts; Mineral composition; North Pacific; Northeast Pacific; ODP Site 1256; Ocean Drilling Program; Oceanic crust; Pacific Ocean; Paleomagnetism; Phenocrysts; Physical properties; Plate tectonics; Plutonic rocks; Rates; Sea-floor spreading; Secondary minerals; Seismic methods; Seismic profiles; Sheeted dikes; Surveys; Trace elements; Upper crust; Velocity structure; Volcanic rocks; Well logs
Coordinates: N064400 N064400 W0915600 W0915600
Record ID: 2008016940
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