Teagle, Damon A. H. et al. (2005): Integrated Ocean Drilling Program Expedition 309 preliminary report; superfast spreading rate crust 2; a complete in situ section of upper oceanic crust formed at a superfast spreading rate; 8 July-28 August 2005

IODP 309
IODP 309 U1256
IODP 312 U1256



Teagle, Damon A. H.
University of Southampton, National Oceanography Centre, Southampton, United Kingdom

Umino, Susumu
Shizuoka University, Japan

Banerjee, Neil R.
Integrated Ocean Drilling Program, United States

Einaudi, Florence
ISTEEM, France

Vasquez, Haroldo L. Lledo
Binghamton University, United Kingdom

Sakuyama, Tetsuya
University of Tokyo, Japan

Gao, Yongjun
University of Houston, United States

Wilson, Douglas S.
University of California Santa Barbara, United States

Herrero-Bervera, Emilio
University of Hawaii at Manoa, United States

Espinosa, Eugenio A. Veloso
University of Tsukuba, Japan

Cordier, Carole
Universite de Bretagne Occidentale, France

Geldmacher, Joerg
Leibniz Institute for Marine Sciences Kiel, Federal Republic of Germany

Durand, Sedelia Rodriguez
Florida International University, United States

Sano, Takashi
Fuji Tokoha University, Japan

Laverne, Christine
Universite Paul Cezanne Aix-Marseille III, France

Smith-Duque, Christopher E.
Williams College, United States

Gilbert, Lisa A.
Universita di Genova, Italy

Tominaga, Masako
Universita di Milano, Italy

Crispini, Laura
University of St. Thomas, United States

Galli, Laura

Tartarotti, Paola

Holter, Sara Ann

Belghoul, Akram

Integrated Ocean Drilling Program Expedition 309 preliminary report; superfast spreading rate crust 2; a complete in situ section of upper oceanic crust formed at a superfast spreading rate; 8 July-28 August 2005
Preliminary Report (Integrated Ocean Drilling Program)
IODP Management International, College Station, TX, United States
128 pp.
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 successfully deepened to a total depth of 1255 meters below seafloor (mbsf) (1005 m subbasement), having penetrated through >800 m of extrusive normal mid-ocean-ridge basalt, and entered a region dominated by intrusive rocks with numerous subvertical chilled dike margins. 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 spectacular mineralized breccias denoting a lithologic transition zone. The extrusive lavas are less hydrothermally altered than other basement sites (e.g., Sites 417 and 418 and Holes 504B and 896A), and there is no systematic change with depth from oxidizing to reducing seawater alteration. Instead, oxidizing alteration occurs irregularly with depth, most commonly associated with steeply dipping vein networks. Below 1061 mbsf, massive basalts, some with doleritic textures, dominate the sheeted intrusives. Numerous subvertical dikes, commonly with brecciated and mineralized chilled margins, crosscut the sheeted intrusives. These rocks are altered under greenschist facies hydrothermal conditions and have significantly higher thermal conductivity and P-wave velocity. During Expedition 309 Hole 1256D was exited cleanly, and the hole is in excellent condition and ready for deepening. At 1255 mbsf, Hole 1256D is tantalizingly close to the minimum estimated depth for the frozen axial magma chamber predicted to be at 1275-1525 mbsf. IODP Expedition 312 will return to this site in late 2005, and, despite the grueling 15 m/day pace of advance and assuming further benign drilling conditions, is set to deepen Hole 1256D by a further 500 m. The total depth would then be well beyond where geophysical interpretations predict gabbros to occur.
Coverage:Geographic coordinates:
West:-91.5600East: -91.5600

Solid-earth geophysics; alteration; basalts; basement; body waves; boreholes; breccia; chemical ratios; Cocos Plate; cores; crust; depth; dikes; drilling; East Pacific; elastic waves; Equatorial Pacific; Expedition 309; gabbros; geochemistry; Guatemala Basin; igneous rocks; Integrated Ocean Drilling Program; intrusions; lava; lithostratigraphy; low-velocity zones; magnetic anomalies; magnetic intensity; marine drilling; mid-ocean ridge basalts; mineral composition; North Pacific; Northeast Pacific; Ocean Drilling Program; oceanic crust; ODP Site 1256; P-waves; Pacific Ocean; paleomagnetism; physical properties; plate tectonics; plutonic rocks; rates; sea-floor spreading; secondary minerals; seismic waves; sheeted dikes; velocity structure; volcanic rocks; well logs;