Leg 205 summary

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doi: 10.2973/odp.proc.ir.205.101.2003
Author(s): Morris, Julie D.; Villinger, Heinrich W.; Klaus, Adam; Cardace, Dawn M.; Chavagnac, Valerie M. C.; Clift, Peter D.; Haeckel, Matthias; Hisamitsu, Toshio; Kastner, Miriam; Pfender, Marion; Saffer, Demian M.; Santelli, Cara; Schramm, Burkhard; Screaton, Elizabeth J.; Solomon, Evan A.; Strasser, Michael; Thu, Moe Kyaw; Vannucchi, Paola
Ocean Drilling Program, Leg 205, Shipboard Scientific Party, College Station, TX
Author Affiliation(s): Primary:
Washington University, Department of Earth and Planetary Sciences, Saint Louis, MO, United States
Other:
Universität Bremen, Federal Republic of Germany
Ocean Drilling Program, United States
Southampton Oceanography Centre, United Kingdom
Woods Hole Oceanographic Institution, United States
Dalhousie University, Canada
Japan Marine Science and Technology Center, Japan
Scripps Institution of Oceanography, United States
University of Wyoming, United States
University of Florida, United States
Eidgenössche Technische Hochschule-Zentrum, Switzerland
Universita di Modena, Italy
Texas A&M University, United States
Eidgenössische Technische Hochschule-Zentrum, Switzerland
Universita degli Studi di Modena, Italy
Volume Title: Proceedings of the Ocean Drilling Program, initial reports; fluid flow and subduction fluxes across the Costa Rica convergent margin, implications for the seismogenic zone and subduction factory; covering Leg 205 of the cruises of the drilling vessel JOIDES Resolution; Victoria, Canada, to Balboa, Panama; sites 1253-1255; 2 September-6 November 2002
Volume Author(s): Morris, Julie D.; Villinger, Heinrich W.; Klaus, Adam; Cardace, Dawn M.; Chavagnac, Valerie M. C.; Clift, Peter D.; Haeckel, Matthias; Hisamitsu, Toshio; Kastner, Miriam; Pfender, Marion; Saffer, Demian M.; Santelli, Cara; Schramm, Burkhard; Screaton, Elizabeth J.; Solomon, Evan A.; Strasser, Michael; Thu, Moe Kyaw; Vannucchi, Paola; Nevill, Heather M.
Source: Proceedings of the Ocean Drilling Program, initial reports; fluid flow and subduction fluxes across the Costa Rica convergent margin, implications for the seismogenic zone and subduction factory; covering Leg 205 of the cruises of the drilling vessel JOIDES Resolution; Victoria, Canada, to Balboa, Panama; sites 1253-1255; 2 September-6 November 2002, Julie D. Morris, Heinrich W. Villinger, Adam Klaus, Dawn M. Cardace, Valerie M. C. Chavagnac, Peter D. Clift, Matthias Haeckel, Toshio Hisamitsu, Miriam Kastner, Marion Pfender, Demian M. Saffer, Cara Santelli, Burkhard Schramm, Elizabeth J. Screaton, Evan A. Solomon, Michael Strasser, Moe Kyaw Thu, Paola Vannucchi and Heather M. Nevill; Ocean Drilling Program, Leg 205, Shipboard Scientific Party, College Station, TX. Proceedings of the Ocean Drilling Program, Part A: Initial Reports, Vol.205, 75p. Publisher: Texas A&M University, Ocean Drilling Program, College Station, TX, United States. ISSN: 0884-5883 CODEN: IDSDA6
Note: In English. Also available on CD-ROM in PDF format and on the Web in PDF or HTML. 63 refs.CD-ROM format, ISSN 1096-2522; WWW format, ISSN 1096-2158; illus., incl. sects., strat. cols., 1 table, sketch maps
Summary: The character of the incoming plate subducting at convergent margins and the processes affecting the plate as it passes below the shallow forearc may play a major role in the nature and extent of hazardous intraplate seismicity as well as the magnitude of volcanism and the chemistry of lavas produced in the overlying volcanic arc. The fate of incoming sediments and ocean crust and of their associated volatiles as they pass through the shallow levels of a subduction zone (0-50 km depth) has profound effects on the behavior of the seismogenic zone, which produces most of the world's destructive earthquakes and tsunamis. Fluid pressure and sediment porosity influence fault localization, deformation style, and strength and may control the updip limit of the seismogenic zone. Fluids within both fault zones and sediments underthrust at the trench affect early structural development and are key agents in transport of chemical species. The mineralogy and chemistry of any subducted sediments and their dehydration reactions, governed by the thermal structure of the plate during subduction, may control the physical properties of the deeper subduction interface and, hence, the updip and downdip limits of the seismogenic zone wherein interplate earthquakes are generated. The mineralogy, composition, and volatile content of the slab, transformed during its progress through the shallow subduction zone, will govern the flux of fluids or melts from slab to mantle wedge, which is an important control on the extent of mantle melting and formation of arc lavas. Costa Rica is an important area for studies of the seismogenic zone and subduction factory for several reasons. As one of the few modern arcs subducting a carbonate-rich sediment section, Central America permits study of CO2 recycling through a subduction zone. Changes along strike in seismicity, plate coupling, and volume and composition of the arc lavas (between Nicaragua and Costa Rica) appear to correlate with changes in sediment dynamics. The balance between sediment accretion, underplating, erosion, and subduction may ultimately result from changing bathymetry, thermal structure, or hydrological behavior along the margin. Science objectives for Leg 205 had two primary foci, both related to seismogenic zone and subduction factory questions. The first was to determine the igneous and alteration history of the uppermost part of the downgoing plate at reference Site 1253, along with the inferred distribution of fracture permeability in the core and borehole. The second was to characterize and monitor two of the three hydrological systems inferred from Leg 170 results: in basement at Site 1253 and along the decollement (or upper fault zone) at Sites 1254 and 1255. These goals were accomplished by (1) targeted coring of selected intervals, (2) downhole temperature and pressure measurements, (3) logging at Site 1253, and (4) installation of long-term observatories (CORK-IIs) to monitor temperature and pressure and to sample fluids and gases in each of the hydrologic systems. In the decollement zone, instruments were also deployed to attempt to measure fluid flow rates. Temporal variation of fluid composition in the sealed-off intervals will be obtained using osmotic fluid samplers. The samplers and temperature loggers will be recovered for analysis 1 to 2 years after installation, pressure data will be downloaded, and new samplers and temperature probes will be installed.....
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; 18 Geophysics, Solid-Earth; Bathymetry; CORK-II; Central America; Cores; Costa Rica; East Pacific; Geophysical methods; Geophysical profiles; Geophysical surveys; Heat flow; Leg 205; Lithostratigraphy; Middle America Trench; North Pacific; Northeast Pacific; ODP Site 1253; ODP Site 1254; ODP Site 1255; Observatories; Ocean Drilling Program; Ocean floors; Pacific Ocean; Plate convergence; Plate tectonics; Seismic methods; Seismic profiles; Seismicity; Subduction; Subduction zones; Surveys; Tectonics
Coordinates: N093800 N094000 W0861000 W0861200
Record ID: 2004014635
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