Leg 195 synthesis; Site 1201; a geological and geophysical section in the West Philippine Basin from the 660-km discontinuity to the mudline

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doi: 10.2973/odp.proc.sr.195.113.2006
Author(s): Salisbury, Matthew H.; Shinohara, Masanao; Suetsugu, Daisuke; Arisaka, Michio; Diekmann, Bernhard; Januszczak, Nicole; Savov, Ivan P.
Ocean Drilling Program, Leg 195, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
Geological Survey of Canada, Bedford Institute of Oceanography, Dartmouth, NS, Canada
Other:
Geological Survey of Canada, Canada
Ocean Drilling Program, United States
Japan Agency for Marine-Earth Science and Technology, Japan
University of Leicester, United Kingdom
Universita di Napoli "Federico II", Italy
University of Southampton, United Kingdom
Alfred Wegener Institute for Polar and Marine Research, Federal Republic of Germany
Rosenstiel School of Marine and Atmospheric Science, United States
University of Hawaii at Manoa, United States
ISTEEM, Laboratoire de Tectonophysique, France
University of Texas at Dallas, United States
University of Wisconsin at Madison, United States
University of Toronto at Scarborough, Canada
U. S. Geological Survey, United States
University of Aarhus, Denmark
Western Washington University, United States
University of South Florida, United States
China University of Geosciences, China
National Taiwan University, Taiwan
University of Tokyo, Japan
Japan Marine Science and Technology Center, Japan
Volume Title: Proceedings of the Ocean Drilling Program; scientific results; seafloor observatories and the Kuroshio Current; covering Leg 195 of the cruises of the drilling vessel JOIDES Resolution; Apra Harbor, Guam, to Keelung, Taiwan; Sites 1200-1202; 2 March-2 May 2001
Volume Author(s): Shinohara, Masanao, editor; Salisbury, Matthew H.; Richter, Carl; Araki, Eiichiro; Barr, Samantha R.; D'Antonio, Massimo; Dean, Simon M.; Diekmann, Bernhard; Edwards, K. Michelle; Fryer, Patricia B.; Gaillot, Philippe J.; Hammon, William S., III; Hart, David; Januszczak, Nicole; Komor, Stephen C.; Kristensen, Mette B.; Lockwood, John P.; Mottl, Michael J.; Moyer, Craig L.; Nakahigashi, Kazuo; Savov, Ivan P.; Su Xin; Wei, Kuo-Yen; Yamada, Tomoaki
Source: Proceedings of the Ocean Drilling Program; scientific results; seafloor observatories and the Kuroshio Current; covering Leg 195 of the cruises of the drilling vessel JOIDES Resolution; Apra Harbor, Guam, to Keelung, Taiwan; Sites 1200-1202; 2 March-2 May 2001, Masanao Shinohara, Matthew H. Salisbury, Carl Richter, Eiichiro Araki, Samantha R. Barr, Massimo D'Antonio, Simon M. Dean, Bernhard Diekmann, K. Michelle Edwards, Patricia B. Fryer, Philippe J. Gaillot, William S. Hammon, III, David Hart, Nicole Januszczak, Stephen C. Komor, Mette B. Kristensen, John P. Lockwood, Michael J. Mottl, Craig L. Moyer, Kazuo Nakahigashi, Ivan P. Savov, Su Xin, Kuo-Yen Wei and Tomoaki Yamada; Ocean Drilling Program, Leg 195, Shipboard Scientific Party, College Station, TX. Proceedings of the Ocean Drilling Program, Scientific Results (CD ROM), Vol.195, 27p. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 1096-2514
Note: In English. Also available on CD-ROM in PDF format and on the Web in PDF or HTML. 43 refs.CD-ROM, ISSN 1096-2514; WWW, ISSN 1096-7451; illus., incl. sects., strat. cols., geol. sketch maps
Summary: The installation of a borehole seismic observatory 500 m below the seafloor at Site 1201 in the West Philippine Basin has created a unique listening post for long- and short-term seismic studies of the Earth's asthenosphere and lithosphere, as well as the crust and upper mantle near one of the most active subduction complexes in the world. Broadband waveforms recorded by ocean bottom seismometers across the Philippine Sea and the borehole seismometer at Site 1201 show that the 410- and 660-km discontinuities are located at depths of 377 and 669 km, respectively, below the site, whereas controlled-source experiments over the site show the crust to be abnormally thin (3.8 km). Layer 3, which is only 2.3 km thick, is strongly anisotropic, with VP = 6.7 km/s in the east-west direction, but only 6.3 km/s in the north-south (paleospreading) direction, probably due to faults and fissures. Coring at Site 1201 shows the upper crust to be transitional in composition between arc tholeiites and mid-ocean-ridge basalt (MORB), which is consistent with the formation of the West Philippine Basin by backarc spreading between two opposed subduction zones beginning in the Eocene. After the site drifted northwest away from the spreading axis and volcanism ceased, 0.5 km of sediments was deposited in three stages: (1) quiescent marine sedimentation in deep water into the late Eocene; (2) pelagic sedimentation mixed with, and finally overwhelmed by, volcaniclastic turbidites from the Palau-Kyushu Ridge from the late Eocene through the early Oligocene; and (3) waning turbidite deposition, followed by barren, deep-sea pelagic sedimentation below the carbonate compensation depth (CCD) from the early Oligocene to the early Pliocene, when sedimentation ceased altogether. Extensive low-temperature (100°-150°C) zeolite facies hydrothermal alteration occurred in many of the basalts under oxidizing open-circulation conditions, which became more restricted as sedimentation proceeded. In the overlying sediments, the deeper levels of the turbidites have undergone profound low-temperature (<100°C) diagenesis, causing the vitric shards in the turbidites to be completely replaced by smectite, mixed-layer clays, and zeolites and the interstitial seawater to be replaced by pore water that is extremely enriched in Ca and depleted in K and Mg, consistent with alteration of basaltic glass to zeolites and clays. High geochemical gradients in the pore waters above 300 meters below seafloor (mbsf) suggest that alteration is continuing at present in the upper turbidites but that below 300 mbsf the pore water has reached equilibrium with the products of alteration.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 18 Geophysics, Solid-Earth; 20 Geophysics, Applied; 670-km discontinuity; Boreholes; Crust; Geophysical methods; Geophysical profiles; Geophysical surveys; Leg 195; Lithosphere; Mantle; North Pacific; Northwest Pacific; ODP Site 1201; Ocean Drilling Program; Ocean floors; Oceanic crust; Oceanic lithosphere; Pacific Ocean; Philippine Sea; Sedimentary cover; Seismic methods; Seismic profiles; Surveys; Waveforms; West Pacific; West Philippine Basin
Coordinates: N191700 N191800 E1350600 E1350500
Record ID: 2006066602
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