HR: 1340h
AN: B13A-0181    [Abstracts]
TI: Seismic Characterization of Crustal Magma Bodies at the Endeavour Segment, Juan de Fuca Ridge
AU: * Van Ark, E
EM: emilyva@mit.edu
AF: MIT-WHOI Joint Program in Marine Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Detrick, R
EM: rdetrick@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Canales, J P
EM: jpcanales@whoi.edu
AF: Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA 02543 United States
AU: Carbotte, S M
EM: carbotte@ldeo.columbia.edu
AF: Division of Marine Geology and Geophysics Lamont-Doherty Earth Observatory, 61 Route 9W - PO Box 1000, Palisades, NY 10964-8000 United States
AU: Diebold, J
EM: johnd@ldeo.columbia.edu
AF: Division of Marine Geology and Geophysics Lamont-Doherty Earth Observatory, 61 Route 9W - PO Box 1000, Palisades, NY 10964-8000 United States
AU: Kent, G
EM: gkent@ucsd.edu
AF: Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics Scripps Institute of Oceanography University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225 United States
AU: Harding, A
EM: aharding@ucsd.edu
AF: Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics Scripps Institute of Oceanography University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0225 United States
AU: Wilcock, W
EM: wilcock@ocean.washington.edu
AF: School of Oceanography University of Washington, Box 357940, Seattle, WA 98195-7940 United States
AB: Multichannel seismic reflection data collected in July 2002 at the RIDGE2000 Integrated Studies Site at the Endeavour segment, Juan de Fuca Ridge show a high-amplitude, mid-crustal reflector underlying all of the known hydrothermal vent fields at this segment. Based on the amplitude-offset behavior of this reflector, we identify it as a crustal magma body rather than a cracking front interface. The Endeavour Segment magma chamber reflector is found at two-way travel times of 0.85-1.5 s (~1.9-4.0 km) below the seafloor and extends approximately 25 km along axis although it is only 1-2 km wide on the cross-axis lines. The reflector is shallowest (at 2.5 km depth on the along-axis line) beneath the central, elevated part of the Endeavour segment and deepens toward the segment ends, with a maximum depth of 4 km. The cross axis lines show the magma chamber reflector dipping to the east with the shallowest depths under the ridge axis and greater depths under the eastern flank of the ridge. The amplitude-offset behavior of this mid-crustal axial reflector is consistent with a negative impedance contrast, indicating the presence of melt or a crystallizing mush. We have constructed tau-p transforms and partial offset stacks to examine the variation of melt-mush content of the axial magma chamber along axis. In addition, we have forward modeled the upper crustal velocity structure both on and off-axis. These velocity profiles are used to project hypocenters of well-located microseismicity in this region [Wilcock et al., 2002] onto the along-axis and cross-axis stacked seismic sections. Most axial earthquakes are concentrated in a depth range of 1.5 - 2.7 km, just above the axial magma chamber. In general, seismicity is distributed diffusely within this zone indicating thermal-related cracking above the magma chamber. However, the cross-axis line at the Salty Dawg vent field shows seismicity localized along a steeply dipping fault-like plane that terminates just above the magma chamber.
DE: 8424 Hydrothermal systems (8135)
DE: 8439 Physics and chemistry of magma bodies
DE: 7220 Oceanic crust
DE: 3025 Marine seismics (0935)
DE: 3035 Midocean ridge processes
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting