HR: 1330h
AN: B12A-0752    [PDF]
TI: Seismic Structure of the Endeavour Segment, Juan de Fuca Ridge: Correlations of Crustal Magma Chamber Properties With Seismicity, Faulting, and Hydrothermal Activity
AU: * Van Ark, E M
EM: emilyva@mit.edu
AF: MIT-WHOI Joint Program in Oceanography, 77 Massachusetts Ave, 54-517A, Cambridge, MA 02139
AU: Detrick, R S
EM: rdetrick@whoi.edu
AF: Dept of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543
AU: Canales, J P
EM: jpcanales@whoi.edu
AF: Dept of Geology and Geophysics, Woods Hole Oceanographic Institution, 360 Woods Hole Rd, Woods Hole, MA 02543
AU: Carbotte, S M
EM: carbotte@ldeo.columbia.edu
AF: Marine Geology and Geophysics Division, Lamont-Doherty Earth Observatory, PO Box 1000, Palisades, NY 10964
AU: Diebold, J B
EM: johnd@ldeo.columbia.edu
AF: Marine Geology and Geophysics Division, Lamont-Doherty Earth Observatory, PO Box 1000, Palisades, NY 10964
AU: Harding, A
EM: aharding@ucsd.edu
AF: Scripps Instituion of Oceanography, Univ. of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093
AU: Kent, G
EM: gkent@ucsd.edu
AF: Scripps Instituion of Oceanography, Univ. of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093
AU: Nedimovic, M R
EM: mladen@ldeo.columbia.edu
AF: Marine Geology and Geophysics Division, Lamont-Doherty Earth Observatory, PO Box 1000, Palisades, NY 10964
AU: Wilcock, W S
EM: wilcock@ocean.washington.edu
AF: School of Oceanography, University of Washington, Box 357940, Seattle, WA 98195
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. This reflector, which has been identified with a crustal magma body [Detrick et al., 2002], is found at a two-way travel time 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 (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 mid-crustal reflector dipping from 9 to 50? 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 partial offset stacks at 2-3 km offset to examine the variation of melt-mush content of the axial magma chamber along axis. We see a decrease in P-wave amplitudes with increasing offset for the mid-crustal reflector beneath the Mothra and Main Endeavour vent fields and between the Salty Dawg and Sasquatch vent fields, indicating the presence of a melt-rich body. Beneath the High Rise, Salty Dawg, and Sasquatch vent fields P-wave amplitudes vary little with offset suggesting the presence of a more mush-rich magma chamber. Hypocenters of well-located microseismicity in this region [Wilcock et al., 2002] have been projected onto the along-axis and cross-axis seismic lines, revealing that 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, although 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. A faint reflector at ~1.5 km below the seafloor (~700 m below the layer 2a reflector) is present near the top of this axial zone of seismicity and may represent a cracking-related boundary in the porosity structure of the shallow crust.
DE: 3025 Marine seismics (0935)
DE: 3035 Midocean ridge processes
DE: 7220 Oceanic crust
DE: 8135 Hydrothermal systems (8424)
DE: 9355 Pacific Ocean
SC: Biogeosciences [B]
MN: 2003 Fall Meeting