Expedition 304/305 summary

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doi: 10.2204/iodp.proc.304305.101.2006
Author(s): Blackman, Donna K.; Ildefonse, Benoit; John, Barbara E.; Ohara, Yasuhiko; Miller, D. Jay; MacLeod, Christopher J.; Einaudi, Florence; Abratis, Michael W.; Andal, Eric S.; Andreani, Muriel; Awaji, Shunsaku; Charney, Allison; Christie, David; Drouin, Marion; Frost, Bryce R.; Gee, Jeffrey S.; Godard, Marguerite M.; Grimes, Craig B.; Hayman, Nicholas W.; Hirose, Takehiro; Hirth, James Gregory; Maeda, Jinichiro; McCaig, Andrew M.; Morris, Antony; Nakagawa, Tatsunori; Searle, Roger C.; von der Handt, Anette; Delius, Heike; Abe, Natsue; Beard, James S.; Brunelli, Daniele; Delacour, Adélie G.; Escartin, Javier; Fryer, Patricia B.; Halfpenny, Angela; Hansen, Heidi-Elisabeth; Harris, Amber C.; Hasebe, Akihiro Tamura; Hellebrand, Eric; Ishimaru, Satoko; Johnson, Kevin T. M.; Karner, Garry D.; Linek, Margaret; Mason, Olivia U.; Michibayashi, Katsuyoshi; Nozaka, Toshio; Rosen, Martin; Suhr, Guenter; Tominaga, Masako; Yamasaki, Toru; Zhao, Xixi
Integrated Ocean Drilling Program, Expedition 304 and 305 Scientists, College Station, TX
Author Affiliation(s): Primary:
Scripps Institution of Oceanography, La Jolla, CA, United States
Other:
Université de Montpellier II, Canada
University of Wyoming, United States
Hydrographic and Oceanographic Department of Japan, Japan
Integrated Ocean Drilling Program, United States
Cardiff University, United Kingdom
University of Jena, Federal Republic of Germany
Kanazawa University, Japan
Institut de Physique du Globe de Paris, France
University of Tokyo, Japan
University of Connecticut, United States
Oregon State University, United States
Duke University, United States
Kyoto University, Japan
Woods Hole Oceanographic Institution, United States
Hokkaido University, Japan
University of Leeds, United Kingdom
University of Plymouth, United States
Tohoku University, Japan
University of Durham, United Kingdom
Max-Planck-Institut für Chemie, Federal Republic of Germany
University of Leicester, United Kingdom
Japan Marine Science and Technology Center, Japan
Virginia Museum of Natural History, United States
Laboratoire Pierre Süe-DRECAM, France
Eidgenössiche Technische Hochschule Zürich, Switzerland
Université Pierre et Marie Curie, France
University of Hawaii at Manoa, United States
University of Liverpool, United Kingdom
University of Bergen, Norway
University of Rhode Island, United States
Lamont-Doherty Earth Observatory, United States
Rheinisch-Westfälische Technische Hochschule Aachen, Federal Republic of Germany
Shizuoka University, Japan
Okayama University, Japan
Universität Köln, Federal Republic of Germany
University of California, Santa Cruz, United States
Université de Montpellier II, France
University of Plymouth, United Kingdom
Labortoire Pierre Süe-DRECAM, France
Eidgenössische Technische Hochschule Zürich, Switzerland
Volume Title: Oceanic core complex formation, Atlantis Massif; Expeditions 304 and 305 of the riserless drilling platform from and to Ponta Delgada, Azores (Portugal), Sites U1309-U1311, 17 November 2004-7 January 2005; and from and to Ponta Delgada, Azores (Portugal), Site U1309, 7 January-2 March 2005
Volume Author(s): Blackman, Donna K.; Ildefonse, Benoit; John, Barbara E.; Ohara, Yasuhiko; Miller, D. Jay; MacLeod, Christopher J.; Einaudi, Florence; Abratis, Michael W.; Andal, Eric S.; Andreani, Muriel; Awaji, Shunsaku; Charney, Allison; Christie, David; Drouin, Marion; Frost, Bryce R.; Gee, Jeffrey S.; Godard, Marguerite M.; Grimes, Craig B.; Hayman, Nicholas W.; Hirose, Takehiro; Hirth, James Gregory; Maeda, Jinichiro; McCaig, Andrew M.; Morris, Antony; Nakagawa, Tatsunori; Searle, Roger C.; von der Handt, Anette; Delius, Heike; Abe, Natsue; Beard, James S.; Brunelli, Daniele; Delacour, Adélie G.; Escartin, Javier; Fryer, Patricia B.; Halfpenny, Angela; Hansen, Heidi-Elisabeth; Harris, Amber C.; Hasebe, Akihiro Tamura; Hellebrand, Eric; Ishimaru, Satoko; Johnson, Kevin T. M.; Karner, Garry D.; Linek, Margaret; Mason, Olivia U.; Michibayashi, Katsuyoshi; Nozaka, Toshio; Rosner, Martin; Suhr, Guenter; Tominaga, Masako; Yamasaki, Toru; Zhao, Xixi
Source: Oceanic core complex formation, Atlantis Massif; Expeditions 304 and 305 of the riserless drilling platform from and to Ponta Delgada, Azores (Portugal), Sites U1309-U1311, 17 November 2004-7 January 2005; and from and to Ponta Delgada, Azores (Portugal), Site U1309, 7 January-2 March 2005, Donna K. Blackman, Benoit Ildefonse, Barbara E. John, Yasuhiko Ohara, D. Jay Miller, Christopher J. MacLeod, Florence Einaudi, Michael W. Abratis, Eric S. Andal, Muriel Andreani, Shunsaku Awaji, Allison Charney, David Christie, Marion Drouin, Bryce R. Frost, Jeffrey S. Gee, Marguerite M. Godard, Craig B. Grimes, Nicholas W. Hayman, Takehiro Hirose, James Gregory Hirth, Jinichiro Maeda, Andrew M. McCaig, Antony Morris, Tatsunori Nakagawa, Roger C. Searle, Anette von der Handt, Heike Delius, Natsue Abe, James S. Beard, Daniele Brunelli, Adélie G. Delacour, Javier Escartin, Patricia B. Fryer, Angela Halfpenny, Heidi-Elisabeth Hansen, Amber C. Harris, Akihiro Tamura Hasebe, Eric Hellebrand, Satoko Ishimaru, Kevin T. M. Johnson, Garry D. Karner, Margaret Linek, Olivia U. Mason, Katsuyoshi Michibayashi, Toshio Nozaka, Martin Rosner, Guenter Suhr, Masako Tominaga, Toru Yamasaki and Xixi Zhao; Integrated Ocean Drilling Program, Expeditions 304 and 305, Shipboard Scientific Parties, College Station, TX. Proceedings of the Integrated Ocean Drilling Program, Vol.304/305, 60p. Publisher: IODP Management International, Washington, DC, United States. ISSN: 1930-1014
Note: In English. 50 refs.WWW format, ISSN 1930-1014; illus., incl. sects., 1 table, geol. sketch map
Summary: Integrated Ocean Drilling Program Expeditions 304 and 305 composed a two-expedition program at Atlantis Massif, Mid-Atlantic Ridge 30°N, designed to investigate the processes that control oceanic core complex formation and the exposure of ultramafic rocks in young oceanic lithosphere. Geophysical interpretations of unaltered mantle rock occurring <1 km below the seafloor suggested we could drill through an alteration front in ultramafic rocks and obtain fresh mantle peridotite. In order to accomplish these objectives, we drilled at two sites: one in the footwall through an exposed detachment fault and one in the hanging wall. Drilling the fractured basalt in the hanging wall was thwarted by difficulties, whereas drilling in the footwall was very successful. The main hole at Site U1309 penetrated 1415.5 meters below seafloor, and recovery averaged 75%. Igneous rocks recovered from the hole are the most primitive ever cored in slow-spreading ocean lithosphere and provide an exceptional record of magmatic and tectonic accommodation to extension in this environment. The core recovered was dominantly crustal rock types: basalt (∼3%) and gabbroic (∼91%). A series of olivine-rich rocks (∼5%; dunites, wehrlites, troctolites), grouped as olivine-rich troctolites, part of which likely represent primitive cumulates, are interlayered with gabbroic rocks. A few thin mantle peridotite intervals are recognized in the upper 180 m of the section. Overall, the section is moderately altered at conditions ranging from granulite to zeolite facies. The rocks record initial alteration at low strains under granulite- and amphibolite-facies conditions and subsequent, more fully developed, lower temperature alteration (greenschist facies). Fault zone(s) comprising the detachment system must be highly localized to within tens of meters of the present-day seafloor. The existence of a fault at the top of the domal surface is supported by fragments of brecciated talc-tremolite fault schist and fractured metadiabase recovered in Hole U1309B and during the series of shallow cores drilled. Extensive amphibolite facies deformation is lacking, and high-strain ductile shear zones are rare. The absence of a thick, high-temperature ductile deformation zone in the footwall, and the apparent tectonic history (less rotation in the upper 180 m and variable rotations between several distinct, few-hundred meter sections downhole) suggested by paleomagnetic inclination measurements indicate complexity in structural evolution that differs from the simplest models of deep-rooted detachment faults, predicted to be associated with high-temperature deformation, and with constant or monotonically varying footwall rotation with depth. Another challenge is that the central dome is clearly not an uplifted dominantly upper mantle section, as had been inferred prior to drilling. The exposures of peridotite along the southern wall of Atlantis Massif, the geophysical results suggesting at least portions of the dome contain fresh olivine-rich rock, and the downhole variability at Site U1309 all likely indicate significant lateral heterogeneity over short distances across the footwall.
Year of Publication: 2005
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 05 Petrology, Igneous and Metamorphic; 18 Geophysics, Solid-Earth; Atlantic Ocean; Atlantis Massif; Basalts; Body waves; Boreholes; Bouguer anomalies; Chemical ratios; Cores; Crust; Cumulates; Density; Diabase; Drilling; Elastic waves; Expedition 304; Expedition 305; Expeditions 304/305; Facies; Faults; Gabbros; Geochemistry; Geophysical methods; Geophysical profiles; Geophysical surveys; Gravity anomalies; Heat flow; Hydrothermal alteration; IODP Site U1309; IODP Site U1310; IODP Site U1311; Igneous rocks; Integrated Ocean Drilling Program; Lithosphere; Magnetic properties; Magnetic susceptibility; Magnetostratigraphy; Marine drilling; Metamorphism; Metasomatism; Mid-Atlantic Ridge; Mid-ocean ridges; Mineral composition; North Atlantic; Oceanic crust; Oceanic lithosphere; Olivine gabbro; P-waves; Paleomagnetism; Peridotites; Petrofabrics; Petrography; Petrology; Physical properties; Plutonic rocks; Resistivity; Seismic methods; Seismic profiles; Seismic stratigraphy; Seismic waves; Seismograms; Serpentinization; Shear zones; Spatial variations; Structural analysis; Surveys; Synthetic seismograms; Thermal conductivity; Thin sections; Troctolite; Ultramafics; Veins; Velocity; Volcanic rocks; Well logs
Coordinates: N301000 N301200 W0420300 W0420800
Record ID: 2007087882
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