HR: 1330h
AN: T12D-0490    [PDF]
TI: Deep Crustal Structure of Fast-Spreading Crust Near Hess Deep
AU: * Brothers, D S
EM: brotherd@colorado.edu
AF: University of Colorado-Boulder, Department of Geological Sciences, Boulder, CO 80310 United States
AU: Christeson, G L
EM: gail@ig.utexas.edu
AF: Univ TX Institute For Geophysics, 4412 Spicewood Springs Rd, Bldg 600, Austin, TX 78759 United States
AU: McIntosh, K D
EM: kirk@ig.utexas.edu
AF: Univ TX Institute For Geophysics, 4412 Spicewood Springs Rd, Bldg 600, Austin, TX 78759 United States
AB: We present the results of a wide-angle seismic survey conducted near Hess Deep in the equatorial East Pacific. Hess Deep is a rift velley in ~1 Ma crust formed at the fast-spreading East Pacific Rise (EPR). Rifting is characterized by north/south extension and the westward propagating Cocos-Nazca spreading center. Geologic investigations of the northern wall of the valley using deep-sea submersibles have mapped the lithologic boundaries exposed here. The experiment took place on top the northern wall of the rift valley and consisted of three scarp parallel lines of ocean bottom seismograph (OBS) receivers. The instruments were separated by 7.5 km on two of the lines and 3.5 km on the third. We used two-dimensional ray-tracing to constrain velocity structure in the region and then made comparisons with the geologic structure observed by the submersible teams. For each profile we present a four layer crustal velocity model consisting of layer 2A (2.85-3.15 km/s), 2B (5.1-6.7 km/s), layer 3 (6.35-7.35 km/s) and mantle (8.0 km/s). It has been suggested that the seismic layer 2/3 boundary may correspond to the lithologic contact between dikes and gabbros. However, the velocity structure closest to the fault scarp indicates seismic boundary 2/3 is nearly 1 km below the observed dike/gabbro layer. Overall, the seismic boundaries of the two lines further from the scarp are very similar, but the line closest the scarp presents a slower than expected velocity at the top of layer 3 (6.25-6.35 km/s). The average crustal thickness in the region is ~5.9 km.
DE: 3025 Marine seismics (0935)
DE: 3035 Midocean ridge processes
SC: Tectonophysics [T]
MN: 2003 Fall Meeting